A phylogenetic study of the tribe Sipaneeae (Rubiaceae, Ixoroideae), using trnL-F and ITS sequence data

The genera of tribe Sipaneeae have been either included within tribe Rondeletieae or treated as its sister tribe, and historically placed in subfamily Cinchonoideae. The herbaceous habit was the only character used to separate Sipaneeae from Rondeletieae. Recent molecular phylogenies included Maguireothamnus, Sipanea, Sipaneopsis, and Neobertiera in Sipaneeae, and positioned the tribe in subfamily Ixoroideae. These results stimulated a detailed analysis of this tribe and an evaluation of the position and delimitation of several genera believed to be related because of their morphological similarity. Our study indicates that tribe Sipaneeae is monophyletic, and confirms its placement within Ixoroideae. The Sipaneeae clade included Chalepophyllum, Dendrosipanea, Limnosipanea, Maguireothamnus, Neobertiera, Sipanea, and Sipaneopsis. Several genera of this group are small shrubs, and the woody habit is shown to be basal in Sipaneeae. Sipanea and Limnosipanea are shown to be monophyletic and not sister taxa, indicating that the herbaceous habit evolved two times in the tribe. Sequences of Steyermarkia, Pteridocalyx and Neblinathamnus were not available in this study, but because of overall morphological similarity with the genera of Sipaneeae, they are tentatively included in the tribe.