Globally grown, but poorly known: species limits and biogeography of Gazania Gaertn. (Asteraceae) inferred from chloroplast and nuclear DNA sequence data

Abstract

Gazania is a popular horticultural subject worldwide and comprises 16 species, all from southern Africa. However, species delimitation is difficult as many species are morphologically variable. Here we present a phylogenetic analysis of 15 species of Gazania, based on DNA sequence data from four non-coding chloroplast regions (trnL-intron, trnL-trnF spacer, psbA-trnH spacer, rps16 intron) and two nuclear spacers (InternalTranscribed Spacer, ITS; partial External Transcribed Spacer, ETS). The phylogenies derived from the plastid and nuclear datasets were not entirely congruent, but data combination was undertaken. Of the 15 species sampled, only 7 are supported as monophyletic. Most of the remaining taxa form a large, poorly resolved clade corresponding to a large, morphologically variable species complex. Using a range of ITS mutation rates, the diversification of the genus is estimated to have begun approximately 6.6 mya. The phylogeny, in conjunction with the distribution patterns, suggests that this genus arose in the semi-arid to arid Richtersveld/Namib regions of South Africa and Namibia.