Searching for the relatives of Coffea (Rubiaceae, Ixoroideae): the circumscription and phylogeny of Coffeeae based on plastid sequence data and morphology.

The circumscription of Coffeeae (Rubiaceae) and phylogenetic relationships within the tribe were evaluated using sequence data from four plastid regions (trnL-F intron, trnL-F intergenic spacer [IGS], rpl16 intron, and accD-psa1 IGS) and a morphological data set. Eleven candidates for inclusion in Coffeeae were examined using plastid data, and a further three were investigated using morphology alone. Based on previous phylogenetic analysis of the subfamily Ixoroideae, nine genera representing five tribes were used as outgroups. Our results support an enlarged circumscription for Coffeeae, containing 11 genera, viz. Argocoffeopsis, Belonophora, Calycosiphonia, Coffea, Diplospora, Discospermum, Nostolachma, Psilanthus, Tricalysia, Sericanthe, and Xantonnea. The inclusion of Diplospora and Tricalysia within Coffeeae, based on published molecular data, and the inclusion of Argocoffeopsis, Belonophora, Calycosiphonia, Discospermum, and Sericanthe, based on morphological evidence, are well supported. Nostolachma is newly transferred from Gardenieae subtribe Diplosporinae to Coffeeae, and Xantonnea from Octotropideae to Coffeeae. The exclusion of Bertiera from Coffeeae and placement in tribe Bertiereae is supported on the basis of molecular and morphological data. The removal of Diplospora and all other genera from Gardenieae subtribe Diplosporinae to Coffeeae and Octotropideae renders Diplosporinae superfluous. It is proposed that Xantonneopsis be transferred to Octotropideae; Petitiocodon is tentatively placed in Gardenieae. The monophyly of seven genera is supported, but Coffea is identified as paraphyletic in relation to Psilanthus on the basis of molecular and combined molecular and morphological data.