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Zdenek Kaplan, PhD
Selected publications with their abstracts
 
Chytrý M., Danihelka J., Kaplan Z. & Pyšek P. (eds) (2017): Flora and vegetation of the Czech Republic. – 466 p., Springer, Cham. [ISBN: 978-3-319-63180-6] [DOI: 10.1007/978-3-319-63181-3]
This book summarizes basic information on the diversity of vascular plants, bryophytes, lichens and plant communities in the Czech Republic. It explains the patterns in botanical diversity in this country by linking them to environmental factors, biogeographical history and human impact. Basic taxonomic accounts of the flora are completed with an analysis of relict, endemic, rare and other biogeographically important species. The history of vegetation since the late Pleistocene is characterized based on a new synthesis of palaeoecological data and types of current vegetation are described following a recently developed system of national vegetation classification. Special attention is paid to the altitudinal zonation of vegetation, areas with high diversity of different vegetation types, species richness of plant communities, dynamics of current changes in vegetation and underlying causes. Alien flora is characterized separately with emphasis on the dynamics of the spread of introduced species, patterns in the invasibility of habitats and landscapes, and impact and management of alien plants. Individual species of invasive alien plants are characterized in detail. Finally, various aspects of conservation of botanical diversity are assessed, including its legal basis, protected plant species, Red List and Red Data Book, national system of protected areas, Natura 2000 network in the Czech Republic, mapping of habitats for conservation purposes, management of threatened plant species and their habitats and ecological restoration. This book also contains a basic description of the physical geography of this country, emphasizing the factors that shape the patterns in botanical diversity, and a detailed overview of the history of botanical research since the Renaissance up to the present. The flora and vegetation in this country is illustrated by numerous maps, graphs and photographs of plant species and communities.
 
Kaplan Z. (2017): Flora and phytogeography of the Czech Republic. – In: Chytrý M., Danihelka J., Kaplan Z. & Pyšek P. (eds), Flora and vegetation of the Czech Republic, p. 89–163, Springer, Cham. [DOI: 10.1007/978-3-319-63181-3_3]
An overview of the diversity of vascular plants in the Czech Republic is presented. This country is situated at the intersection of several assumed important European migration routes. Consequently, the flora is composed of almost all the floristic elements that occur in Central Europe, of which the Central European geoelement is dominant. The occurrence of various sorts of relicts is discussed in the context of the changes in vegetation caused by Pleistocene climatic fluctuations. An account of Czech endemics includes 82 species and subspecies, which is 2.2% of the total vascular plant diversity in this country. Patterns in the distribution and occurrence of endemics in different habitat types are described. Groups of species with similar ecogeographical features within the Czech Republic are distinguished as regional types of distribution. Phytogeographical division of the country is described and the phytogeographical units distinguished are shown on a map.
 
Kaplan Z., Danihelka J., Šumberová K., Chrtek J. Jr., Rotreklová O., Ekrt L., Štěpánková J., Taraška V., Trávníček B., Prančl J., Ducháček M., Hroneš M., Kobrlová L., Horák D. & Wild J. (2017): Distributions of vascular plants in the Czech Republic. Part 5. – Preslia 89: 333–439.
The fifth part of the series on the distributions of vascular plants in the Czech Republic includes grid maps of 106 taxa of the genera Arnica, Carduus, Cicuta, Coleanthus, Comarum, Dactylorhiza, Digitaria, Gagea, Gypsophila, Hieracium, Hydrocotyle, Leersia, Myosurus, Oenanthe, Oreopteris, Paris, Phalaris, Phegopteris, Pilosella, Polystichum, Portulaca, Pulicaria, Salicornia, Saxifraga, Suaeda, Thalictrum, Thelypteris, Tripolium, Utricularia, Veronica and Xeranthemum. These maps were produced by taxonomic experts based on herbarium specimens, literature and field records. Almost two-thirds of the mapped taxa are on the national Red List. These include endangered plants of rather dry habitats such as Gypsophila paniculata, Thalictrum foetidum, Veronica austriaca and Xeranthemum annuum as well as species of various sorts of wetlands such as Cicuta virosa and species of the genera Dactylorhiza and Utricularia, or fens and intermittently wet meadows including Oenanthe fistulosa, Thalictrum flavum and Th. simplex subsp. galioides. Particularly endangered are ecological specialists; for example, many species of saline habitats such as Salicornia perennans and Suaeda prostrata, both confined to saline habitats, are now extirpated from this country. In contrast, Saxifraga tridactylites, previously a rare species found mainly on base-rich rock outcrops, has become more abundant by spreading along railways during the last two decades. Maps based solely or mainly on herbarium records revised by experts are provided for taxonomically critical groups, particularly those of the genus Pilosella. Alien species mapped in this paper include both archaeophytes and neophytes, with various modes of introduction. For example, Carduus tenuiflorus has been introduced with wool, Digitaria ciliaris with cotton, Gypsophila perfoliata with iron ore from Ukraine, while the ornamentals G. elegans and G. scorzonerifolia escaped from cultivation. The halophytic Suaeda salsa is recorded as a new alien species for this country’s flora; it has recently colonized motorway verges of which the salinity of the soil was increased by the application of de-icing salts. Two archaeophyte species, Digitaria ischaemum and Portulaca oleracea, are now classified as invasive. Spatial distributions and often also temporal dynamics of individual taxa are shown in maps and documented by records included in the Pladias database and available in electronic appendices. The maps are accompanied by comments, which include additional information on the distribution, habitats, taxonomy and biology of the taxa.
 
Aykurt C., Fehrer J., Sari D., Kaplan Z., Deniz I. G., Aydemir E. & Imir N. (2017): Hybridization between the linear-leaved Potamogeton species in Turkey. – Aquatic Bot. 141: 22–28.
Hybridization is an important source of generating diversity in Potamogeton. However, the recorded frequency and distribution of hybrids in the world is highly uneven, and so is our knowledge of this diversity. So far, no hybrid between linear-leaved species has been recorded in Turkey. Morphologically intermediate and taxonomically unclear forms collected during an extensive field survey in wetlands throughout Turkey were subjected to detailed morphological and molecular analyses. Direct sequencing and cloning of the ITS region revealed two hybrids previously unknown in Turkey: P. obtusifolius × P. berchtoldii and P. trichoides × P. berchtoldii. Sequences of the chloroplast trnL-trnF intergenic spacer region confirmed P. obtusifolius and P. trichoides as maternal parents of these hybrids. One of the maternal species, P. obtusifolius, is not known to currently occur in Turkey. Brief morphological descriptions of the new hybrids are provided, as well as a comparison of diagnostic characters with those of all parental and similar linear-leaved species. These results demonstrate that hybridization studies and appropriate approaches bring important information about both past and present biodiversity.
 
Kaplan Z., Danihelka J., Koutecký P., Šumberová K., Ekrt L., Grulich V., Řepka R., Hroudová Z., Štěpánková J., Dvořák V., Dančák M., Dřevojan P. & Wild J. (2017): Distributions of vascular plants in the Czech Republic. Part 4. – Preslia 89: 115–201.
This the fourth part of the series on the distributions of vascular plants in the Czech Republic includes grid maps of 84 taxa of the genera Aldrovanda, Alisma, Asclepias, Azolla, Blechnum, Botrychium, Butomus, Carex, Centaurea, Drosera, Dysphania, Hypochaeris, Illecebrum, Luronium, Ophioglossum, Persicaria, Pilularia, Rubrivena, Sagittaria, Salvinia, Scirpoides, Sideritis, Streptopus, Teesdalia and Thesium. These maps were produced by taxonomic experts based on herbarium specimens, literature and field records. Of the native taxa studied, 40 are on the national Red List. Among them, Carex pseudobrizoides, Hypochaeris glabra and Illecebrum verticillatum are rare species of mainly sandy habitats, which are all now restricted to a few or several sites and are therefore classified as critically threatened. Endangered aquatics and wetland plants are represented by Alisma gramineum, Salvinia natans, three Drosera species, Luronium natans and Pilularia globulifera, of which the latter two are species with sub-Atlantic distributions, reaching in this country their south-eastern and eastern distribution limits, respectively. All eight species of the genus Thesium and most species of Botrychium are endangered, either because they are rare or they are now considerably less common than they were, or combination of both. Two of the species mapped in this paper are now extirpated from this country. Botrychium simplex was last recorded more than 120 years ago, whereas the spontaneous occurrences of Aldrovanda vesiculosa vanished after 1952. However, the latter species has recently been deliberately planted in the wild for conservation purposes. The taxonomically extremely difficult Centaurea sect. Jacea, whose taxonomy and evolution is complicated by polyploidization and frequent hybridization, includes many taxa whose distributions were unclear until recently. Maps of Centaurea species and subspecies based on revised herbarium specimens are given, supplemented with the occurrence of their hybrids in grid cells where the parental species have not been documented. Alien species are mainly species originally introduced into Europe as ornamental and/or medicinal plants, such as Azolla filiculoides, Carex muskingumensis, Rubrivena polystachya, Sagittaria latifolia, three species of Dysphania and two of Persicaria. Another one, Asclepias syriaca, has become locally abundant and invasive. Other aliens were introduced unintentionally, such as Dysphania melanocarpa and D. pumilio with wool from Australia or Persicaria pensylvanica with soybeans from North America. Spatial distributions and temporal dynamics of individual taxa are shown in maps and documented by records included in the Pladias database and available in electronic appendices. The maps are accompanied by comments, which include additional information on the distribution, habitats, taxonomy and biology of the taxa.
 
