Phylogenetic inference of Badula (Primulaceae), a rare and threatened genus endemic to the Mascarene Archipelago

With 14 species, Badula (Primulaceae) is the most species-rich endemic angiosperm genus of the Mascarene Archipelago. The relationship between Badula and its ally Oncostemum (c. 100 spp; Madagascar and the Comoros Islands) is uncertain, with implications for the circumscription of Badula as a Mascarene endemic. Within Badula, species rarity (several being critically endangered) and a paucity of herbarium specimens hamper proper species delimitations. Here, we estimate the phylogenetic relationships of Badula based on DNA sequence data from the nuclear ribosomal internal transcribed spacer (ITS) and plastid trnS-trnG-trnG regions with complete taxon sampling of the genus and three samples or more of each taxon. The results strongly supported the monophyly of Badula. Paraphyly of Oncostemum was inferred with weak support; explicit hypothesis testing did not favour this hypothesis over one that forced the monophyly of Oncostemum. Monophyly of several Badula spp. was supported, particularly for taxa from the older islands of Mauritius and Rodrigues. Badula is inferred to have reached the Mascarene Archipelago through a single colonization event. The majority of species segregated into island clades, implying that few, rather than multiple, colonization events have occurred in Badula among the islands of the archipelago.