Karyological variation in the genus Rubus, subgenus Rubus: new data from the Czech Republic and synthesis of the current knowledge of European species.

The polyploid agamic complex in the subgenus Rubus is one of the most intricate groups in the European flora. Sources of taxonomic complexity are polyploidy, facultative apomixis, both past and recent hybridization followed by segregation, and ecological plasticity. We present an updated overview of ploidy level/chromosome number in 228 representatives of the subgenus, which are native in Europe and for which there are karyological studies. The first section is focused on new data obtained in the Czech Republic during the last 14 years. These chromosome counts and determinations of ploidy level using flow cytometry mainly concern the 19 species recently described from Europe and 14 earlier described species that were newly recorded in the Czech Republic. The first karyological findings are presented for 27 species, comprising triploids (2n = 21, eight species), tetraploids (2n = 28, seventeen species), pentaploids (2n = 35, one species) and hexaploids (2n = 42, one species). Rubus sendtneri Progel is the first hexaploid species to be recorded in the Czech Republic. Currently known karyological characters of native European species are presented and discussed in the second section. This overview involves data adopted from the recently published Atlas Florae Europaeae, to which the new data we present in the first section was added. Ploidy level is known only for 30% of more than 750 species recognized in Europe. Tetraploids make up 80% of the karyologically examined species. Only three sexual diploid species are native to Europe. Triploids are mainly in the series Discolores and Rubus of the section Rubus, while they are unknown in the evolutionary derived section Corylifolii. Pentaploid species are rather less frequent in the subgenus Rubus, but occur more often in the section Corylifolii than in the section Rubus. The rare hexaploids occur only in the section Corylifolii. Several cytotypes within one species is rare in European brambles. Members of the section Corylifolii are considered to be hybrids and segregation products, which resulted from crosses between species of the section Rubus and tetraploid R. caesius of section Caesii. In this case the pattern in the variation in the ploidy level suggests that unreduced gametes had a role in genesis of the section Corylifolii. Taxonomy in Rubus is almost exclusively based on morphological characters of the respective taxa. An actualized karyological overview may increase our understanding of the processes that shaped the present structure of this polyploid complex, namely the origin of the recent hybrids and genesis of some of the apomictic species.