Morphological phylogenetic analysis of the Astronieae (Melastomataceae)

The Astronieae represent one of the earliest diverging clades of the pantropical family Melastomataceae and are endemic to the rainforests of southeast Asia and the Pacific islands. They comprise about 150 species of trees and shrubs in four currently accepted genera: Astrocalyx, Astronia, Astronidium, and Beccarianthus. A prior phylogenetic analysis focused on the Astronieae but sampling was insufficient to draw conclusions about generic circumscriptions or species-level relationships. Moreover, family-wide molecular phylogenetic analysis revealed that Tessmannianthus from tropical America has a closer relationship with the Astronieae than the Neotropical Merianieae, where it was originally placed. This study presents the first phylogenetic analysis of the tribe based on morphological data. Parsimony analyses of 57 ingroup taxa with 205 morphological characters were conducted to test support for the monophyly of each constituent genus and to verify the placement of Tessmannianthus within the Astronieae. Characters were partitioned into discrete and continuous datasets to assess potential areas of incongruence; the latter was coded with the differential gap-weighting method. The global analysis yielded two equally most parsimonious trees, the strict consensus of which shows that Astrocalyx, Astronia, and Astronidium are each monophyletic. Beccarianthus is biphyletic, consisting of one clade with oblong anthers and another with linear anthers, the latter being restricted to New Guinea. Likewise, Astronia section Astigmata was found to be polyphyletic. Intergeneric relationships within the tribe are well-resolved but these need further confirmation and support. Tessmannianthus forms a monophyletic genus that groups within the Merianieae. However, the partitioned analysis of discrete dataset suggests that Astronia sect. Astigmata is monophyletic with a single reversal and that the Astronieae are sister to Tessmannianthus except T. cereifolius. The phylogeny of the Astronieae sensu stricto supports the evolutionary change from axile to ascending and bilobed basal-axile placentae, and ultimately into collapsed ones. The resurrection of Bamlera to accommodate the Papuasian Beccarianthus clade is proposed.