Phylogenetic structure and clade circumscriptions in the Gardenieae complex (Rubiaceae)

Abstract In this study we investigate the large and diverse Rubiaceae–Gardenieae and closely related tribes Bertiereae, Coffeeae, Cremasporeae, Octotropideae, and Pavetteae. Some of the tribes or groups have been shown to be monophyletic and strongly supported, but the phylogeny of this large complex is still far from being satisfactorily elucidated particularly for Gardenieae, both in terms of intertribal relationships as well as tribal delimitations. We reconstruct the phylogeny of the complex using an extensive sampling of 108 genera and five plastid DNA regions. Phylogenetic relationships demonstrate that Gardenieae sensu Andreasen & Bremer is polyphyletic, as Burchellia, Didymosalpinx, Monosalpinx , and Mantalania are closer to Octotropideae–Cremasporeae. In addition, Pavetteae and the investigated members of Aulacocalyceae are nested in a supported but partially unresolved Gardenieae–Pavetteae clade. Within this clade, several strongly supported groups are resolved: an Aidia group, an Alibertia group, a Gardenia group, Pavetteae including Pelagodendron , a Porterandia group, a Randia group, a Rothmannia group (including Aulacocalyx and Heinsenia ), a Sherbournia group, and the two isolated genera Massularia and Schumanniophyton . The latter genus presented a high rate of genetic substitutions, which resulted in perturbations of the phylogenetic reconstruction. A revised tribal circumscription is given for Gardenieae, the Alibertia group is recognized at tribal level as an emended Cordiereae, and a new tribe, Sherbournieae, is described to accommodate the members of the Sherbournia group.