Hook.
Description
Begonia xanthina is a herbaceous perennial of the eastern Himalaya and adjacent Indo-Burma, recorded from northeastern India, Bhutan, Nepal, southern China and Myanmar, with cultivated occurrences in Belgium and the Netherlands; GBIF holds about 61 georeferenced records. It inhabits shaded, humid evergreen forest, growing on moist rocks, mossy banks, ravine sides and seepage slopes at low to mid elevations, favouring deep shade and the high humidity of monsoon forest. The photographed plant from Gelephu (Galephug) in southern Bhutan at 600 m in October is typical of these warm, wet subtropical foothill forests where it flowers in the post-monsoon season.
It is a rhizomatous, monoecious herb with a stout creeping rhizome and few large basal leaves. The leaves are broadly ovate, markedly asymmetric (oblique) at the base, cordate, often coloured deep green above with reddish or purplish tinting beneath and a long fleshy petiole. The inflorescence is an axillary cyme borne on an erect peduncle, carrying showy nodding flowers; the tepals are yellow, the staminate flowers with four tepals and numerous yellow stamens, the pistillate flowers with an inferior, three-winged ovary bearing unequal wings and twisted bifid stigmas. The fruit is a pendulous winged capsule dehiscing to release minute seeds.
Described by W.J. Hooker, Begonia xanthina is notable as one of the few yellow-flowered Asian begonias, placed in section Platycentrum, and has long been valued in horticulture for its handsome foliage and unusual flower colour. Its monoecious habit and reliance on small generalist insect pollinators are typical of the genus. Restricted to specialised forest microhabitats, it is sensitive to habitat loss, and conservation of intact foothill forest is important for its persistence.
Author: Hook. · Sources: POWO (Kew), GBIF, Flora of China Vol. 13, Flora of Bhutan Vol. 2, Flora of Nepal, Begonias of the Himalaya (Tebbitt)