Kaplan Z., Danihelka J., Lepší M., Lepší P., Ekrt L., Chrtek J. Jr., Kocián J., Prančl J., Kobrlová L., Hroneš M. & Šulc V. (2016): Distributions of vascular plants in the Czech Republic. Part 3. – Preslia 88: 459–544.
The third part of the publication series on the distributions of vascular plants in the Czech Republic includes grid maps of 105 taxa of the genera Acorus, Amelanchier, Asplenium, Calla, Cerastium, Ceratophyllum, Eichhornia, Hieracium, Hippuris, Hottonia, Lemna, Limosella, Peplis, Pistia, Pontederia, Sorbus, Spirodela, Symphytum, Trapa, Valerianella and Wolffia. The maps were produced by taxonomic experts based on all available herbarium, literature and field records. Three of the studied genera include Czech endemics, which are confined to small geographic areas, mostly have small population sizes and thus are of conservation concern. These maps resulted from detailed fieldwork and herbarium revisions by monographers of the respective groups and for many of these endemics they are first available maps. The endemic species of Hieracium occur mainly in the subalpine habitats in the Krkonoše, Králický Sněžník and Hrubý Jeseník Mts. By contrast, a great majority of Sorbus endemics are found mainly in thermophilous open broad-leaved and pine forests on rocky habitats at middle altitudes. Cerastium alsinifolium is confined in its total distribution to serpentine outcrops in western Bohemia. Asplenium is another ecologically specialized group, which includes petrophytes, some of which are restricted to specific substrates, such as siliceous, limestone, basalt or serpentine rocks. The plants studied include 53 taxa classified in the Red List of vascular plants of the Czech Republic, some of which have shown remarkable declines. Symphytum bohemicum, distributed mainly in central Europe, is confined to calcareous fens in the lowlands. There are many endangered and vulnerable species amongst aquatic plants, which are threatened mainly by fish-farming intensification, eutrophication and habitat destruction. Populations of some of the most endangered and attractive aquatics, including Hippuris vulgaris and Trapa natans, have been lost and locally replaced by plants of unknown provenance purchased in garden stores, which causes a potential threat of genetic erosion of native populations. Attractive appearance is the reason why alien aquatics, such as Eichhornia crassipes, Pistia stratiotes and Pontederia cordata, are sometimes planted not only in garden pools but also in wetlands in the countryside; each has been recorded at about a dozen such sites during the past 25 years. Lemna turionifera, by contrast, has been introduced and dispersed by waterfowl and is now widespread in the country. The histories of the introduction and subsequent spread are also described and analysed for the widespread neophyte Acorus calamus and for the alien species of Amelanchier and Symphytum. Spatial distributions and temporal dynamics of individual species are shown in maps and documented by records included in the Pladias database and available in electronic appendices. The maps are accompanied by comments, which include additional information on the distribution, habitats, taxonomy and biology of the species.
 
Kaplan Z., Danihelka J., Štěpánková J., Ekrt L., Chrtek J. Jr., Zázvorka J., Grulich V., Řepka R., Prančl J., Ducháček M., Kúr P., Šumberová K. & Brůna J. (2016): Distributions of vascular plants in the Czech Republic. Part 2. – Preslia 88: 229–322.
The second part of the publication series on the distributions of vascular plants in the Czech Republic includes grid maps of 87 taxa of the genera Antennaria, Aposeris, Astragalus, Avenula, Bidens, Carex, Cenchrus, Centunculus, Convallaria, Crocus, Cryptogramma, Cyperus, Dryopteris, Gladiolus, Gratiola, Helictochloa, Hierochloë, Lindernia, Maianthemum, Myriophyllum, Notholaena, Nymphoides, Radiola, Schoenoplectus, Sisyrinchium, Spergularia, Tillaea, Veratrum and Veronica. The maps were produced by taxonomic experts based on all available herbarium, literature and field records. The plants studied include 56 taxa registered in the Red List of vascular plants of the Czech Republic, some of which showed remarkable declines. Astragalus arenarius, Hierochloë odorata and H. repens, as representatives of vegetation of inland sand dunes, are critically threatened due to conversion of their habitats to arable land, local sand mining, afforestation, changes in landscape management and eutrophication followed by succession. Each of them survives at a few localities and their populations are poor. Competitively weak wetland annuals, confined to open habitats such as exposed fishpond littorals and river beds, abandoned sand-pits and wet arable fields, have considerably declined and disappeared from large areas as a result of agriculture and fish-farming intensification, in particular fertilization and restriction of summer drainage of fishponds, and other changes in land-use. These include Centunculus minimus, Cyperus flavescens, C. michelianus, Lindernia procumbens, Radiola linoides and Tillaea aquatica. Observed recently at a few sites only, they are all classified as critically threatened. A map is for the first time provided also for Spergularia kurkae, a newly recognized species and a central-European endemic. Astragalus asper, Schoenoplectus supinus and Veronica pumila are now extirpated from the country’s flora. In contrast, Spergularia marina, until recently confined to natural saline habitats and very rare, has been spreading along roads that are treated by de-icing salts. Examination of an old herbarium voucher showed that the only record of Astragalus alopecuroides in the Czech flora actually refers to the species whose correct name is A. alopecurus. Further introduced casuals mapped in this paper include Bidens pilosus, Cenchrus echinatus, Gratiola neglecta and Lindernia dubia, each introduced to only a few sites. Bidens connatus was recorded at two dozen sites and appears to have spread as a consequence of the great floods in 2002. Typical examples of naturalized neophytes are Veronica filiformis and V. peregrina, both currently known from many parts of the country. Invasive aliens are represented by Bidens frondosus, which began to spread in the 1930s and now is frequent throughout the country. Spatial and temporal dynamics of individual species are shown in maps and documented by records included in the Pladias database and available in Electronic appendices. The maps are accompanied by comments, which include additional information on distribution, habitats, taxonomy and biology of the species.
 
Aykurt C., Deniz I. G. & Kaplan Z. (2016): Potamogeton acutifolius (Potamogetonaceae) – a new species for the flora of Turkey. – Int. J. Bot. 12: 17–19.
Potamogeton acutifolius is reported as a new species for Turkey. The specimens of the species were collected from Acarlar Freshwater Swamp Forest. Potamogeton acutifolius belongs to a morphologically defined P. compressus group. This species can be easily distinguished from the other species that occur in Turkey especially by its compressed stem, leaves with additional sclerenchymtous strands and short peduncle. Its morphological description, distinguishing characters and systematic placement are given. The new locality discovered in Turkey is the southernmost occurrence of the species in its entire range.
 
Kaplan Z., Danihelka J., Štěpánková J., Bureš P., Zázvorka J., Hroudová Z., Ducháček M., Grulich V., Řepka R., Dančák M., Prančl J., Šumberová K., Wild J. & Trávníček B. (2015): Distributions of vascular plants in the Czech Republic. Part 1. – Preslia 87: 417–500.
Despite a long history of botanical research on the Czech flora and the large amount of data on plant distribution that has been collected, there is still no comprehensive piece of work with distribution maps in this country and no distribution maps are available for more than a half of plant taxa. This paper is the first part of a series of publications prepared within the PLADIAS project, intended as the first step towards a complete atlas of the distribution of both native and alien vascular plants in the Czech Republic. It contains grid distribution maps of 75 taxa of the genera Achillea, Aegilops, Aira, Alopecurus, Avena, Bolboschoenus, Carex, Cladium, Elatine, Eleocharis, Eriophorum, Glyceria, Polypogon, Sclerochloa, Scheuchzeria, Sparganium, Tofieldia, Tragus and Viola. The maps are based on all available herbarium, literature and field records, which were stored at the CzechDistrib database, checked geographically and evaluated taxonomically, and shown in maps using the Central European mapping grid template derived from quadrants of 5 × 3 arc minutes (corresponding to approximately 5.5 × 5.9 km). Many of these maps resulted from detailed revisions carried out during the work on the Flora of the Czech Republic. Maps of taxonomically difficult groups are based solely or mainly on herbarium specimens revised by taxonomic experts. If useful, recent versus old records, native versus alien occurrences, or records based on revised herbarium specimens versus all other records are distinguished using different symbols. Records used for producing maps are listed in electronic appendices. The maps are accompanied by texts that include an outline of general distribution, information on habitats and specific details on the distribution in the country. Where appropriate, comments on taxonomy, biology or spatial and temporal dynamics in distribution are given.
 
Kolář F., Kaplan Z., Suda J. & Štech M. (2015): Populations of Knautia in ecologically distinct refugia on the Hercynian massif belong to two endemic species. – Preslia 87: 363–386.
Comprehensive taxonomic studies in which a combination of molecular, cytogenetic, morphological and ecological approaches are used have resulted in remarkable discoveries even in well-known floras. In particular, recognition of new local endemics has important implications for conservation and management of plant diversity. Due to Quaternary climatic oscillations, the vascular flora of the Czech Republic only includes a few endemic taxa, usually microspecies with an apomictic mode of reproduction. Here we re-evaluate the taxonomy of Knautia arvensis, an intricate eco-geographically differentiated diploid-polyploid complex, and identify two new sexual species endemic to central Europe, which were previously included in the polymorphic K. arvensis. While K. serpentinicola Smejkal ex Kolář, Z. Kaplan, J. Suda et Štech is a diploid and tetraploid species restricted to four isolated serpentine areas in the Czech Republic and Germany, diploid K. pseudolongifolia (Szabó) Żmuda is known from a single subalpine site in the Krkonoše Mts. Our investigation of 38 populations of K. arvensis s. str. and the two newly recognized species sampled across eastern central Europe revealed a distinct yet incomplete (i.e. confounded by phenotypic plasticity) morphological differences between the three species. These results together with available data on cytological (distinct nuclear genome size), genetic (independent evolutionary histories) and ecological (distinct ecological preferences) variation support an independent taxonomic status for the newly described species. Our study highlights the importance of ecologically stable habitats where plant competition is not severe (Holocene refugia) for preserving unique plant diversity. In addition, it demonstrates the value of multi-disciplinary taxonomic research even in botanically well-known areas.
 
Lastrucci L., Viciani D., Foggi B., Miranda S., Santangelo A. & Kaplan Z. (2015): Typification of two species names of Potamogeton (Potamogetonaceae). – Phytotaxa 222: 72–74.
Two species names of the genus Potamogeton Linnaeus are typified: P. panormitanus Biv. and P. tuberculatus Ten. & Guss. Potamogeton panormitanus is considered as a synonym of P. pusillus L. and P. tuberculatus as a synonym of P. trichoides Cham. & Schltdl.
 
Prančl J., Kaplan Z., Trávníček P. & Jarolímová V. (2014): Genome size as a key to evolutionary complex aquatic plants: polyploidy and hybridization in Callitriche (Plantaginaceae). – PLoS ONE 9(9): e105997.
Despite their complex evolutionary histories, aquatic plants are highly underrepresented in contemporary biosystematic studies. Of them, the genus Callitriche is particularly interesting because of such evolutionary features as wide variation in chromosome numbers and pollination systems. However, taxonomic difficulties have prevented broader investigation of this genus. In this study we applied flow cytometry to Callitriche for the first time in order to gain an insight into evolutionary processes and genome size differentiation in the genus. Flow cytometry complemented by confirmation of chromosome counts was applied to an extensive dataset of 1077 Callitriche individuals from 495 localities in 11 European countries and the USA. Genome size was determined for 12 taxa. The results suggest that many important processes have interacted in the evolution of the genus, including polyploidization and hybridization. Incongruence between genome size and ploidy level, intraspecific variation in genome size, formation of autotriploid and hybridization between species with different pollination systems were also detected. Hybridization takes place particularly in the diploid – tetraploid complex C. cophocarpaC. platycarpa, for which the triploid hybrids were frequently recorded in the area of co-occurrence of its parents. A hitherto unknown hybrid (probably C. hamulata × C. cophocarpa) with a unique chromosome number was discovered in the Czech Republic. However, hybridization occurs very rarely among most of the studied species. The main ecological preferences were also compared among the taxa collected. Although Callitriche taxa often grow in mixed populations, the ecological preferences of individual species are distinctly different in some cases. Anyway, flow cytometry is a very efficient method for taxonomic delimitation, determination and investigation of Callitriche species, and is even able to distinguish homoploid taxa and identify introduced species.
 
