Hoya buntokensis (Apocynaceae, Asclepiadoideae), a new myrmecophytic species and Hoya wallichii subsp. tenebrosa, a new subspecies from Borneo (Kalimantan, Indonesia)

Abstract

We describe a new Hoya species from Central Kalimantan, H. buntokensis, and a new subspecies of H. wallichii from West Kalimantan, Hoya wallichii subsp. tenebrosa. Hoya buntokensis is part of a group of four species that form specialised leaf structures harbouring ants (here defined as megadomatia), and it is most similar to H. undulata. Hoya buntokensis differs from H. undulata in lamina margin (flat vs undulate); shape of corona lobes outer processes (fan shaped vs elliptic), and in the pollinarium morphology (corpusculum larger than pollinia vs corpusculum smaller than pollinia). Both H. wallichii subsp. wallichii and H. wallichii subsp. tenebrosa are slender plants with ovate to oblong, thinly coriaceous glabrous leaves, slender peduncles with 1 or 2 flowers open at a time, and broadly campanulate corollas. Hoya wallichii subsp. tenebrosa differs from H. wallichii subsp. Wallichii in corolla colour (dark purple with a paler edge vs white-cream), corona lobe shape and surface (broadly elliptic, spreading and with a minute inner process, almost black with a velvety surface vs kidney-shaped, erect and with a well-developed acuminate inner process, purple with a shiny surface).