Phylogeny and classification of the Australasian and Indomalayan mimosoid legumes Archidendron and Archidendropsis (Leguminosae, subfamily Caesalpinioideae, mimosoid clade)

Abstract

The morphologically variable genus Archidendron is the second largest mimosoid legume genus from the Indomalayan-Australasian region, yet it has not been well represented in phylogenetic studies. Phylogenies that have included multiple representatives of Archidendron suggest it may not be monophyletic, and the same applies to Archidendropsis, another understudied genus of the Archidendron clade. The most comprehensive phylogeny of Archidendron and Archidendropsis to date is presented, based on four nuclear markers (ITS, ETS, SHMT and RBPCO). Exemplars from all genera of the wider Archidendron clade are sampled, including representatives of all series within Archidendron and the two subgenera of Archidendropsis. Our results confirm that Archidendron and Archidendropsis are not monophyletic. Within Archidendron, only one series (ser. Ptenopae) is resolved as monophyletic and species of Archidendron are divided into two primarily geographic lineages. One clade is distributed in western Malesia and mainland Asia and includes most representatives of series Clypeariae, while the other is mostly restricted to eastern Malesia and Australia and includes representatives of the seven other series plus two samples of series Clypeariae. No taxonomic changes are made for Archidendron due to the high level of topological uncertainty and the lack of discrete macromorphological characters separating these two lineages. Each of the two subgenera of Archidendropsis is monophyletic but they are not closely related. A new genus endemic to Queensland (Australia), Heliodendron Gill.K. Br. & Bayly, gen. nov., is described for the former Archidendropsis subg. Basaltica, and combinations for its three species are proposed: Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly, comb. nov., Heliodendron thozetianum (F. Muell.) Gill.K. Br. & Bayly, comb. nov., and Heliodendron xanthoxylon (C.T. White & W.D. Francis) Gill.K. Br. & Bayly, comb. nov.