Kaplan Z., Šumberová K., Formanová I. & Ducháček M. (2014): Re-establishment of an extinct population of the endangered aquatic plant Potamogeton coloratus. – Aquatic Bot. 119: 91–99.
Persistent soil seed banks play a key role in preventing extirpation of plants during periods of temporarily unsuitable conditions. They can serve as effective tools in achieving the goal of restoring wetland vegetation. Potamogeton coloratus, an aquatic plant of shallow, calcareous waters, has become critically endangered or vanished in large regions of its mainly European range. In the Czech Republic, it was observed in 1977 for the last time (prior to our restoration project) and has been classified as an extinct species. We successfully re-established one population of it, and also established a new one, both located in a fen complex from which it has been absent for more than 30 years. One population was restored in a desilted pool in which the species had occurred previously; the other was established in a newly created pool by means of transferring soil, including the seed bank, from a pool in which the species formerly occurred. Monitoring of these sites over subsequent years confirmed establishment and increase of the populations. Along with the target species, other rare, native aquatic plants (e.g. Utricularia vulgaris and Chara hispida) were found growing in the newly created pool. Propagules of these species were also detected in the sediment collected in the old pool prior the desilting and subjected to soil seed bank analysis. Although altogether 26 plant species were identified in the soil seed bank, no propagules of P. coloratus were detected, most likely due to their small number in the sediment analyzed.
 
Kaplan Z., Jarolímová V. & Fehrer J. (2013): Revision of chromosome numbers of Potamogetonaceae: a new basis for taxonomic and evolutionary implications. – Preslia 85: 421–482.
In order to establish a sound basis for systematic and evolutionary research, we determined the chromosome numbers of 181 samples of 47 species and 32 hybrids of Potamogetonaceae from 27 countries and areas, ranging from Greenland in the north to New Zealand in the south and reevaluated previously published counts. The first counts are reported here for 10 species and 25 hybrids of Potamogeton and for 1 species and 3 hybrids of Stuckenia. Both homoploid and heteroploid hybrids were identified, as well as hybrids resulting from the fusion of reduced and unreduced gametes. Three previously undetected hybrids of Potamogeton are described and validated as P. ×drepanoides, P. ×luxurians and P. ×serrulifer. The extensive within-species variation in chromosome numbers sometimes reported in the literature was not confirmed. Chromosome numbers appeared to be generally species-specific in Potamogetonaceae; the only exceptions were two sterile autotriploid plants detected within two otherwise fertile diploid Potamogeton species. Furthermore, chromosome numbers were often uniform even within species groups or genera and to some degree also clade-specific in phylogenetic trees based on nuclear ribosomal markers (ITS and 5S-NTS regions). In the largest genus, Potamogeton, there are two base numbers for diploids (x = 13 and x = 14) and three ploidy levels in species (diploids, tetraploids and octoploids; all polyploids were based on x = 13), in Stuckenia only hexaploids (also based on x = 13) occur and Groenlandia is monotypic with x = 15. A critical evaluation of the published counts revealed three major sources of error: (i) methodological problems due to difficult karyotypes, (ii) approximations based on wrong preconceptions and (iii) poor taxonomic treatments, misidentified species or unrecognized hybrids. We estimate that about 24% of the counts in original publications and up to 41% in chromosome atlases and indices are doubtful or demonstrably erroneous. Most of these were from a relatively few dubious sources whereas the majority of counts reported in the literature correspond to our findings. Two alternative scenarios for the evolution of chromosome numbers in this family are discussed in a phylogenetic context, with either x = 13 or x = 14 as the base chromosome number in the family; the base number of x = 7 suggested by some authors is refuted. In both scenarios, several aneuploid transitions between these karyotypes and a single change towards x = 15 have to be assumed. Polyploidizations are rare in this family and mostly associated with major evolutionary events. A single or a very few events led to a large species group of tetraploids in Potamogeton, and two subsequent rounds of polyploidization can explain the cytotype of Stuckenia, in which speciation took place entirely at the hexaploid level. Three octoploid species of Potamogeton had allopolyploid origins. This study gives an example of how the careful re-examination of chromosome numbers can substantially ameliorate interpretations of systematic and phylogenetic patterns.
 
Kaplan Z. & Fehrer J. (2013): Molecular identification of hybrids from a former hot spot of Potamogeton hybrid diversity. – Aquatic Bot. 105: 34–40.
More than a century ago, an extremely high diversity of Potamogeton hybrids was recorded in several rivers and streams in Jutland, Denmark. Accuracy of their identification was doubted by some later authors who were sceptical about the existence and co-occurrence of so many hybrids. Selected original localities were investigated for the presence of morphologically matching plants after more than 100 years. In spite of profound changes in landscape and considerable deterioration of aquatic habitats during the 20th century resulting in a significant decline of submerged vegetation, three of ten previously recorded hybrids were recently found that had persisted at their original localities. Two of them, whose existence had not been proved previously, were subjected to molecular analyses. RFLP, direct sequencing and cloning of the ITS region confirmed their previous morphological identification: P. × undulatus as P. crispus × P. praelongus and P. × cognatus as P. perfoliatus × P. praelongus. Chloroplast DNA sequencing identified P. praelongus as the maternal parent in both crosses. The existence of most of the other hybrid combinations recorded from Jutland was proved by means of molecular analyses conducted on plants from other regions. Their morphologies perfectly correspond to old herbarium vouchers from Jutland and support their original identifications. These observations indicate that Jutland rivers and streams hosted a high species and hybrid diversity still in the late 19th century, but most of this richness has meanwhile disappeared.
 
Kaplan Z. & Marhold K. (2012): Multivariate morphometric analysis of the Potamogeton compressus group (Potamogetonaceae). – Bot. J. Linn. Soc. 170: 112–130.
The Potamogeton compressus group is a complex of three to five closely related species with a circumpolar distribution in the Northern Hemisphere. Multivariate morphometric analyses (principal component analysis, cluster analysis, canonical and classificatory discriminant analyses) were used to elucidate the patterns of variation within this group and to test the morphological differentiation of the species recognized in the current literature. From the entire distribution range, 156 specimens of the group were included in the numerical methods. Results from morphological comparison are discussed in relation to molecular data, reproductive behaviour and geographical distribution. Morphometric analyses provided evidence that this complex can be clearly divided into three groups, one of which was subdivided mainly on the basis of allopatric occurrence and genetic differentiation. These groups correspond to four species accepted here: P. acutifolius (temperate regions of Europe), P. compressus (boreal and temperate regions of Europe and Asia), P. manchuriensis (northeastern China and Russian Far East) and P. zosteriformis (boreal and temperate regions of North America). Two species, P. acutifolius and P. compressus, are partly sympatric, but clearly differentiated morphologically and genetically, and effectively isolated reproductively. Endemic P. manchuriensis is characterized by a unique combination of characters and an occurrence in a limited geographical area. Allopatric P. zosteriformis is weakly differentiated morphologically from P. compressus, but differs markedly in molecular markers correlated with geographical differentiation. It may represent a cryptic species. In contrast, a recently suggested concept of southern Siberian P. henningii was not supported by our analyses. Plants so named are considered here as slender phenotypes of the widespread and variable P. compressus.
 
Kaplan Z. (2012): Flora and phytogeography of the Czech Republic. – Preslia 84: 505–573.
A review of the flora and phytogeography of the Czech Republic is given. The diversity of plants in this country reflects its geographic position in the centre of Europe, local natural conditions and the effect of intense human activity on the landscape. The Czech flora includes 148 families, 916 genera, 3557 species (plus 194 additional subspecies) and 609 hybrid vascular plants. Families richest in species are Asteraceae (662 species), Rosaceae (316), Poaceae (275), Fabaceae (170), Brassicaceae (148), Cyperaceae (127), Lamiaceae (112), Caryophyllaceae (108) and Apiaceae (100). Most of these species are native and 36.0% are alien. The spectrum of life-forms is dominated by hemicryptophytes (45.7%), followed by therophytes (22.3%), phanerophytes (14.4%), geophytes (9.3%), chamaephytes (5.1%) and hydrophytes (3.2%), while the percentage of epiphytes is negligible (only two species). Several species that occur in the Czech Republic are relicts from glacial and early postglacial periods. Examples of arctic, boreal, alpine, steppe and other sorts of relicts are listed. Because of the relatively small size of this country and the considerable climatic and vegetational changes caused by glaciations, which repeatedly eliminated the local flora, endemism is relatively low in the Czech Republic. All endemics are of Quaternary age (neoendemics). A revised list of endemic species and subspecies includes 74 taxa endemic to the Czech Republic and adjacent border regions, which is 2% of the total vascular plant diversity. Of these, 48 taxa are strictly Czech endemics (defined by the borders of the country), the distributions of the other 26 taxa extend slightly beyond the borders of this country (mostly by less than 1 km) in the summit areas of the Krkonoše/Karkonosze Mts and/or in the Králický Sněžník/Śnieżnik Kłódzki Mts. Hieracium and Sorbus are the genera with the greatest number of endemics (25 and 11 species and subspecies, respectively). Patterns in the distribution and occurrence of endemics in different types of habitat are discussed. The greatest concentration of endemics is in the Krkonoše Mts, where they occur mostly in subalpine habitats, such as natural grasslands above the timberline, summit rocks and rocky slopes, and various sites in glacial cirques including avalanche tracks. Other endemics of subalpine habitats occur in the Králický Sněžník Mts and Hrubý Jeseník Mts. Endemics at low altitudes mostly occur on rocky outcrops and in associated open thermophilous forests and grasslands, less frequently on open sandy areas, in fens and various types of forest. Maps of the distribution of endemics in the Czech Republic are presented. The majority of Czech endemics are rare and/or strongly endangered and included on the Red List of the Czech flora, and seven are extinct or missing. Changes in understanding of Czech endemics are reviewed and evolution of endemics discussed. The Czech Republic is situated at the intersection of several important European migration routes. The Czech flora is composed of almost all the floristic elements that occur in central Europe of which the Central-European geoelement is dominant. Other well represented geoelements include the Central-European-(sub-)alpine, Arctic-alpine, Boreal, Sub-boreal, Sub-Atlantic, Sub-Mediterranean, Pontic, Sub-pontic and South-Siberian. Examples of all geoelements are listed. The limits of the distributions of a number of widespread species are in the Czech Republic. These species are distinguished as boundary or outlying elements. Examples of species that in the Czech Republic are at the limits of their distributions, which range in different directions, are listed. Groups of species with similar ecogeographic features within the Czech Republic are distinguished as regional types of distribution (phytochorotypes). 15 basic phytochorotypes are listed, defined and illustrated using maps. Phytogeographical division of the Czech Republic is described. Three principal phytogeographical regions are recognized within the country, which are based on the dominant flora and vegetation that reflects specific regional topography and climatic conditions. These regions are further subdivided into phytogeographical provinces, districts and subdistricts. All of these phytogeographical units (phytochoria) are listed and their position illustrated on a map.
 
