Morphological and molecular evidence support the inclusion of Mycetia hainanensis in Mouretia (Rubiaceae)

A key diagnostic feature of the genus Mycetia is its berry-like fruits, which distinguish it from its capsular-fruited relatives in the tribe Argostemmateae. However, the fruit character of Mycetia hainanensis H. S. Lo has long remained uncertain, as the species was previously known only from flowering specimens. Our rediscovery of this species at the type locality has now resolved this uncertainty.

We found that M. hainanensis produces fleshy capsules that open via an apical operculum and flowers with a corolla tube shorter than 4 mm long. This finding first prompted a morphological re-evaluation, which indicated that the species aligns more closely with the genus Mouretia. Subsequent molecular phylogenetic analyses of plastid and nuclear DNA data robustly supported this hypothesis, placing the species within Mouretia.

Given the congruent evidence from both morphology and molecular phylogeny, we propose the transfer of M. hainanensis to Mouretia, along with a complete morphological description. As part of this revision, we also provide keys to all genera in the Argostemmateae and to all species in Mouretia, along with a distribution map of the genus.