Sm.
Description
Rhododendron arboreum is the tree rhododendron of the Himalaya and the broader Indian subcontinent, ranging from Pakistan through India, Nepal, Bhutan and Myanmar into southwestern China, with a notable disjunct presence in the hills of Sri Lanka; widely cultivated, it appears in GBIF from many temperate countries and totals nearly 3000 occurrences. It is the most familiar species of the genus across its native range, growing in temperate broadleaved and oak-laurel forest, on hill slopes and in scrub, here recorded at Nundhaki in Nepal at 1400 m and in Bhutan. Spanning a broad elevational band, it flowers conspicuously in late winter and spring (March), painting Himalayan hillsides crimson.
It is an evergreen shrub or tree reaching 10-20 m, with a gnarled trunk and rough, flaking bark. The leaves are leathery, oblanceolate to elliptic, dark glossy green above and clothed beneath with a dense silvery, fawn or rusty indumentum that varies between subspecies. The flowers are massed in dense, rounded, terminal trusses of 15-20; each corolla is tubular-campanulate, 3-5 cm long, ranging from deep blood-red through pink to white, the throat marked with darker nectar spots. Stamens are typically 10, and the ovary tomentose with a long style. The fruit is a curved, woody, ribbed capsule splitting to release numerous small winged seeds.
Described by James Edward Smith, the species belongs to subgenus Hymenanthes, subsection Arborea, and is highly variable, with several recognised subspecies (e.g. subsp. cinnamomeum, subsp. nilagiricum, subsp. zeylanicum) differing in leaf indumentum and altitude. It is the national flower of Nepal (lali gurans) and the state tree of Uttarakhand, and the nectar-rich corollas are sought by sunbirds and bees, with the flowers used to make a local beverage. Although widespread and not globally threatened, lower-elevation populations face pressure from fuelwood harvesting, grazing and forest conversion.
Author: Sm. · Sources: POWO (Kew), GBIF, Flora of Bhutan, Flora of China, The Genus Rhododendron (Cullen & Chamberlain monograph)