Danihelka J., Chrtek J. Jr. & Kaplan Z. (2012): Checklist of vascular plants of the Czech Republic. – Preslia 84: 647–811.
A checklist of vascular plants of the Czech Republic is provided, based on the Kubát et al’s Key to the flora of the Czech Republic from 2002 and volumes 7 and 8 of the Flora of the Czech Republic as taxonomic reference, and incorporating numerous floristic, taxonomic and nomenclatural novelties. Native, alien, both naturalized and casual, as well as frequently cultivated taxa are included. Species, subspecies, nothospecies and nothosubspecies, and some frequently used variety names are listed. For cultivated plants, the taxonomic rank of Group is widely applied. For practical purposes, 188 species aggregates and other informal species groups are defined. References are made to corresponding taxonyms in the Key or the two Flora volumes when name or orthography changes occurred. Most important changes in nomenclature, taxonomy, recently described taxa and additions to the country’s flora are annotated. The flora of the Czech Republic includes 3557 species (plus 194 additional subspecies) and 609 (plus 13 additional nothospecies) hybrids. Of these, 2256 species are native, 464 naturalized (228 archaeophytes and 236 neophytes) and 837 casual aliens. Further, 324 cultivated taxa of different ranks are listed. The list includes categorizations of alien species of Pyšek et al.’s second edition of the Catalogue of alien plants of the Czech Republic and Red List categorizations of Grulich’s third edition of the Red List of vascular plants of the Czech Republic, both published in Preslia in 2012.
 
Pyšek P., Danihelka J., Sádlo J., Chrtek J. Jr., Chytrý M., Jarošík V., Kaplan Z., Krahulec F., Moravcová L., Pergl J., Štajerová K. & Tichý L. (2012): Catalogue of alien plants of the Czech Republic (2nd edition): checklist update, taxonomic diversity and invasion patterns. – Preslia 84: 155–255.
A complete list of all alien taxa ever recorded in the flora of the Czech Republic is presented as an update of the original checklist published in 2002. New data accumulated in the last decade are incorporated and the listing and status of some taxa are reassessed based on improved knowledge. Alien flora of the Czech Republic consists of 1454 taxa listed with information on their taxonomic position, life history, geographic origin (or mode of origin, distinguishing anecophyte and hybrid), invasive status (casual; naturalized but not invasive; invasive), residence time status (archaeophyte vs neophyte), mode of introduction into the country (accidental, deliberate), and date of the first record. Additional information on species performance that was not part of the previous catalogue, i.e. on the width of species’ habitat niches, their dominance in invaded communities, and impact, is provided. The Czech alien flora consists of 350 (24.1%) archaeophytes and 1104 (75.9%) neophytes. The increase in the total number of taxa compared to the previous catalogue (1378) is due to addition of 151 taxa and removal of 75 (39 archaeophytes and 36 neophytes), important part of the latter being the reclassification of 41 taxa as native, mostly based on archaeobotanical evidence. The additions represent taxa newly recorded since 2002 and reported in the national literature; taxa resulting from investigation of sources omitted while preparing the previous catalogue; redetermination of previously reported taxa; reassessment of some taxa traditionally considered native for which the evidence suggests the opposite; and inclusion of intraspecific taxa previously not recognized in the flora. There are 44 taxa on the list that are reported in the present study for the first time as aliens introduced to the Czech Republic or escaped from cultivation: Abies concolor, A. grandis, A. nordmanniana, Avena sterilis subsp. ludoviciana, A. ×vilis, Berberis julianae, B. thunbergii, Bidens ferulifolius, Buddleja alternifolia, Buglossoides incrassata subsp. splitgerberi, Buxus sempervirens, Corispermum declinatum, Cotoneaster dielsianus, C. divaricatus, Euphorbia myrsinites, Gleditsia triacanthos, Helleborus orientalis, Hieracium heldreichii, Koelreuteria paniculata, Lonicera periclymenum, Lotus ornithopodioides, Malus baccata, M. pumila, Miscanthus sacchariflorus, Morus alba, Muscari armeniacum, Paeonia lactiflora, Pennisetum alopecuroides, Pinguicula crystallina subsp. hirtiflora, P. grandiflora subsp. rosea, Podophyllum hexandrum, Pyracantha coccinea, Rhodotypos scandens, Rumex patientia × R. tianschanicus ‘Uteuša’, Salix cordata, Sarracenia purpurea, Sasa palmata ‘Nebulosa’, Scolymus maculatus, Spiraea japonica, Tagetes tenuifolia, Thuja occidentalis, Trifolium badium, Vaccinium corymbosum and Viburnum rhytidophyllum. All added and deleted taxa are commented on. Of the total number of taxa, 985 are classified as casuals, 408 as naturalized but not invasive, and 61 as invasive. The reduction in the number of invasive taxa compared to the previous catalogue is due to a more conservative approach adopted here; only taxa that currently spread are considered invasive. Casual taxa are strongly overrepresented among neophytes compared to archaeophytes (76.7% vs 39.4%), while naturalized but non-invasive taxa follow the reversed pattern (18.8% vs 57.4). However, these two groups do not significantly differ in the proportion of invasive taxa. Of introduced neophytes, 250 taxa (22.6%) are considered vanished, i.e. no longer present in the flora, while 23.3% became naturalized, and 4.5% invasive. In addition to the traditional classification based on introduction–naturalization–invasion continuum, taxa were classified into 18 population groups based on their long-term trends in metapopulation dynamics in the country, current state of their populations, and link to the propagule pressure from cultivation. Mapping these population groups onto the unified framework for biological invasions introduced by Blackburn et al. in 2011 made it possible to quantify invasion failures, and boom-and-busts, in the Czech alien flora. Depending on inclusion criteria (whether or not extinct/vanished taxa and hybrids are considered), alien taxa ever recorded in the Czech Republic contribute 29.7–33.1% to the total country’s plant diversity; taking into account only naturalized taxa, a permanent element of the country’s flora, the figure is 14.4–17.5%. Analysis of the dates of the first record, known for 771 neophytes, indicates that alien taxa in the flora have been increasing at a steady pace without any distinct deceleration trend; by extrapolating this data to all 1104 neophytes recorded it is predicted that the projected number would reach 1264 in 2050. Deliberate introduction was involved in 747 cases (51.4%), the remaining 48.6% of taxa are assumed to have arrived by unintentional pathways. Archaeophytes are more abundant in landscapes, occupy on average a wider range of habitat types than neophytes, but reach a lower cover in plant communities. The alien flora is further analysed with respect to representation of genera and families, origin and life history.
 
Aymerich P., Kaplan Z., Guardiola M., Petit A. & Schwarzer U. (2012): Potamogeton schweinfurthii in the Iberian Peninsula. – Anales Jard. Bot. Madrid 69: 187–192.
We provide the first records for the Iberian Peninsula of Potamogeton schweinfurthii A. Benn., a species distributed mainly in Africa that was not discovered in Europe until 2005, where it is assumed to be indigenous but it has generally been confused with P. lucens. The Iberian specimens, which for the most part are from recent collections, have been identified based on morphological characteristics and molecular studies. We have detected 8 localities, 4 in the northeastern area of the Peninsula (Catalonia and Navarra) and 4 from the West (south and north of Portugal and western Andalusia). Our studies show that it is a very rare species on a regional level. Although it is a mainly tropical and subtropical species, we have found that P. schweinfurthii (both natural populations and those cultivated) has a high tolerance to climates with severe winters and frequent frosts. The large proportion of populations found in anthropogenic habitats, and the fact that most European records are from the past half-century, suggest that P. schweinfurthii may have experienced a recent expansion favoured by the construction of large number of artificial water bodies in the Mediterranean region. This raises the possibility that P. schweinfurthii in Europe is a species that forms temporary populations and has a naturally unstable area.
 
Kaplan Z. & Uotila P. (2011): Potamogeton × exilis (P. alpinus × P. natans), a new hybrid pondweed from Finland. – Nord. J. Bot. 29: 477–483.
A Potamogeton hybrid recently discovered in Finland was proven to be a new taxon, which has a different parentage than the most similar P. × vepsicus ( = P. natans × praelongus) described from Russia. Based on molecular and morphological investigation, the new hybrid was identified as P. alpinus × natans and is here described as P. × exilis nothosp. nov. The hybrid is known only from several nearby localities in a single river system. All discovered colonies almost certainly originate from a single hybridization event that occurred in the upper part of the river system. Other localities downstream have been established through fragmentation and dispersal of stems and rhizomes of this sterile hybrid. A detailed morphological comparison of the new hybrid with similar hybrids and species is provided.
 
Kaplan Z. & Fehrer J. (2011): Erroneous identities of Potamogeton hybrids corrected by molecular analysis of plants from type clones. – Taxon 60: 758–766.
Hybridization is one of the main sources of taxonomic complexity in Potamogeton. In spite of long and intensive research, the total hybrid diversity and distribution of many hybrids are still insufficiently known. Identities of two currently recognized hybrids were tested using molecular analyses of plants from the original clones growing at the type localities of their correct names. Additive characters in direct sequencing of the ITS region and the placement of cloned sequences in a Bayesian consensus tree were used to identify the exact identity of these hybrids. Potamogeton ×lanceolatifolius is widely recognized as a hybrid P. gramineus × P. polygonifolius. However, the molecular analyses and cytological investigation identified this Swedish hybrid as P. gramineus × P. nodosus although P. nodosus currently does not occur in the whole of Scandinavia. This hybrid provides some insight into the former distribution area of P. nodosus as affected by past climatic changes. The recently detected P. ×vepsicus was originally described as P. alpinus × P. natans but the molecular investigation revealed that its correct identity is P. natans × P. praelongus. In both cases, the actual identities could hardly have been unequivocally deduced from the morphology of the hybrids. The existence of these hybrid combinations is here confirmed for the first time. The maternally inherited chloroplast rpl20-5'rps12 sequences were used to identify the female parental species. The name “P. ×argutulus”, previously, but erroneously, used for a hybrid P. gramineus × P. nodosus, is typified and reduced to the synonymy of P. gramineus.
 
