Cardamine occulta, the correct species name for invasive Asian plants previously classified as C. flexuosa, and its occurrence in Europe

The nomenclature of Eastern Asian populations traditionally assigned to Cardamine flexuosa has remained unresolved since 2006, when they were found to be distinct from the European species C. flexuosa. Apart from the informal designation “Asian C. flexuosa”, this taxon has also been reported under the names C. flexuosa subsp. debilis or C. hamiltonii. Here we determine its correct species name to be C. occulta and present a nomenclatural survey of all relevant species names. A lectotype and epitype for C. occulta and a neotype for the illegitimate name C. debilis (replaced by C. flexuosa subsp. debilis and C. hamiltonii) are designated here. Cardamine occulta is a polyploid weed that most likely originated in Eastern Asia, but it has also been introduced to other continents, including Europe. Here data is presented on the first records of this invasive species in European countries. The first known record for Europe was made in Spain in 1993, and since then its occurrence has been reported from a number of European countries and regions as growing in irrigated anthropogenic habitats, such as paddy fields or flower beds, and exceptionally also in natural communities such as lake shores

Multiple hybridization events in Cardamine (Brassicaceae) during the last 150 years: revisiting a textbook example of neoallopolyploidy

Background and Aims Recently formed allopolyploid species represent excellent subjects for exploring early stages of polyploid evolution. The hexaploid Cardamine schulzii was regarded as one of the few nascent allopolyploid species formed within the past ∼150 years that presumably arose by autopolyploidization of a triploid hybrid, C. × insueta; however, the most recent investigations have shown that it is a trigenomic hybrid. The aims of this study were to explore the efficiency of progenitor-specific microsatellite markers in detecting the hybrid origins and genome composition of these two allopolyploids, to estimate the frequency of polyploid formation events, and to outline their evolutionary potential for long-term persistence and speciation. Methods Flow-cytometric ploidy-level screening and genotyping by progenitor-specific microsatellite markers (20 microsatellite loci) were carried out on samples focused on hybridizing populations at Urnerboden, Switzerland, but also including comparative material of the parental species from other sites in the Alps and more distant areas. Key Results It was confirmed that hybridization between the diploids C. amara and C. rivularis auct. gave rise to triploid C. × insueta, and it is inferred that this has occurred repeatedly. Evidence is provided that C. schulzii comprises three parental genomes and supports its origin from hybridization events between C. × insueta and the locally co-occurring hypotetraploid C. pratensis, leading to two cytotypes of C. schulzii: hypopentaploid and hypohexaploid. Each cytotype of C. schulzii is genetically uniform, suggesting their single origins. Conclusions Persistence of C. schulzii has presumably been achieved only by perennial growth and clonal reproduction. This contrasts with C. × insueta, in which multiple origins and occasional sexual reproduction have generated sufficient genetic variation for long-term survival and evolutionary success. This study illustrates a complex case of recurrent hybridization and polyploidization events, and highlights the role of triploids that promoted the origin of trigenomic hybrid

Taxonomy and evolutionary history of Alyssum montanum (Brassicaceae) and related taxa in southwestern Europe and Morocco: Diversification driven by polyploidy, geographic and ecological isolation

The Alyssum montanum–A. repens polyploid complex is a group of related perennial taxa with a diversity centre in the European (Sub)Mediterranean, controversial taxonomic treatments, and a poorly known evolutionary history. In the present study, morphological, ploidy level and genetic (AFLPs and chloroplast DNA sequences) data were collected to address the taxonomy and evolution of a sublineage of this complex distributed in southwestern Europe and Morocco. As a result, a new taxonomic treatment, differing substantially from recent concepts, is presented, including an identification key, synonymy and typifications. The recognition of several previously described but recently not accepted endemics is favoured (A. flexicaule, A. orophilum, A. rhodanense), whereas the existence of southern Iberian endemics is not supported. Most of the Iberian Peninsula is occupied by a single species for which the name A. fastigiatum is applicable. Populations from the summit areas of the Pyrenees represent a separate species, which is described here as A. cacuminum. Populations from coastal sand dunes in the Basque country (Bay of Biscay) and Galicia, recently recognised as two subspecies of A. loiseleurii, are elevated to species rank according to their genetic and morphological divergence. Alyssum atlanticum is resolved as a species confined to northern Africa and not reaching southern Spain. The distribution of A. montanum in a strict sense is much more restricted than previously reported, being delimited by the Pyrenees in the south, and the Alps in the northeast. The species complex studied here is composed of several polyploid stenoendemics confined to different mountain ranges or specific lowland habitats, and a few relatively widely distributed species. We infer that hybridisation and polyploidisation events, along with ecological and geographic isolation, have stimulated speciation in this complex. Hypotheses about the origin and evolutionary history of the species are discussed.Studies of the herbarium specimens in MA were supported by the EU FP7 SYNTHESYS project (fellowships no. ES-TAF-3099 to K.M., ES-TAF-3213 to J.Z.-L. and ES-TAF-3216 to S.Š.).Peer reviewe

Polyploidy and hybridization in the Mediterranean and neighbouring northern areas: examples from the genus Cardamine (Brassicaceae)

