Reorganization of the genus Psychotria and tribe Psychotrieae (Rubiaceae) inferred from ITS and rbcL sequence data

Psychotria is one of the largest genera of angiosperms as currently delimited, with approximately 1650 species estimated worldwide. A molecular phylogenetic study was undertaken using ITS and rbcL sequence data to address the generic circumscription of Psychotria and its allies in the tribe Psychotrieae and to compare traditional subgeneric groupings with relationships inferred from phylogenetic analysis. ITS sequences from 85 taxa were sampled representing the genus Psychotria and members of the tribe Psychotrieae, with Gaertnera and Mitchella used as outgroups. Sequences from the rbcL gene were analyzed for a subset of these taxa, plus genera in the closely related tribes Coussareae, Morindeae, Ophiorrhizeae, and others. Our results suggest that Psychotria is broadly paraphyletic and defined by lack of characters used to define other genera in the tribe. Two groups formerly assigned to Psychotria (sect. Notopleura and subg. Heteropsychotria plus Palicourea) are more closely related to other genera in the Psychotrieae than they are to other species of Psychotria. In addition, subg. Psychotria includes species formerly assigned to the Malesian epiphytic myrmecophytes of subtribe Hydnophytinae. We propose that the genus Psychotria be restricted to include subg. Psychotria, subg. Tetramerae, and members of the subtribe Hydnophytinae.