Systematic position of the anomalous genus Cadia and the phylogeny of the tribe Podalyrieae (Fabaceae)

Tribe Podalyrieae is a group of papilionoid legumes that are largely endemic to the Cape Floristic Region of South Africa, possessing fire survival strategies with both nonsprouting and sprouting species. A phylogenetic study of the tribe was undertaken using gene sequences obtained from the internal transcribed spacer (ITS) of nuclear ribosomal DNA as well as the plastid rbcL gene (107 species). Several clades were identified within the tribe. Subtribe Xiphothecinae consists of the genera Amphithalea and Xiphotheca. Subtribe Podalyriinae was paraphyletic. Based on the results of this study, Liparia (except L. calycina) and Podalyria are sister genera with Stirtonanthus sister to both of these. While Podalyria and Stirtonanthus are monophyletic, the monophyly of Liparia is still uncertain. Virgilia and Calpurnia are closely related and Cyclopia retains an isolated, monophyletic position within the tribe. Cadia is monophyletic and sister to the rest of the Podalyrieae. The placement of this genus has, until now, been uncertain due to their actinomorphic flowers that are unusual among papilionoid legumes. The data from this study indicate that actinomorphic flowers may be interpreted as an apomorphy for Cadia and it shares many characters with Podalyrieae. We therefore propose that Cadia be transferred to Podalyrieae from the paraphyletic tribe Sophoreae. The age of the root node of the tribe Podalyrieae s.s. was estimated at 30.5 +/- 2.6 million years (Ma) using nonparametric rate smoothing (NPRS) and 34.7 Ma (confidence intervals: 25.1-44.1 Ma), using a Bayesian relaxed clock, indicating that a major radiation has taken place during the middle to late Miocene and early Pliocene. Finally, we found that nonsprouting species have a higher rate of molecular evolution than sprouting species.