Taxonomic status of some geofrutex members of Vanguerieae (Rubiaceae): notes on Eriosemopsis and Pygmaeothamnus and the description of a new genus Bridsonia

摘要

The taxonomic status and phylogenetic position of three pyrogenic geofrutex members of Rubiaceae confined to grassland or savannah in central and southern Africa are clarified. Eriosemopsis, represented by E. subanisophylla, is a monotypic genus endemic to South Africa. Although morphologically clearly a member of tribe Vanguerieae (Rubiaceae), its exact phylogenetic placement was hitherto unknown. Using five molecular markers, we confirmed the separate generic status of Eriosemopsis and demonstrated that it is part of the Canthium group, closely related to Pygmaeothamnus chamaedendrum. This last species is shown not to be closely related to Pygmaeothamnus zeyheri, the type species of Pygmaeothamnus, and is therefore transferred to a new monotypic genus, namely Bridsonia. Recognition of Bridsonia chamaedendrum also renders Pygmaeothamnus monotypic. Illustrations of all three species involved and a distribution map for B. chamaedendrum are provided.