Balf. f. & R.E. Cooper
Description
Rhododendron argipeplum Balf.f. & R.E.Cooper is an eastern Himalayan species of restricted distribution; GBIF records (about 77 occurrences) come from Bhutan, neighbouring northeastern India and adjacent China. It is a shrub or small tree of the cool-temperate forest belt, growing in mixed broad-leaved and conifer forest, rhododendron thickets and along ridges and ravines, generally between about 2700 and 3600 m. The individual photographed at Yatong-La in Bhutan at 3200 m in May, flowering as the higher passes thaw, is typical of its montane setting in the humid, cloud-influenced forests of the eastern range, where deep leaf litter and high atmospheric moisture prevail.
It forms a much-branched shrub up to several metres tall, the young shoots and petioles bristly-setose. The leaves are leathery and elliptic to oblong-ovate, dark green and glabrescent above, and clothed beneath with a thin, often bicoloured indumentum overlying a fawn-coloured felt. The flowers are borne in compact terminal trusses; the corolla is tubular-campanulate, fleshy, and deep red to crimson, usually with darker nectar pouches at the base. There are typically ten stamens, and the ovary bears a glabrous to setose style. The fruit is a woody, curved septicidal capsule splitting to release numerous small winged seeds.
The species belongs to subgenus Hymenanthes, subsection Barbata, a group of red-flowered, setose-stemmed Himalayan rhododendrons in which species delimitation has been debated; it has at times been confused with Rhododendron smithii and allies. Pollination of the showy red corollas is associated with birds and large bees. Owing to its limited eastern Himalayan range and dependence on intact temperate forest, the species is regionally restricted, and like many Bhutanese rhododendrons it is potentially vulnerable to forest clearance and to the pressures of climate change on the narrow montane belt it occupies.
Author: Balf. f. & R.E. Cooper · Sources: POWO (Kew), GBIF, Flora of Bhutan, The Rhododendrons of Bhutan, Flora of China, Royal Botanic Garden Edinburgh revision of subgenus Hymenanthes