Kaplan Z., Fehrer J. & Hellquist C. B. (2011): Potamogeton ×jacobsii (Potamogetonaceae) from New South Wales, Australia – the first Potamogeton hybrid from the Southern Hemisphere. – Telopea 13: 245–256.
Although more than 80 hybrids are documented for Potamogeton in the Northern Hemisphere, the hybrid diversity in the Southern Hemisphere is largely unknown. A taxonomically uncertain Potamogeton plant discovered in New South Wales, Australia, was subjected to detailed morphological investigation and molecular analyses to discover its exact identity. Both approaches resulted in the identification of the Potamogeton specimen as P. crispus × P. ochreatus, which is a previously unrecorded hybrid and is here described as Potamogeton ×jacobsii nothosp. nova. Although P. crispus is known to hybridise with many other species, P. ×jacobsii is the first known hybrid involving P. ochreatus.
 
Kaplan Z. (2010): Tiselius’ Potamogeton exsiccates: changes in taxonomy and nomenclature from one-century perspective. – Ann. Bot. Fennici 47: 373–393.
Tiselius’ outstanding collection Potamogetones suecici exsiccati is reviewed and re-evaluated from the viewpoint of the present nomenclature and taxonomy. All 150 gatherings issued in this collection are listed and interpreted taxonomically. In a few cases new taxonomic findings are given based on molecular investigation of plant material from the type localities. All new names proposed in this collection are listed and checked for their nomenclatural validity and legitimacy. Lectotypes are designated for 64 valid names and authentic specimens listed for 27 additional invalid designations. Two names (and their types) are of particular importance for contemporary plant taxonomy because these are the correct names for recognized and confirmed Potamogeton hybrids: P. × torssanderi for the triple hybrid P. gramineus × P. lucens × P. perfoliatus and P. × lanceolatifolius for P. gramineus × P. nodosus.
 
Kaplan Z. (2010): Hybridization of Potamogeton species in the Czech Republic: diversity, distribution, temporal trends and habitat preferences. – Preslia 82: 261–287.
A revision of the diversity and distribution of Potamogeton hybrids in the Czech Republic is presented. Thorough examination of herbarium material and recent extensive field studies revealed the present and/or past occurrence of eight Potamogeton hybrids in the Czech Republic. In addition to morphological characters, stem anatomy and/or molecular analysis were used to identify some of the hybrids. All the hybrids detected are between broad-leaved species of the genus, suggesting that hybrids between linear-leaved species may be overlooked because of the overall morphological similarity of taxa within this group. Four of the hybrids identified, P. ×nitens, P. ×olivaceus, P. ×sparganiifolius and P. ×undulatus, are recorded for the first time from the Czech Republic. Four of the hybrids are now extinct in the Czech Republic and the extant hybrids are rare. The occurrence of P. ×lintonii was not confirmed; the previous record was based on extreme forms of P. gramineus. The name P. ×concinnitus, proposed for a putative hybrid combination “P. pusillus × P. crispus”, was lectotypified and reduced to a synonym of P. crispus. Although the absolute number of finds of specimens of Potamogeton hybrids per decade is increasing, this is not a result of more frequent hybridization but of an increase in recording activity. Most records for recent decades are associated with targeted research by a few experts. The typical habitat of Potamogeton hybrids in the Czech Republic are ponds that were previously drained in summer and allowed to dry out. Many historical localities disappeared when the traditional fishpond management was largely abandoned and fish farming become more intensive. In the 19th century in particular some hybrids were recorded also in rivers but these occurrences generally disappeared after the extensive channelling of rivers at the beginning of the 20th century. Many hybrids occur at the same localities as their parents but it is documented that hybrids can persist vegetatively in the absence of the parental species, presumably as relics of the previous presence of the parent plants. Although almost all Potamogeton hybrids are consistently sterile, a cultivation experiment showed that P. ×angustifolius set seeds that were fertile and successfully produced adult plants.
 
Zalewska-Gałosz J., Ronikier M. & Kaplan Z. (2010): Discovery of a new, recurrently formed Potamogeton hybrid in Europe and Africa: Molecular evidence and morphological comparison of different clones. – Taxon 59: 559–566.
A new Potamogeton hybrid resulting from crossing between P. nodosus and P. perfoliatus, and occurring in Europe and Africa is described here as P. ×assidens. The hybrid identity was unequivocally confirmed by molecular study of ITS and selected chloroplast DNA regions. In European populations, for which the maternal taxon was identified based on cpDNA as P. nodosus, maternally driven expression of characters may account to a large degree for shaping the range of morphological variability of the hybrid taxon. This was accompanied by a matroclinal concerted evolution observed at the molecular level in the ITS sequences. Our observations may suggest the presence of some genetic mechanisms that promote a higher impact of the maternal lineage on the expression and evolution of the hybrid variability both at the molecular (direction of concerted evolution in hybrids) and the morphological level. Distinctive characters of P. ×assidens and other morphologically close Potamogeton hybrids are discussed. The hybrid most similar to P. ×assidens, namely P. ×rectifolius, is typified.
 
Lastrucci L., Frignani F. & Kaplan Z. (2010): Potamogeton schweinfurthii and similar broad-leaved species in Italy. – Webbia 65: 147–160.
Potamogeton schweinfurthii A. Benn is recorded for the first time from peninsular Italy. This species was recently recorded from Sardinia and other Mediterranean islands, where it was confused with some other similar broad-leaved species of Potamogeton, in particular with P. lucens. The finding of P. schweinfurthii in two Tuscan localities (C Italy) initiated an investigation to verify the presence of further specimens of this plant among the material of similar Potamogeton species (P. lucens, P. alpinus, P. nodosus, P. gramineus) preserved in the main Italian herbaria. The herbarium survey allowed discovery of P. schweinfurthii also in Marche and Apulia regions. The distribution in Italy of four other similar Potamogeton species is specified through the herbarium investigation.
 
Kaplan Z. (2010): New species of aquatic plants for Slovakia. – Bull. Slov. Bot. Spoločn. (Bratislava) 32: 53–58.
Four species of aquatic plants are recorded as new for Slovakia here. All were discovered in revised herbarium material. Potamogeton compressus was collected only once in central Slovakia in 1860 and it is extinct now. Potamogeton obtusifolius is known from three sites in the Eastern-Slovakia lowland; it was last collected in 1975 and is presumably extinct. Although Callitriche hamulata is only known from two collections so far, it is expected to be more frequent but not correctly distinguished from other Callitriche species. An American species Najas guadalupensis was found at two sites escaped from aquarium cultivations or rather intentionally planted in the wild.
 
Kaplan Z., Fehrer J. & Hellquist C. B. (2009): New hybrid combinations revealed by molecular analysis: The unknown side of North American pondweed diversity (Potamogeton). – Syst. Bot. 34: 625–642.
The occurrence and diversity of Potamogeton hybrids was investigated in eastern North America, the region of the highest diversity of Potamogeton species in the world. For various reasons, however, the existence of hybrids in this area has been largely overlooked. ITS direct sequencing and RFLPs revealed four previously unknown hybrids, which are described as Potamogeton ×aemulans (P. bicupulatus × P. epihydrus), P. ×mirabilis (P. gramineus × P. oakesianus), P. ×versicolor (P. epihydrus × P. perfoliatus), and P. ×absconditus (P. perfoliatus × P. richardsonii). These are the first confirmed hybrids involving P. bicupulatus, P. epihydrus, P. oakesianus, and P. richardsonii. Another hybrid, P. ×nitens (P. gramineus × P. perfoliatus), is for the first time confirmed for North America with molecular markers. The hybrids’ maternal parents were revealed by cpDNA sequencing. Phenotypically, two of the hybrids more closely resemble other taxa than their parents. Hybrid diversity and recognition in North America and in Europe are compared. Morphological versus molecular identification of hybrids, occurrence of hybrids in the absence of their parents, parental species relationships, long-term persistence of hybrid clones, vegetative dispersal, frequency of hybridization events, and hybrid distribution patterns are discussed.
 
Kaplan Z. & Fehrer J. (2009): An orphaned clone of Potamogeton ×schreberi in the Czech Republic. – Preslia 81: 387–397.
A Potamogeton hybrid found growing in the absence of parental species in a South Bohemian stream, Czech Republic, was subjected to molecular analyses to identify its exact identity. RFLP of the ITS region confirmed its previous morphological identification as P. natans × P. nodosus (= P. ×schreberi). A comparison of its RFLP pattern with those of P. gramineus, P. lucens and P. polygonifolius unambiguously excluded the possibility that the investigated plants are specimens of other similar hybrids (P. ×fluitans, P. ×sparganiifolius, P. ×gessnacensis). The discovery of P. ×schreberi in South Bohemia is the first record of this hybrid for the Czech Republic. So far, it is known only from five countries and the Czech clone is one of a few extant clones of this hybrid in Central Europe. Chloroplast DNA sequencing identified P. nodosus as the maternal parent although at present this species neither occurs at the locality, nor upstream, nor in the entire drainage basin. The other species, P. natans, only occurs downstream of the locality in isolated side pools in a former stream bed and fishponds in an adjacent drainage basin. The available data indicate that this hybrid has persisted vegetatively at this locality for some time in the absence of its parents.
 
Zalewska-Gałosz J., Ronikier M. & Kaplan Z. (2009): The first European record of Potamogeton ×subobtusus identified using ITS and cpDNA sequence data. – Preslia 81: 281–292.
A combined study of morphology, stem anatomy and DNA sequencing data (nuclear ribosomal ITS region and rpl32-trnL and rps12-rpl20 intergenic spacers of chloroplast DNA) was used to identify a putative Potamogeton hybrid from a river in NE Poland. Based on the morphological and anatomical characters the plants were tentatively identified as P. ×subobtusus Hagstr., a hybrid between P. alpinus Balb. and P. nodosus Poir. This identification was independently confirmed by the presence in hybrid individuals of an additive ITS sequence pattern from these two parental species. In all plants peaks corresponding to nucleotide states of both parents were clearly distinguishable, however the variants from P. nodosus dominated over those from P. alpinus. P. nodosus was also identified as the maternal parent of the hybrid based on cpDNA data and dominated the expression of morphological features in hybrid individuals. A detailed morphological description of P. × subobtusus and the typification of the name are provided. As P. nodosus rarely hybridizes with other species, existence of other hybrids, as well as possible difficulties in recognizing these taxa are also discussed.
 
