Recurrent polyploid formation and weak reproductive barriers between independent polyploid lineages generate intricate species complexes with high diversity and reticulate evolutionary history. Uncovering the evolutionary processes that formed their present-day cytotypic and genetic structure is a challenging task. We studied the species complex of Cardamine pratensis, composed of diploid endemics in the European Mediterranean and diploid-polyploid lineages more widely distributed across Europe, focusing on the poorly understood variation in Central Europe. To elucidate the evolution of Central European populations we analyzed ploidy level and genome size variation, genetic patterns inferred from microsatellite markers and target enrichment of low-copy nuclear genes (Hyb-Seq), and environmental niche differentiation. We observed almost continuous variation in chromosome numbers and genome size in C. pratensis s.str., which is caused by the co-occurrence of euploid and dysploid cytotypes, along with aneuploids, and is likely accompanied by inter-cytotype mating. We inferred that the polyploid cytotypes of C. pratensis s.str. are both of single and multiple, spatially and temporally recurrent origins. The tetraploid Cardamine majovskyi evolved at least twice in different regions by autopolyploidy from diploid Cardamine matthioli. The extensive genome size and genetic variation of Cardamine rivularis reflects differentiation induced by the geographic isolation of disjunct populations, establishment of triploids of different origins, and hybridization with sympatric C. matthioli. Geographically structured genetic lineages identified in the species under study, which are also ecologically divergent, are interpreted as descendants from different source populations in multiple glacial refugia. The postglacial range expansion was accompanied by substantial genetic admixture between the lineages of C. pratensis s.str., which is reflected by diffuse borders in their contact zones. In conclusion, we identified an interplay of diverse processes that have driven the evolution of the species studied, including allopatric and ecological divergence, hybridization, multiple polyploid origins, and genetic reshuffling caused by Pleistocene climate-induced range dynamics.
Solidago ×niederederi Khek (1905: 22) is a hybrid between North-American S. canadensis Linnaeus (1753: 878) and European native S. virgaurea Linnaeus (1753: 880). Solidago canadensis was introduced to Europe in the 17th century (Kowarik 2003). It has spread invasively throughout Europe since the second half of the 19th century (Weber 1998), reaching, besides sites disturbed by human activity, also (semi)natural biotopes, as forest edges, abandoned meadows and field margins which are often inhabited by native S. virgaurea. Their hybrid was discovered for the first time in nature by a local schoolmaster Franz Niedereder in the area of Vorderstoder village (Austria). Niedereder sent a plant material of the assumed hybrid to Eugen Johan Khek (born in 1861, Neuhaus/Jindřichov Hradec; died in 1927, Vienna), the pharmacist and botanist who lived in Vienna since 1889 (Anonymous 1916). Khek described the hybrid species under the name S. ×niederederi in honour of his discoverer (Khek 1905). The protologue indicates that the relevant communication between Niedereder and Khek was going on between July 1900 (when they met for the first time) and February 1905 (when the hybrid’s description was published). Before its description, Khek studied the hybrid for four years and he saw a herbarium material from Niedereder as well as a living material. In the protologue, no particular herbarium specimens or illustrations had been indicated or associated with S. ×niederederi (Khek 1905).
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