A review of rhynchosia section polytropia (Phaseoleae, Fabaceae) and a new species from the Western Cape Province, South Africa

Rhynchosia sect. Polytropia is restricted to South Africa and comprises two closely related species (R. ferulaefolia and R. pinnata), which are characterized by pinnately or bipinnately plurijugate, or decompound leaves. The identity of the latter species is, however, uncertain. Several specimens, mostly from the Caledon and neighbouring areas in the Western Cape Province of South Africa, were erroneously assigned to R. pinnata. These specimens belong to a hitherto undescribed species, here named Rhynchosia smithiana. Although this species lacks the distinctive compound leaves typical of section Polytropia, it resembles R. pinnata and R. ferulaefolia in having a spreading, non-twining habit and congested multi-flowered inflorescences. Diagnostic features of the constituent species of section Polytropia, including the newly described species, are reported. A key to the species of this group is also presented, as well as morphological illustrations and distribution maps.