Phytogeographic study of the Kaokoveld Centre of Endemism

[摘要] An intriguing biogeographic area that lies in northwestern Namibia and southwest Angola is knownfor having numerous endemic taxa. It had, however remained vaguely defined because of thecomplex flora, the arid environment and confusing and inconsistent use of biogeographicterminology. This thesis redefined the area as a centre of endemism based on recurrent patterns ofplant distributions by shared species. The end result is a well-defined entity with regard to, not onlygeographic boundaries and floristic elements, but also to its history and floristic relationships.A vast amount of information on the plants of the area, their affinities and their distributions isrequired for a study of this nature and this was undertaken through literature surveys and field work.All the relevant information on Namibia and the southwestern Angolan flora, i.e. the region and thestudy area, were incorporated into a database which formed the bases for numerical analysis andGIS studies. The database also brought together a wide range of information from literature sourcesthat included facts and theories about the past and present physical environment. The structure ofthe database permitted querying this electronic data in many different ways.To accommodate the wide variety of subjects in a logical way, the thesis was divided into twosections. Section A concentrated on the region and provided background information and context.The theory, terminology and phytogeographic studies in the region were evaluated as a first step. Alarge amount and variety of palaeo-environmental and palaeo-ecological information, pertinent tothe region was incorporated. Secondly the flora was assessed. Besides the diversity, distributionpatterns of the plants within and outside the region, including disjunct distributions, phylogenieswere assessment. Finally taxa with similar geographic ranges were grouped. These entities weremapped and both the taxa and their environments were evaluatedSection B focused on the core area, namely the Kaokoveld Centre of Endemism, which wasdelimited by numerical techniques, and then investigated further with regard to its floristiccomponents, relationships and origins. The flora and endemic components are described in detail.The result is a well-defined centre of endemism which comprises one endemic family, 10 endemicgenera and nearly 300 endemic species. The flora of the Centre includes about 1600 species innearly 550 genera in 130 families. Three floristic Groups, identified in section A, that have aremarkable number of endemics are found in the Centre. Historical explanations for the distributionpatterns were suggested and the Group that includes Welwitschia mirabilis Hook.f., has been shownto be linked to the Arid Corridor. The demand for accurate knowledge about biodiversity has been highlighted by the Convention ofBiological Diversity and there are a remarkable number of users with different requirements today.This study provides a much needed alternate look at the plants of the region, as well as a summationof the principle phytogeographic elements of the Namibian flora. It also includes a newphytogeographic classification and map of the floristic Groups of Namibia, which will contribute todefining floristic areas in the region.

[发布机构] Stellenbosch University