A taxonomic revision of the genus Elephantorrhiza Benth (Leguminosae : Mimosoideae)

Abstract

Elephantorrhiza Benth. is a genus with eight species occurring in southern Africa. A taxonomic revision of this relatively poorly known mimosoid legume genus of medium-sized to small trees or shrubs and geoxylic suffrutices, is presented. Elephantorrhiza (family Leguminosae, subfamily Mimosoideae) is endemic to Africa, south of the equator, occurring in grassland and savanna with the highest species diversity in the central to eastern region of South Africa. Hitherto, the species delimitation and relationship among the taxa have been unsatisfactory. In Ross’ 1974 revision of the genus (Bothalia 11) and subsequent treatment of the genus in Flora of southern Africa (volume 19, part 1) nine species as well as four varieties and two subspecies were recognised. At the time it was emphasised that the Flora treatment was incomplete as several poorly known and possibly new species existed. These included at least one insufficiently known species as well as a list of serious deficiencies in the knowledge of the genus and concerns about the conservation status of E. obliqua, E. woodii, E. schinziana and E. rangei. In the present study, macromorphological (including vegetative and reproductive), anatomical and micromorphological data were used to resolve the infrageneric classification of Elephantorrhiza. It is proposed that Elephantorrhiza comprises eight species with no infraspecific taxa. The species recognised are E. burkei, E. elephantina, E. goetzei, E. obliqua, E. praetermissa, E. schinziana, E. suffruticosa and E. woodii. Keys to species, nomenclature, descriptions and geographical distribution for each of the taxa are presented. The scope of this study did not permit detailed investigation into chemical or molecular evidence. However, accounts of such aspects of the genus based on published reports are described. An in-depth study of the characters and character states as well as their variation has resulted in a better understanding of the infrageneric taxonomy of the genus. The main output of this study is the taxonomic treatment that enables users to determine correct names of Elephantorrhiza species, detailed descriptions and their distribution in the Flora of southern Africa region.