Sorbus omissa, a new endemic hybridogenous species from the lower Vltava river valley

Sorbus omissa is described as a new hybridogenous triploid (2n = 3x = 51) species belonging to the Sorbus latifolia group. This species is considered to be of hybrid origin, with S. danubialis and S. torminalis being its putative parental species. It is a stenoendemic whitebeam occurring in central Bohemia (Czech Republic) in the vicinity of the towns of Roztoky and Libcice nad Vltavou (Prahazapad district) in the valley of the lower Vltava river, where it grows primarily in oak forests (Viscario-Quercetum). The only two known populations contain approximately 150 individuals. This species differs from other similar Czech species of the S. latifolia group in having broadly elliptical to rhomboidal leaves with very shallowly lobed laminas, predominantly with 9-11 lateral leaf veins on each side, and is orange to orange-red fruit at maturity. Observation, morphological comparison and karyological (chromosome counts, DAPI flow cytometry) methods were used to identify this new species. A character-comparison table and a determination key including all taxa of the S. latifolia agg. endemic in the Czech Republic are provided. An illustration, a photograph and a distribution map of this new species are also presented.