Xanthophytum antoanense (Rubiaceae, Ophiorrhizeae), a new species from Vietnam

<i>Xanthophytumantoanense</i> is described as a new species endemic to Central Vietnam. It is morphologically closest to <i>X.capitatum</i> in having setose hairs on the abaxial leaf surface and a pedunculate head-like inflorescence but differs from the latter by a number of characteristics: shorter stem, 3-lobed stipules, narrowly lanceolate leaf blades with a cuneate-oblique base and 20-22 pairs of secondary veins, 3.5-4.5 cm long peduncle, spatulate calyx lobes, larger corollas with a 5-5.4 mm long tube and 2.4-3 mm long lobes, and an apically hairy style. A detailed description, an illustration, and information on distribution, ecology and phenology, and a provisional assessment of the conservation status of the new species are provided.