Vincetoxicum phucanhense (Apocynaceae, Asclepiadoideae), a new species from Vietnam.

Vincetoxicum phucanhense (Apocynaceae, Asclepiadoideae), a new species from Vietnam, is described, illustrated, and compared with three morphologically similar species: Vincetoxicum flexuosum (R.Br.) Kuntze, V. harmandii (Costantin) Meve & Liede, and V. tengii (Tsiang) Meve & Liede. V. phucanhense differs from V. flexuosum in having shorter pedicels, very sparsely hairy sepal margins (vs. glabrous), a larger corolla, broadly elliptic pollinia (vs. globose), longer fruits, and longer seeds. It also differs from V. harmandii in having shorter petioles, smaller leaf blades, glabrous adaxial leaf surfaces (vs. hairy), and a larger corolla. In comparison with V. tengii, V. phucanhense can be distinguished by its larger corolla, corolla coloration (yellow, pink, or red vs. greenish), and broadly elliptic pollinia (vs. globose). A key to the 14 species of Vincetoxicum recorded in Vietnam is provided.