Tinadendron, nouveau genre de Rubiaceae, Guettardeae de Mélanésie orientale

The genus Tinadendron Achille (Rubiaceae, Guettardeae) is described to accommodate two species from New Caledonia and Vanuatu, formerly attributed to the genus Guettarda L. The new genus is distinctive among the other paleotropical dioecious taxa by its inflorescence whose mode of ramification is strictly dichasial. Furthermore it shows the following characters: male and female inflorescence with numerous flowers, imbricate aestivation corolla, non-fibrous, thinly fleshy mesocarp, and pluriloculary osseous endocarp. Tinadendron noumeanum (Baill.) Achille does not remain any more but in one population, located within the remainders of sclerophyllous forest of Baie de Tina at Nouméa, and very threatened by the urbanization and the fires; its placement in the category CR according to the criteria of the IUCN is proposed. Tinadendron kajewskii (Guillaumin) Achille is rather frequent in the rain forest on Maré (Loyalty Islands); its distribution extends to the South of Vanuatu, where it was mistaken for a species related to Antirhea subg. Mesocarpa. A key to the paleotropical genera of Guettardeae, a key to the species of Tinadendron as well as a taxonomic treatment and complete specific descriptions are presented.