Hoya thuathienhuensis and Hoya graveolens (Apocynaceae, Asclepiadoideae), a new species and a new record for the Flora of Vietnam

A new species from the Annamite mountain range of central Vietnam, Hoya thuathienhuensis, is here described and illustrated. Its flowers bear similarity with Hoya lockii, a taxon recently described from the same area with which it shares the reflexed corolla and the thin coriaceous laves. Hoya lockii is an epiphytic shrub, whereas H. thuathienhuensis is a strong climbing liana. We also report the noteworthy extension into southern Vietnam of Hoya graveolens, a taxon previously considered to be endemic of Thailand.