Kaplan Z. (2008): A taxonomic revision of Stuckenia (Potamogetonaceae) in Asia, with notes on the diversity and variation of the genus on a worldwide scale. – Folia Geobot. 43: 159–234.
A taxonomic revision of the Asian species of Stuckenia, a segregate of Potamogeton, is presented. Six species are recognized and their morphological descriptions, nomenclature and typification of relevant names are given. Distributions of all species are described and lists of representative specimens and distribution maps provided. Lectotypes are designated for 24 names and nomenclatural types are listed for 22 additional names. The correct name for the species known as Potamogeton recurvatus is Stuckenia pamirica (Baagöe) Z. Kaplan, comb. nova. Morphological variation at different levels within the genus is described and compared with different concepts of its taxonomic interpretation. Instructions on examination of key characters are given, together with a key to species. Colour photographs illustrate the general appearance of species as well as many identification details. The pattern of variation and taxonomic validity of the Siberian morphotypes S. subretusa and S. austrosibirica are analyzed. The plasticity of diagnostic characters of P. juncifolius and of P. helveticus from the European Alps, the infraspecific classification of S. filiformis in North America, and the taxonomic status of S. punensis described from Peru are also discussed.
 
Kaplan Z. & Fehrer J. (2007): Molecular evidence for a natural primary triple hybrid in plants revealed from direct sequencing. – Ann. Bot. 99: 1213–1222.
Molecular evidence for natural primary hybrids composed of three different plant species is very rarely reported. An investigation was therefore carried out into the origin and a possible scenario for the rise of a sterile plant clone showing a combination of diagnostic morphological features of three separate, well-defined Potamogeton species. The combination of sequences from maternally inherited cytoplasmic (rpl20-rps12) and biparentally inherited nuclear ribosomal DNA (ITS) was used to identify the exact identity of the putative triple hybrid. Direct sequencing showed ITS variants of three parental taxa, P. gramineus, P. lucens and P. perfoliatus, whereas chloroplast DNA identified P. perfoliatus as the female parent. A scenario for the rise of the triple hybrid through a fertile binary hybrid P. gramineus × P. lucens crossed with P. perfoliatus is described. Even though the triple hybrid is sterile, it possesses an efficient strategy for its existence and became locally successful even in the parental environment, perhaps as a result of heterosis. The population investigated is the only one known of this hybrid, P. × torssanderi, worldwide. Isozyme analysis indicated the colony to be genetically uniform. The plants studied represented a single clone that seems to have persisted at this site for a long time.
 
Kaplan Z. (2007): First record of Potamogeton × salicifolius for Italy, with isozyme evidence for plants collected in Italy and Sweden. – Pl. Biosystems 141: 344–351.
Potamogeton × salicifolius, a hybrid between P. lucens and P. perfoliatus, is identified as a new taxon for Italy. This is the first record of this hybrid from southern Europe. The Italian sample was studied in cultivation and compared with a living specimen of P. × salicifolius from Sweden, where the hybrid is rather widespread. In addition to morphological features, the most compelling evidence for the hybrid origin of these plants came from the isozyme analysis. The additive “hybrid” banding patterns of the five enzyme systems studied indicate inheritance from P. lucens and P. perfoliatus. The distribution of this hybrid in Europe coincides with the areas most severely affected by the Late Pleistocene glaciation. The relationships between environmental conditions, history of the habitat and rise of hybrids are discussed.
 
Kaplan Z. & Fehrer J. (2006): Comparison of natural and artificial hybridization in Potamogeton. – Preslia 78: 303–316.
The first attempt to artificially hybridize species of Potamogeton resulted in the hybrid P. perfoliatus × P. gramineus. The morphological features, reproductive behaviour and molecular markers of the offspring of this experimental hybridization were compared with those of the parental species and natural hybrids of the same assumed parentage. A phenotype corresponding to that of the natural hybrid P. × nitens was acquired from an experimental cross between P. perfoliatus and P. gramineus. All plants, both natural and artificial, of this hybrid were consistently sterile. They showed the ITS variants of both parental taxa, which is consistent with biparental inheritance of nuclear DNA. The experimental hybrid was used to test the maternal inheritance of chloroplast DNA in Potamogeton. Sequences of a chloroplast intergenic spacer (rpl20-rps12) were identical with those of the female parent. Then, the directions of the crosses resulting in the natural hybrids were investigated. Of five natural populations of P. × nitens, P. gramineus was the maternal parent of two and P. perfoliatus of three populations. The frequency of hybridization events and rise of hybrids are discussed.
 
Kaplan Z. (2005): Potamogeton schweinfurthii A. Benn., a new species for Europe. – Preslia 77: 419–431.
The occurrence in the Mediterranean part of Europe of the African species Potamogeton schweinfurthii is recorded for the first time. So far, this native but overlooked species has been found on five major Mediterranean islands: Corsica, Sardinia, Malta, Kefallinía (Ionian Islands, Greece) and Crete. The species is most similar and presumably closely related to the mainly Eurasian P. lucens, with which it has been partly confused. The nomenclature and a description of P. schweinfurthii are provided, and its taxonomy and how it differs from similar taxa discussed. All known localities are listed, together with voucher specimens preserved in the major European herbaria. A distribution map of P. schweinfurthii in the Mediterranean region is presented.
 
Kaplan Z. (2005): Neotypification of Potamogeton ×fluitans Roth and the distribution of this hybrid. – Taxon 54: 822–826.
The identity of the name Potamogeton fluitans Roth has for a long time been uncertain. An analysis of the history of the name and its use is presented and the identity of the extant material ascribed to Roth discussed. The name P. fluitans is neotypified with a specimen from a population of the hybrid P. lucens L. × P. natans L. recently studied morphologically, anatomically and electrophoretically. Nomenclature of the hybrid is summarized and lectotypes for a further four names designated. Distribution of the hybrid is described and a list of representative specimens given.
 
Krahulec F., Kaplan Z. & Novák J. (2005): Tragopogon porrifolius × T. pratensis: the present state of an old hybrid population in Central Bohemia, the Czech Republic. – Preslia 77: 297–306.
A population of a hybrid between Tragopogon porrifolius and T. pratensis (T. ×mirabilis), which occurs in SW part of the town of Roudnice nad Labem, N part of Central Bohemia, was analysed with respect to its morphology, fertility, life history, ploidy level and DNA content. Both parental species vary relatively little morphologically; they are biennials (monocarpic perennials) and diploids. T. pratensis is a native species in the Czech Republic, T. porrifolius was cultivated there in the past. The hybrid plants are extremely morphologically variable, with variation ranges of some characters overlapping those of the parental species (e.g. ligules are often longer than involucral bracts, peduncles are often lanate). Only diploids were found within the hybrid population; however, they have substantially lower DNA content than both parents (18% lower than T. pratensis, 42% lower than T. porrifolius). The plants of the Roudnice hybrid population are polycarpic perennials in contrast to the monocarpic perennial (mostly biennial) parents. The distribution is described in detail; it shows that the hybrid plants are spreading and at present even occur outside the town. The long-persisting population of fertile diploid hybrid plants in Roudnice nad Labem is an alternative evolutionary pathway to that of the allotetraploid Tragopogon species known from North America.
 
Kaplan Z. & Symoens J.-J. (2005): Taxonomy, distribution and nomenclature of three confused broad-leaved Potamogeton species occurring in Africa and on surrounding islands. – Bot. J. Linn. Soc. 148: 329–357.
A taxonomic revision of broad-leaved Potamogeton species ascribed to the ‘P. schweinfurthiithunbergii complex’ occurring in Africa and on surrounding islands is presented. Three species, P. nodosus, P. richardii and P. schweinfurthii, are recognized in the African mainland. The widespread species P. nodosus has been widely overlooked in sub-Saharan Africa. It is recorded here for the first time from eight countries of tropical and southern Africa and from six surrounding islands. The distribution of P. richardii is critically revised and the species is recorded for the first time from Cameroon, Swaziland and Madagascar. P. schweinfurthii is recorded for the first time from Algeria, Tunisia, Burkina Faso and Niger. The nomenclature of all three species is revised. Lectotypes are designated for six names. All original material of the name P. thunbergii Cham. et Schltdl. actually belongs to P. nodosus Poir. The correct name for the East and southern African species called ‘P. thunbergii’ is P. richardii Solms. The lectotype of P. schweinfurthii designated by Dandy proved to be P. nodosus. A new type is therefore proposed for the species generally named P. schweinfurthii and the name itself is proposed for conservation. The morphology and stem anatomy of P. nodosus, P. richardii and P. schweinfurthii are described. In spite of some overlaps in the morphological variation in their vegetative characters, a detailed analysis of the variation patterns and instructions for reliable identification are given. The distributions of all three species are described, based solely on reliably identified specimens, many of which were also examined anatomically. Distribution maps are provided.
 
Kaplan Z. & Zalewska-Gałosz J. (2004): Potamogeton taxa proposed by J. F. Wolfgang and his collaborators. – Taxon 53: 1033–1041.
In the first half of 19th century Jan Fryderyk Wolfgang (1775-1859) was the outstanding expert on Potamogetonaceae. Twelve of the names he proposed in a manuscript of a monograph on Potamogeton were validly published by Schultes & Schultes (1827). Of these, four names are now the correct names for the respective taxa, one for a species (P. rutilus Wolfg.) and three for hybrids (P. ×nerviger Wolfg., P. ×salicifolius Wolfg. and P. ×undulatus Wolfg.). Ten names of Potamogeton taxa described by Wolfgang are typified in this paper, together with two names proposed by his collaborators, Besser and Gorski. The identity of these names is discussed.
 
