Hook.f.
Description
Hoya globulosa Hook.f. is an epiphytic climber of the eastern Himalaya and adjoining Indochina, recorded from India, Bhutan, China and Vietnam, with scattered cultivated material elsewhere; the GBIF total of about 115 occurrences reflects its moderately frequent presence in warm, humid montane forest. It grows as an epiphyte on mossy trunks and branches, occasionally as a lithophyte, in subtropical to warm-temperate broad-leaved evergreen forest, broadly between 700 and 1800 m. The photographed plant from Zhemgang in central Bhutan at about 910 m, flowering in October, typifies its occurrence in the moist, shaded foothill forests of southern Bhutan during the post-monsoon season.
The species is a robust, woody, climbing or pendent epiphytic vine with stout stems rooting at the nodes and exuding milky latex when broken. The leaves are opposite, thick and coriaceous, large, elliptic to oblong-lanceolate, acuminate, with a stout midrib and prominent, somewhat impressed lateral venation. The inflorescence is a dense, many-flowered, globose, umbelliform cyme on a persistent peduncle — the rounded flower-head giving the epithet globulosa. The flowers are small, with a fleshy, reflexed, hairy-margined corolla, pale yellow to greenish-white often suffused pink, surmounted by the characteristic waxy, glistening, star-shaped staminal corona. Pollen is borne in paired pollinia, and the fruit is a slender, elongate paired follicle releasing plumed seeds.
Hoya (Apocynaceae, subfamily Asclepiadoideae) is a large palaeotropical genus distinguished by its waxy coronate flowers and pollinarial reproduction; H. globulosa belongs to the large-leaved, dense-umbelled Himalayan-Indochinese assemblage. Its bold foliage and tight spherical flower-heads have made it sought-after in specialist Hoya cultivation. As a forest-dependent epiphyte it is potentially threatened by lowland deforestation and collection pressure, although formally unassessed and locally not uncommon within intact forest.
Author: Hook.f. · Sources: POWO (Kew), GBIF, Flora of China, Flora of Bhutan, Flora of British India, Surveswaran et al. — Phylogeny and revision of Hoya