Evolutionary relationships in the Spermacoceae alliance (Rubiaceae) using information from six molecular loci: insights into systematic affinities of Neohymenopogon and Mouretia

Abstract

Several recent phylogenetic studies of Rubiaceae have dealt with enigmatic taxa whose systematic positions have been previously unknown or controversial. We address evolutionary relationships in the Spermacoceae alliance (Rubioideae) with special emphasis on the Asian genera Mouretia and Neohymenopogon, here sequenced for the first time. Both genera belong in the tribe Argostemmateae and have persistent calyx lobes on the fruit in common with Argostemma and Mycetia. Other previous uncertainties are resolved with strong support; Saprosma is sister to Paederieae s. str. and Carpacoce is sister to remaining Anthospermeae. Our results further reveal some phylogenetic problems. Danaideae is sister to remaining taxa in the Spermacoceae alliance with high posterior probability, which contradicts results in a recent study. The uncertainty concerning evolutionary relationships of Dunnia and Theligonum is reinforced, despite a denser taxon sampling in the Spermacoceae alliance compared with earlier studies. We also demonstrate yet another example of the controversial correlation between molecular substitution rate and plant life history.