Kaplan Z. & Fehrer J. (2004): Evidence for the hybrid origin of Potamogeton ×cooperi (Potamogetonaceae): traditional morphology-based taxonomy and molecular techniques in concert. – Folia Geobot. 39: 431–453.
The identity of plants morphologically intermediate between Potamogeton crispus and P. perfoliatus from two recently discovered sites, one in Moravia, Czech Republic and another in Wales, United Kingdom, was investigated with molecular markers. Evidence from restriction fragment length polymorphism analysis of the nuclear internal transcribed spacer region of ribosomal DNA and of the trnK-trnQ chloroplast DNA intergenic spacer confirmed the morphology-based determination of two putative hybrid samples as P. ×cooperi. The hybrids showed the ITS variants of both parental taxa, consistent with the expected biparental inheritance of nuclear DNA. The chloroplast DNA markers indicate P. crispus as the female parent in both hybridization events. The hybrid origin of another dubious sample was excluded by the molecular data, in accordance with previous detailed morphological examination. This plant represented an extreme, narrow-leaved form of P. perfoliatus, imitating P. ×cooperi in some characters. The results of the molecular analyses are discussed in relation to the morphology of the plants. They underline that some Potamogeton hybrids could indeed be identified by careful and detailed morphological examination and also that these identifications were reliable and confirmed by molecular markers. This study exemplifies that long-term taxonomic expertise usually generates very well-founded specific questions suitable for straightforward treatment by appropriate molecular methods. The process and ecological implications of hybrid formation are also discussed.
 
Kaplan Z. & Wolff P. (2004): A morphological, anatomical and isozyme study of Potamogeton ×schreberi: confirmation of its recent occurrence in Germany and first documented record in France. – Preslia 76: 141–161.
A combined study of morphology, stem anatomy and isozyme patterns was used to reveal the identity of sterile plants from two rivers on the Germany/France border. A detailed morphological examination proved that the putative hybrid is clearly intermediate between Potamogeton natans and P. nodosus. The stem anatomy had characteristics of both species. The most compelling evidence came from the isozyme analysis. The additive “hybrid” banding patterns of the six enzyme systems studied indicate inheritance from P. natans and P. nodosus. In contrast, other morphologically similar hybrids were excluded: P. ×gessnacensis (= P. natans × P. polygonifolius) by all the enzyme systems, P. ×fluitans (= P. lucens × P. natans) by AAT, EST and 6PGDH, and P. ×sparganiifolius (= P. gramineus × P. natans) by AAT and EST. All samples of P. ×schreberi are of a single multi-enzyme phenotype, suggesting that they resulted from a single hybridization event and that the present-day distribution of P. ×schreberi along the Saarland/Moselle border was achieved by means of vegetative propagation and long-distance dispersal. Neither of its parental species occur with P. ×schreberi or are present upstream, which suggests that this hybrid has persisted vegetatively for a long time in the absence of its parents. The total distribution of this hybrid is reviewed and a detailed account of the records from Germany is given. P. ×schreberi appears to be a rare hybrid. The risk of incorrect determination resulting from the identification of insufficiently developed or inadequately preserved plant material is discussed.
 
Kaplan Z. & Štěpánek J. (2003): Genetic variation within and between populations of Potamogeton pusillus agg. – Plant Syst. Evol. 239: 95-112.
Patterns of isozyme variation were examined in 17 populations of P. pusillus and P. berchtoldii, together with 1 population of P. trichoides taken for comparison. Both P. pusillus and P. berchtoldii displayed low levels of variation within populations associated with high levels of interpopulation differentiation. This pattern of partitioning of genetic variation within and between populations is attributed to the founder effect, frequent vegetative propagation by turions, dominant self-fertilization and limited seedling recruitment. The mechanism of pollen transfer was investigated in cultivation. Effective pollination takes place in air above the water surface (autogamy, geitonogamy, anemogamy), on the water surface (epihydrogamy) or below water surface (hydroautogamy). The species are self-compatible. The low level of infra-population variation together with rare occurrence of heterozygotes suggest that selfing is the most frequent mode of pollination, although the protogynous flowers may occasionally permit some cross-pollination. Unique enzyme markers were found for P. pusillus and P. berchtoldii, and also for the single population of P. trichoides. All multienzyme phenotypes were species-specific. Isozyme data support the separate position of P. pusillus and P. berchtoldii. UPGMA dendogram based on enzyme data of 133 plant samples revealed three distinct main enzymatic entities perfectly corresponding to the three morphologically defined species.
 
Kaplan Z. (2003): Linear-leaved species of Potamogeton in the Czech Republic V. P. pectinatus. – Preslia 75: 165–181.
The last part of a revision of linear-leaved species of the genus Potamogeton in the Czech Republic focuses on P. pectinatus. This species is the only member of subgenus Coleogeton occurring in this country. Species description, relevant synonyms, illustrations, a list of specimens examined and a distribution map are provided. P. pectinatus is widespread in the Czech Republic; it is the most common Potamogeton species particularly in runningwaters. P. pectinatus still quite often grows in most lowland rivers and their basins.
 
Kirschner J. & Kaplan Z. (2002): Taxonomic monographs in relation to global Red Lists. – Taxon 51: 155–158.
Upon comparison with recent monographs of Juncaceae and Potamogetonaceae, the 1997 IUCN Red List of Threatened Plants is shown to be an inadequate information source for conservation decisions. A substantial proportion of names listed in the IUCN RL represent synonyms, often belonging to widespread taxa, or remain doubtful taxonomically. If a new Red List is derived from the two new monographic accounts, and compared with the 1997 IUCN RL, the correct data from the latter represent 10–25% of the former. It may concluded that the overall accuracy of the IUCN list is rather low. The importance of global taxonomic monographs as a source of basic data for the accurate compilation of Red Lists is stressed.
 
Kaplan Z. (2002): Linear-leaved species of Potamogeton in the Czech Republic IV. P. pusillus s.l. and P. trichoides. – Preslia 74: 345–371.
The fourth part of a revision of linear-leaved species of the genus Potamogeton in the Czech Republic is given, dealing with P. pusillus s.l. and P. trichoides. The appropriate taxonomic concept and species delimitation within P. pusillus s.l. are discussed. Because of still unresolved taxonomic difficulties and high percentage of specimens that cannot be assigned to one of the two traditionally distinguished species, P. pusillus s. str. (syn. P. panormitanus) and P. berchtoldii, the broader concept of P. pusillus s.l. has tentatively been adopted in this revision. This species complex is widespread in the Czech Republic, absent only in relatively small areas of the highest elevations and the driest areas without suitable biotopes. P. pusillus s.l. is the commonest taxon of Potamogeton in standing waters. P. trichoides, a well defined species distinguished by several morphological characters, occurs scattered mainly in S, C and E Bohemia and S and C Moravia, with most localities concentrated in S Bohemia. It is considered as strongly threatened species of the Czech flora. Species descriptions, relevant synonyms, illustrations, a list of specimens examined and distribution maps are provided for both species. P. rutilus was once reported from the Czech Republic in error. No specimen from this country has been found in herbaria.
 
Kaplan Z., Plačková I. & Štěpánek J. (2002): Potamogeton ×fluitans (P. natans × P. lucens) in the Czech Republic. II. Isozyme analysis. – Preslia 74: 187–195.
Evidence from isozyme electrophoresis confirmed previous hypothesis on the occurrence of interspecific hybridization between Potamogeton natans L. and P. lucens L. formulated on the basis of morphology and stem anatomy. Isozyme phenotypes of the morphologically intermediate plants were compared with those obtained from the putative parents growing in the same locality. P. natans and P. lucens differed consistently in at least 12 loci and possessed different alleles at 7 loci. The hybrid had no unique alleles and exhibited an additive “hybrid” isozyme pattern for all 7 loci that could be reliably analysed and where the parents displayed different enzyme patterns. Both true parental genotypes were detected among samples of plants of P. lucens and P. natans from the same locality. The hybrid plants represent a recent F1 hybrid generation resulting from a single hybridization event. Consistent differences in enzyme activity between submerged and floating leaves of P. natans and P. ×fluitans were observed in all interpretable enzyme systems.
 
Kaplan Z. (2002): Phenotypic plasticity in Potamogeton (Potamogetonaceae). – Folia Geobot. 37: 141–170.
Sources of the extensive morphological variation of the species and hybrids of Potamogeton were studied, especially from the viewpoint of the stability of the morphological characters used in Potamogeton taxonomy. Transplant experiments, the cultivation of clones under different values of environmental factors, and the cultivation of different clones under uniform conditions were performed to assess the proportion of phenotypic plasticity in the total morphological variation. Samples from 184 populations of 41 Potamogeton taxa were grown. The immense range of phenotypic plasticity, which is possible for a single clone, is documented in detail in 14 well-described examples. The differences among distinct populations of a single species observed in the field were mostly not maintained when grown together under the same environmental conditions. Clonal material cultivated under different values of environmental factors produced distinct phenotypes, and in a few cases a single genotype was able to demonstrate almost the entire range of morphological variation in an observed trait known for that species. Several characters by recent literature claimed to be suitable for distinguishing varieties or even species were proven to be dependent on environmental conditions and to be highly unreliable markers for the delimitation of taxa. The unsatisfactory taxonomy that results when such classification of phenotypes is adopted is illustrated by three examples from recent literature. Phenotypic plasticity was found to be the main source of morphological variation within the species of Potamogeton, having much more influence than morphological differences caused by different genotypes.
 
Kaplan Z. (2002): Main sources of taxonomic difficulties in Potamogeton. – Zprávy Čes. Bot. Společ. (Praha) 37: 43–46.
Main sources of taxonomic difficulties in Potamogeton are identified and described. Prevailing clonal reproduction, autogamy and the founder effect play the principal roles in genetic structure of populations. Genetic variation is higher between than within populations. Extensive phenotypic plasticity and parallel evolution giving rise to shared morphological similarities obscure relationships between evolutionary units and their morphology. Occasionally evolving hybrids are sometimes difficult to distinguish from the respective parent species and some of them may be thus overlooked. In contrast, extreme morphotypes of true species are sometimes misidentified as hybrids. Even though hybridisation does not seem to be frequent event in Potamogeton, once established hybrids can persist in their localities for a long time or even spread vegetatively.
 
Kaplan Z. (2002): Linear-leaved species of Potamogeton in the Czech Republic III. P. obtusifolius and P. friesii. – Preslia 74: 267–280.
The third part of a revision of linear-leaved species of the genus Potamogeton in the Czech Republic is given. Two species, P. obtusifolius and P. friesii, are dealt with in this contribution. Species descriptions, relevant synonyms, illustrations, a list of specimens examined and distribution maps are provided. P. obtusifolius grows almost exclusively in the Bohemian part, particularly in S and E Bohemia, whereas in Moravia it is confined to a few localities mainly in its NE part (Silesia). It is classified as a threatened species of the Czech flora. P. friesii has been collected only in a few localities in C and NE Bohemia. Last time it was seen in 1989 but has not been confirmed in the site since then; thus the species belongs among missing (and probably extinct) taxa in the Czech Republic.
 
