Intergeneric relationships in the Gorteria clade of Arctotideae-Gorteriinae (Asteraceae), with description of a new genus, Roessleria

Previous phylogenetic studies in the Arctotideae-Gorteriinae (Asteraceae) have found support for a Gorteria clade. The results also indicated Hirpicium to be paraphyletic, whereas Gorteria and Gazania were found to be monophyletic. Previous investigations at the genus level on this group have focused only on relationships in Gazania and Gorteria, respectively, with only a few Hirpicium species included. In the present study we include more taxa than in any previous investigation, including all species of Hirpicium, all species of Gorteria and almost all taxa of Gazania. Phylogenetic analyses, based on DNA sequence data from non-coding (rps16, trnL-trnF, and psbA-trnH) as well as coding (ndhF) regions from the plastid genome resolved three major clades, but DNA sequence data from the ribosomal regions (ETS and ITS) from the nuclear genome did not support two of the three clades. The genus Hirpicium, as presently circumscribed, was paraphyletic with one group of four species nested within Gorteria and all remaining species of Hirpicium formed a monophyletic group with two clades, morphologically well-defined. As the name Hirpicium is a synonym of Gorteria, new names for the remaining Hirpicium species are proposed. For one of the Hirpicium clades, comprising Hirpicium echinus, we resurrect the genus Berkheyopsis O. Hoffm., and for the five species belonging to the second clade a new generic name, Roessleria Stångb. & Anderb., is proposed. The necessary new combinations, 12 in total, are made, as well as four lectotypifications and one neotypification. A key to the newly circumscribed genera is presented.