Phylogeny of the Neotropical element of the Randia clade (Gardenieae, Rubiaceae, Gentianales)

Abstract

Background and aims – Generic limits of the tropical tribe Gardenieae (Ixoroideae, Rubiaceae) have partly remained unsettled. We produced a new phylogeny of the Randia clade, with emphasis on its Neotropical clade comprising five genera (Casasia, Randia, Rosenbergiodendron, Sphinctanthus, and Tocoyena). The result was subsequently used to evaluate and discuss: a) the respective monophyly of the above-mentioned genera and their interrelationships; b) relationships within Tocoyena and the evolutionary relevance of its subgeneric classification; and c) the monophyly of the morphologically variable T. formosa.Material and methods – We examined the phylogeny of the Randia clade based on maximum likelihood and Bayesian analyses of sequence data from two nuclear (ETS and Xdh) and two plastid (petB-petD and trnT-F) DNA regions from 59 individuals (including seven representatives from the remaining Ixoroideae).Key results – The Neotropical clade of the Randia clade comprises three major lineages, the Randia armata subclade, the Randia-Casasia subclade and the Rosenbergiodendron subclade. Neither Casasia nor Randia is monophyletic. Tocoyena is sister to Rosenbergiodendron + Sphinctanthus and is subdivided into three lineages: the Tocoyena pittieri group, the Tocoyena guianensis group, and the core Tocoyena. Tocoyena williamsii is paraphyletic with respect to T. pittieri. Tocoyena formosa is polyphyletic and should be re-circumscribed.Conclusions – Our results demonstrate the monophyly of each of the relatively species-poor genera Rosenbergiodendron, Sphinctanthus, and Tocoyena, and confirm their close affinity. The serial classification of Tocoyena does not reflect the evolutionary history of the genus. The paraphyly of T. williamsii with respect to T. pittieri, together with their morphological similarities and geographic distributions, support the inclusion of the former in the latter. Our study calls for additional phylogenetic work on Casasia and the more species-rich genus Randia. While the respective monophyly of both genera is rejected here, future work with a broader representation of Randia is needed.