Molecular phylogenetics of Thymelaeaceae-Thymelaeoideae: resolving the paraphyly of Gnidia and a new monophyletic generic classification for the group

Abstract

Earlier phylogenetic analyses of the family Thymelaeaceae using combined plastid (matK, rbcL, rps16, trnL-F) and nuclear (ITS) regions showed that the African-Malagasy genus Gnidia was extensively polyphyletic in relation to the southern African genera Lachnaea, Passerina and Struthiola, as well as to other Southern Hemisphere genera such as Drapetes, Kelleria and Pimelea. We present here a robust and well-sampled phylogenetic analysis of the subfamily Thymelaeoideae, with sampling in Gnidia increased to 76% of the species, to better resolve the polyphyly of the genus. Our analysis retrieved seven lineages of Gnidia nested in four independent evolutionary clades within the “Gnidia group” of the subfamily Thymelaeoideae. We analysed the options available for re-circumscribing Gnidia as a monophyletic genus, with secondary considerations of nomenclatural stability, phylogenetic and biogeographic information, and ease of identification. The option that we present retains the traditionally recognized genera Drapetes, Kelleria, Lachnaea, Passerina, Pimelea and Struthiola through the recognition of six lineages of Gnidia at the generic level. We propose that Gnidia be retained as a monotypic genus, including only the type of the genus name G. pinifolia. We reinstate the four previously recognized genera Basutica, Craspedostoma, Gnidiopsis and Thymelina and recognize the two new genera Epichroxantha and Phidia for the remaining two lineages of continental African Gnidia for which no names were available, plus the monotypic Zacharia for an anomalous Malagasy species that was previously excluded from Lasiosiphon. A taxonomic key and descriptions are provided for the genera in the “Gnidia group”. We also provide the necessary new combinations for names of Gnidia species now transferred to other genera.