Kaplan Z. (2001): Potamogeton ×fluitans (P. natans × P. lucens) in the Czech Republic. I. Morphology and anatomy. – Preslia 73: 333–340.
Potamogeton ×fluitans Roth (P. natans L. × P. lucens L.) was discovered in NE Bohemia as a new taxon for the Czech Republic. In the site, the hybrid grew together with both its parents. The revision of herbarium specimens proved that all previous records of “P. fluitans” from the Czech Republic were erroneous. Morphological and anatomical characters of the hybrid are described, together with those of its parents and other morphologically similar taxa. P. ×fluitans differs from P. natans especially in having submerged leaves with a distinct lamina and petioles of floating leaves without a flexible section at the junction with the lamina. From P. lucens, it is distinguished by the capability of developing floating leaves and by long, narrowly oblong submerged leaves. While stem anatomical pattern of P. ×fluitans is intermediate between those of its parents, it is easily distinguishable from that of morphologically the most similar P. nodosus Poir. The hybrid is sterile and no trace of developed fruits has been found among the Czech material.
 
Kirschner J. & Kaplan Z. (2001): Taxonomic and nomenclatural notes on Luzula and Juncus (Juncaceae). – Taxon 50: 1107–1113.
New taxa and combinations are presented to be included in the prepared treatment of Juncaceae in the Flora of the World. A new section, Luzula sect. Atlanticae, and a new species, Luzula indica, are described, and three new combinations are made: Luzula nipponica (Satake) Kirschner & Miyamoto, L. lutescens (Koidzumi) Kirschner & Miyamoto, and Luzula alpino-pilosa subsp. deflexa (Kozuharov) Kirschner. A new name, Juncus meianthus K. Wilson is proposed for a later homonym, J. gracilis R. Br. The name Luzula acuminata Raf. is neotypified in order to retain its current usage.
 
Kaplan Z. (2001): Linear-leaved species of Potamogeton in the Czech Republic: II. P. compressus and P. acutifolius. – Preslia 73: 127–139.
A revision of linear-leaved species of the genus Potamogeton in the Czech Republic is given. Two species, P. compressus and P. acutifolius, are dealt with in this paper. Species descriptions, relevant synonyms, illustrations, a list of specimens examined and distribution maps are provided. P. compressus, always an extremely rare taxon in the Czech Republic, is now extinct. P. acutifolius, now strongly endangered in its occurrence, has main centres of its distribution in pond areas in SW and E Bohemia.
 
Kubát K. & Kaplan Z. (2001): Arnoseris minima Schweigg. et Koerte in the Czech Republic. – Severočes. Přír. (Litoměřice) 32("2000"): 29–36.
Arnoseris minima is a scarce and critically endangered species of the Czech flora. Altogether, it has been found on approximately 200 localities but during the last 20 years it has been confirmed to still occur in only 12 sites. These recent localities are confined to N and S Bohemia. A list of specimens examined and a distribution map are provided.
 
Kaplan Z. (2001): Taxonomic and nomenclatural notes on Luzula subg. Pterodes (Juncaceae). – Preslia 73: 59–71.
New taxa and combinations are given resulting from a revision of Luzula subg. Pterodes (Griseb.) Buchenau for the monographic treatment of Juncaceae for Species plantarum: Flora of the world. Luzula jimboi Miyabe et Kudo subsp. atrotepala Z. Kaplan, subsp. nova, and L. plumosa E. Mey. subsp. dilatata Z. Kaplan, subsp. nova, are described. Three new combinations, L. forsteri (Sm.) DC. subsp. rhizomata (Ebinger) Z. Kaplan, comb. nova, L. acuminata Raf. subsp. carolinae (S. Watson) Z. Kaplan, comb. nova, and L. plumosa E. Mey. subsp. reflexa (Ebinger) Z. Kaplan, comb. nova, are proposed for taxa with obvious geographically correlated variations. Identity of L. cechica Domin, a name proposed for the putative hybrid of L. luzuloides × L. pilosa, and that of a misapplied name L. rostrata Buchenau is elucidated. Diagnostic characters of members of taxonomically difficult groups are given. Eight names are lectotypified.
 
Kaplan Z. (2000): Linear-leaved species of Potamogeton in the Czech Republic: I. Introduction and key to determination. – Preslia 72: 457–467.
A revision of linear-leaved species of the genus Potamogeton in the Czech Republic is given. On the basis of field investigation, cultivation experiments and herbarium studies, 8 taxa have been recognized as distinct species. Prevailing clonal reproduction, autogamy, easy dispersal on long distances, and especially extensive phenotypic plasticity are taken for the principal sources of taxonomic difficulties. Description and explanation of special morphologic terms, comments on infrageneric classification, and instructions for collecting and drying of specimens are provided. This first part of a series of papers on linear-leaved species includes also key to determination.
 
Kaplan Z. (2000): Lemna turionifera – a new species for the Czech Republic. – Zprávy Čes. Bot. Společ. (Praha) 34("1999"): 135–141.
Lemna turionifera has been found as a new species for the Czech Republic. It is only known from a single site so far: northern Bohemia, Distr. Turnov, Český ráj Landscape Area, Březina village, small concrete water reservoir in Kurovodice settlement, 0.8 km S–SSE of the Březina railway-station, 255 m a. s. l., 18 September 1997, leg. Z. Kaplan 97/908. Voucher specimens are deposited in the herbarium of the present author at the Institute of Botany, Průhonice, Czech Republic, and in the herbarium of Prof. E. Landolt at the Geobotanisches Institut ETH, Stiftung Rübel, Zürich, Switzerland, who kindly revised the determination. The aim of the present paper is to make current knowledge on the species accessible to Czech botanists in order to stimulate them to look for it in the field. Differential characters of L. turionifera are listed in the paper. A key to the determination to all Central European members of Lemnaceae together with their illustrations are provided as well.
 
Kirschner J., Novara L. J., Novikov V. S., Snogerup S. & Kaplan Z. (1999): Supraspecific division of the genus Juncus (Juncaceae). – Folia Geobot. 34: 377–390.
New classification of the genus Juncus (Juncaceae) is presented. The genus is divided in two subgenera, characterized by the presence/absence of bracteoles and the structure of inflorescence. Lower rank subdivisions, sections, generally correspond to the traditionally recognized subgenera introduced by Buchenau. A new name is introduced for what has been called subg. (sect.) Ensifolii, Juncus sect. Iridifolii. A checklist of supraspecific names in Juncus, with typification and references to the sectional names accepted, is presented in the Appendix.
 
Wiegleb G. & Kaplan Z. (1998): An account of the species of Potamogeton L. (Potamogetonaceae). – Folia Geobot. 33: 241–316.
An account of the taxonomy of the genus Potamogeton L. with special reference to species description and delimitation is presented. A key to the species is given, based as far as possible on vegetative characters. Detailed descriptions are provided for a total of 69 species which are regarded as sufficiently well known. Special emphasis is laid both on a complete list of relevant characters as well as on the judgement of their respective diagnostic values. All important synonyms are listed allowing direct access to most of the relevant taxonomic and floristic Potamogeton literature. 50 confirmed hybrids are listed and assigned to their putative parent species. Questions with respect to the taxa listed are formulated in notes on each of the species. A more general view and questions on future Potamogeton research are summarized in the conclusions.
 
Kaplan Z. & Řehořek V. (1998): Galium parisiense - a new alien species for the Czech Republic. – Preslia 70: 51–56.
Two specimens of Galium parisiense L. having their origin in the wild in the Czech Republic have been found during the study of the herbaria of PR and BRNM. The species has never been reported for the country before. The earlier collection is from the present-day area of Prague in central Bohemia, the later one from a field near the village of Nedachlebice in southeastern Moravia. Both localities are situated on the northeastern border of the species distribution. No recent occurrence of the species in the wild in the Czech Republic has been reported, except for the single find in a concrete flower-bowl in Brno, southern Moravia. Infraspecific variation and its taxonomic evaluation is discussed in the present paper.
 
Kaplan Z. (1998): Relict serpentine populations of Knautia arvensis s. l. (Dipsacaceae) in the Czech Republic and an adjacent area of Germany. – Preslia 70: 21–31.
Several distinct populations of Knautia arvensis (L.) Coulter s. l. restricted to serpentine outcrops have been found in the Czech Republic and an adjacent area of Germany. They have been determined as diploids or tetraploids despite the fact that only common, non-serpentine tetraploids occur in the area. These plants differ also in their morphology, florogenesis, and in their behaviour within a plant community from all other known taxa within the species. Their origin has been explained by the hypothesis of microevolution of a relict diploid ancestor. The isolated relict populations have not expanded their range, being confined to the place where they originated.
 
Kaplan Z. (1997): Names of Potamogeton (Potamogetonaceae) proposed by Bohemian botanists in the period 1819–1902. – Preslia 69: 193–239.
Names of taxa of the genus Potamogeton proposed by Bohemian authors are discussed and typified. 74 names are listed, proposed by L. Čelakovský, F. X. Fieber, P. M. Opiz, J. S. Presl, K. B. Presl (= C. B. Presl), J. Rohlena, F. J. Ruprecht, D. Sloboda and I. F. Tausch. Three names and their types are of importance for contemporary plant taxonomy: P. berchtoldii Fieber, P. ×angustifolius J. S. Presl [= P. gramineus L. × P. lucens L.] and P. friesii Rupr. The study has also proved the justification of the use of these names. The correct name for the species known as P. malaianus [auct.] or P. mucronatus C. B. Presl is P. wrightii Morong. In order to preserve nomenclatural stability, a justification for the conservation of the name P. maackianus A. Benn. against P. serrulatus Regel et Maack is given.
 
Krahulec F. & Kaplan Z. (1995): Diversity of Potamogeton species during 21 years of succession in a new water reservoir. – Preslia 66: 237–241.
The composition of the Potamogeton flora and its changes during 21 years of vegetation succession in the new water reservoir Rozkoš in East Bohemia are described. Ten species and two hybrids were observed at this locality during this period and in two years preceding the flooding. It seems highly probable that this richness was confined only to a short period during the succession. Diversity was correlated with trophic conditions in the reservoir.
 
Kaplan Z. (1995): Genus Potamogeton on the Svjatoj Nos isthmus and in the Barguzinskaja valley, Lake Baikal. – Siber. Nat. (Praha) 1: 73–89.
Genus Potamogeton was studied in two wetlands in the eastern vicinity of Lake Baikal: on the isthmus of the Svjatoj Nos Peninsula with adjacent parts of Čivyrkujskij Bay and in Barguzinskaja Basin. Distribution of Potamogeton taxa is presented, based on the authors fieldwork and published data. Taxonomical, ecological and syntaxonomical comments are also given. The possibility of the occurrence of Potamogeton taxa recently described from Siberia is discussed.