Geographical affinities of the Cape flora, South Africa

ABSTRACT

Aim The flora characteristic of the Cape Floristic Region (CFR) is dominated by a relatively small number of clades that have been proposed as 'Cape clades'. These clades have variously been suggested to have African or Austral affinities. Here we evaluate the support for these conflicting hypotheses. In addition, we test the hypothesis that these clades share a common time of differentiation from their geographical neighbours.

Location The Cape Floristic Region, South Africa

Methods We use both published and unpublished phylogenetic information to investigate the geographical sister areas of the Cape clades as well as the timing and the direction of biogeographical disjunctions.

Results Almost half of the Cape clades for which unambiguous sister areas could be established show a trans-Indian Ocean disjunction. The earliest trans-Indian Ocean disjunction dates from 80 Ma. Other disjunctions date from various times in the Cenozoic, and we suggest that the process of recruiting lineages into the Cape flora might be ongoing. Relatively few Cape clades show a sister relationship with South America and tropical Africa, despite their relative geographical proximity. Numerous Cape clades contain species also found on tropical African mountains; in all cases tested, these species are shown to be embedded within the Cape clades. While many Cape clades show a relationship with the Eurasian temperate flora, this is complicated by their presence in tropical Africa. The single case study addressing this to date suggests that the Cape clade is nested within a European grade.

Main conclusions Although many Cape clades show Austral rather than African relationships, there are numerous other patterns suggestive of a cosmopolitan flora. This spatial variation is echoed in the temporal data, from which, although there is wide variance around the dates of disjunctions, it is clear the Cape flora has been assembled over a long time period. There is no simple hypothesis that can account for the geographical sources of the currently distinctive Cape flora. The phylogenetic positions of Afromontane members of Cape clades suggest a history of dispersal from the CFR, rather than the reverse.