Atlas Florae Europaeae notes, 33. Taxonomic synopsis of East European species of the Cytisusratisbonensis group (Fabaceae).

A group of species of Cytisussect.Tubocytisus with strictly lateral inflorescences, commonly referred to as C.ratisbonensis s.l., is critically revised in Eastern Europe on the basis of morphology and comprehensive treatment of herbarium specimens and observations. Seven species and two presumed hybrids are recognised. Complete accounts are provided for each species, with synonyms, typifications, brief morphological descriptions, data on ecology and distributions, taxonomic and nomenclatural annotations. Cytisuspolonicus is described as new to science, separated from C.ratisbonensis on the basis of morphology and diploid (vs. tetraploid) chromosome count. The lectotype of C.elongatus is superseded and a new lectotype is designated; this name has priority for the species previously known as C.triflorus. Six species names are newly placed to the synonymy: Chamaecytisuspineticola under Cytisusruthenicus s. str., and Cytisusczerniaevii, C.leucotrichus, C.lindemannii, C.ponomarjovii and Chamaecytisuskorabensis under Cytisuselongatus. The presumed hybrid between C.ruthenicus and C.elongatus, which was incorrectly known as C.czerniaevii, is described here as C.semerenkoanus. Cytisuslithuanicus, which has been an obscure name since its original publication, is resurrected for a newly-recognised octoploid species, which is endemic to eastern Poland, western Belarus and north-western Ukraine. The name C.cinereus is re-instated for the species previously known as C.paczoskii, and C.horniflorus is added to its synonymy; its complete distribution area is circumscribed, and its occurrence in Austria, Poland, Romania, Serbia and Slovakia is documented. Cytisuskreczetoviczii and C.elongatus are reported for the first time from Belarus, and the latter species also from Bosnia and Herzegovina, Montenegro and Slovenia. Cytisusborysthenicus and C.elongatus are reported as new to some territories in European Russia. Cytisusratisbonensis s. str. is treated as absent from Eastern Europe. The neglected protologue of C.ruthenicus is discovered, and the nomenclature of all other names is verified and corrected when necessary. The original material of C.borysthenicus is re-discovered. Five further lectotypes and one neotype are designated. Distribution areas are circumscribed on the basis of numerous herbarium collections and documented observations, identified or verified by the authors. Chromosome counts published for nameless taxa from Belarus, Ukraine and Russia are assigned to the species according to their herbarium vouchers: C.borysthenicus, C.kreczetoviczii and C.lithuanicus are octoploid (2n = 100), C.ruthenicus is tetraploid (2n = 50) and octoploid (2n = 100), and C.semerenkoanus and C.elongatus are tetraploid (2n = 50).