Morphology and molecular data in phylogenetic fraternity: The tribe Wrightieae (Apocynaceae) revisited

The monophyly and classification of the tribe Wrightieae of the subfamily Apocynoideae (Apocynaceae) are cladistically investigated. Nine taxa from the Wrightieae sensu Leeuwenberg, nine from other Apocynoideae sensu late (s.l., including two from the traditional Asclepiadaceae), and two outgroup taxa from the Plumerioideae (Apocynaceae) were scored for rbcL sequence data and morphological data, mainly floral characters, and analyzed using successive weighting parsimony analysis. The Wrightieae sensu Leeuwenberg are shown to be largely paraphyletic, the constituent taxa being dispersed among four monophyletic clades. Previously not suggested relationships indicated by the study are the association of Pachypodium with Funtumia, Holarrhena, and Mascarenhasia and the position of Beaumontia close to Trachelospermum. A reclassification of the Wrightieae is discussed, in which three of the identified clades are recognized as tribes, the Wrightieae sensu stricto (s.s.), the Nerieae, and the Malouetieae. The support for the Wrightieae s.s. is very strong, as evaluated with Bremer support and bootstrap analysis. The Malouetieae are also strongly supported, but the Nerieae less so. Using potential morphological synapomorphies identified in the study, circumscription of the tribes is discussed. A potential pseudogene of rbcL is reported for Beaumontia.