Summary. The genus Cardamine is distributed worldwide and is rich in polyploids. Here we review the considerable amount of knowledge accumulated on polyploid species and related diploids over the last twenty years, particularly in the Mediterranean area and neighbouring regions of Central Europe. These studies addressed the taxonomic treatment of polyploids, their origin and evolution, phylogenetic relationships to diploid and other polyploid relatives, and overall morphological, genetic, karyological and ecological patterns. The revealed parentage of polyploids such as C. asarifolia, C. flexuosa and C. ×schulzii shows the power of recently developed molecular and cytogenetic approaches, which enable us to understand how the polyploid taxa originated, became established and further evolved. It is emphasised that diploid-polyploid species complexes, such as the C. amara and C. pratensis groups, represent true natural laboratories for polyploid studies. Particularly the species complex of C. pratensis contains numerous diploid lineages and polyploid populations of all levels up to dodecaploids, including aneuploids and dysploids, providing excellent possibilities for the application of a wide spectrum of methodical approaches to understand the processes underlying polyploid evolution. Hybridization revealed in this genus occurs both at the homoploid and heteroploid levels and mainly in mountain regions, where parapatric and/or ecologically differentiated close relatives come into contact. These studies document that interspecific gene flow can result in various patterns, such as continuous variation in hybrid swarms (C. pratensis × C. raphanifolia), established hybrid species of significant evolutionary potential (C. ×schulzii, C. ×insueta), or largely sterile hybrids of first generations only and persistence through vegetative propagation (C. ×ferrarii, C. ×enriquei). All of these cases also show how recent hybridization and introgression add to the complexity of reticulated patterns of evolution in Cardamine in the Mediterranean and adjacent areas

Out of the Balkans and Anatolia to the Western Alps? Surprising phylogenetic implications for two endemic <i>Alyssum </i>(Brassicaceae) species: <i>A. cognense</i> sp. nov. and <i>A. rossetii</i>

The European Alps show a high degree of endemism associated mainly with the location of glacial refugia and environmental heterogeneity. Several Alpine endemics have evolved in the genus Alyssum. Here we study perennial Alyssum populations in the Western Alps, mainly distributed in the Aosta Valley region, which hosts high species diversity, although endemics are rare. We addressed the recently described stenoendemic A. rossetii and taxonomically uncertain populations usually attributed to A. montanum s.s. to clarify their phylogenetic position and morphological differentiation. The latter entity has been shown to be distinct from A. montanum s.s. and is described as a new species, Alyssum cognense, phylogenetically placed in the A. montanum–A. repens species complex. Both morphological and genetic patterns revealed that its closest relative occurs in the central Balkans. We present detailed ecological characteristics and morphological differentiation of A. cognense sp. nov. from its relatives and geographically closest species and speculate on its biogeographic origin. Genetic patterns (reduced diversity and nestedness) suggest long-distance dispersal from the central Balkan Peninsula. The second studied species, A. rossetii, is phylogenetically distant and belongs to the mainly Asian Alyssum section Gamosepalum lineage, which includes few representatives in southern and eastern Europe. The phylogenetically closest species of A. rossetii are Anatolian endemics, so this extreme disjunction remains puzzling. The present study illustrates the need for in-depth taxonomic and phylogenetic studies, even in well-explored Alpine regions, and also shows that the processes underlying the evolution of endemics can be complex and poorly understood.</p

Multiple hybridization events in Cardamine (Brassicaceae) during the last 150 years: revisiting a textbook example of neoallopolyploidy

Background and Aims: Recently formed allopolyploid species represent excellent subjects for exploring early stages of polyploid evolution. The hexaploid Cardamine schulzii was regarded as one of the few nascent allopolyploid species formed within the past ∼150 years that presumably arose by autopolyploidization of a triploid hybrid, C. × insueta; however, the most recent investigations have shown that it is a trigenomic hybrid. The aims of this study were to explore the efficiency of progenitor-specific microsatellite markers in detecting the hybrid origins and genome composition of these two allopolyploids, to estimate the frequency of polyploid formation events, and to outline their evolutionary potential for long-term persistence and speciation. Methods: Flow-cytometric ploidy-level screening and genotyping by progenitor-specific microsatellite markers (20 microsatellite loci) were carried out on samples focused on hybridizing populations at Urnerboden, Switzerland, but also including comparative material of the parental species from other sites in the Alps and more distant areas. Key Results: It was confirmed that hybridization between the diploids C. amara and C. rivularis auct. gave rise to triploid C. × insueta, and it is inferred that this has occurred repeatedly. Evidence is provided that C. schulzii comprises three parental genomes and supports its origin from hybridization events between C. × insueta and the locally co-occurring hypotetraploid C. pratensis, leading to two cytotypes of C. schulzii: hypopentaploid and hypohexaploid. Each cytotype of C. schulzii is genetically uniform, suggesting their single origins. Conclusions: Persistence of C. schulzii has presumably been achieved only by perennial growth and clonal reproduction. This contrasts with C. × insueta, in which multiple origins and occasional sexual reproduction have generated sufficient genetic variation for long-term survival and evolutionary success. This study illustrates a complex case of recurrent hybridization and polyploidization events, and highlights the role of triploids that promoted the origin of trigenomic hybrids