Shrub, 0.3–3 m. Leaves 4–12 × 2–5 cm, elliptic to broadly ovate-lanceolate, apex more or less acute; lower surface covered with a one-layered compacted to spongy tomentum that is continuous, or splitting and becoming patchy, and composed of ramiform hairs that are whitish or yellowish at first, sometimes turning deep reddish brown; petioles tomentose at first, later glabrescent. Flowers 10–20, in a dense truss; calyx 0.5–1 mm, lobes rounded; corolla white, often flushed pink, with purple flecks, campanulate, nectar pouches lacking, 30–35 mm; ovary and style glabrous. Flowering April-May. Royal Horticultural Society (1997)
Distribution China SE Tibet, NW Yunnan, SW Sichuan
Habitat 3,350–4,550 m
Conservation status Least concern (LC)
Taxonomic note The two varieties merge into one another, even within a single population. However, those forms occurring at the highest altitudes are generally referable to var. aganniphum. Plants from the Western edge of the range of the species have a silvery, more or less agglutinated indumentum and have been referred to R. doshongense, an apparently slight difference not meriting formal recognition of this species. R. aganniphum hybridizes with R. phaeochrysum and with R. proteioides in the wild. The latter hybrid has been called R. bathyphyllum. Royal Horticultural Society (1997)
An evergreen shrub 2 to 8 ft high in the wild, sometimes a small tree up to 15 ft high; young stems stout, glabrous or almost so. Leaves thick and leathery, elliptic, oblong-elliptic, oblong-lanceolate, or oblong-ovate, 2 to 41⁄2 in. long, 3⁄4 to 2 in. wide, acute or obtuse at the apex, base rounded, obtuse or slightly cordate, dark green and glabrous above, lower surface coated with a close, continuous, often rather spongy felt with a glossy skin, varying in colour from silvery white to fawn or pale yellow; petiole 3⁄8 to 3⁄4 in. long, glabrous. Flowers twelve to twenty in a fairly dense truss, opening in April; rachis up to 5⁄8 in. long; pedicels 3⁄8 to 11⁄2 in. long, glabrous or slightly floccose. Calyx very small. Corolla varying from white to rose, spotted with crimson, five-lobed, funnel-campanulate to cup-shaped, up to 2 in. across. Stamens ten, downy at the base. Ovary glabrous, conoid; style glabrous, with a discoid stigma. Bot. Mag., n.s., t. 147. (s. and ss. Taliense)
R. aganniphum has a wide distribution, from the Muli region of S.W. Szechwan through N.W. Yunnan to the Tibetan side of the Assam Himalaya; discovered by Kingdon Ward in 1913 on the Doker La (Mekong-Salween divide) and introduced by him in the same year. The type of R. vellereum, here included in R. aganniphum, was collected, also by Ward, in Tibet above the Tsangpo river, near Nang Dzong, in the transition zone where forest and alpine scrub gives way to xerophytic vegetation. The flower truss figured in the Botanical Magazine is from a plant raised from KW 5656, the original introduction, collected in the same area, where 40° F. of frost is not uncommon in winter. Seeds sent later by Ludlow and Sherriff are also from this part of Tibet. R. aganniphum is quite a pretty rhododendron but flowers too early for most gardens. In some forms the leaf-indumentum is remarkably thick and spongy.
The synonym R. vellereum should be deleted, this species being included in R. principis (q.v. in this supplement). Nevertheless, if R. vellereum really represents R. principis, which is known only from a single collection, it is not altogether clear why the type of R. aganniphum should not suffer the same fate. In this connection, see the remarks by Cowan and Davidian in the article accompanying Bot. Mag., n.s., t.147 (as R. vellereum).
The description of R. aganniphum on page 590 is based mainly on plants cultivated as R. vellereum, but could really do duty for the typical variety of R. aganniphum, except that there the leaves are relatively broader (length:breadth ratio 1.7–2.5(2.8):1 against 2.7–3.6:1 in R. principis (Rev. 2, pp. 354, 358). However, the Edinburgh revision widens the scope of R. aganniphum, including in it:
var. flavorufum (Balf.f. & Forr.) Chamberlain R. flavorufum Balf.f. & Forr. – Leaf indumentum pale at first but eventually deep red-brown and becoming patchy. Linked to var. aganniphum by intermediates (Rev. 2, p. 355).
In the revision the following are placed in the synonymy of var. aganniphum: R. schizopeplum, R. fissotectum and R. glaucopeplum Balf.f. & Forr.; and R. doshongense Tagg. But of these, all except R. glaucopeplum are really intermediate between it and var. flavorufum, judging from the original descriptions.
R. aganniphum, in the broad sense, is of wide distribution at high altitudes from south-east Tibet through north-west Szechwan to south-west Szechwan, and must be very common, judging from the number of seed-collections by Forrest and Rock. The best forms are of about the same garden value as R. principis.
R. doshongense Tagg
R. glaucopeplum Balf.f. & Forrest
R. schizopeplum Balf.f. & Forrest
Indumentum remaining pale and intact at maturity.
R. flavorufum Balf.f. & Forrest
Indumentum turning deep brown and splitting, becoming patchy at maturity. Royal Horticultural Society (1997)
RHS Hardiness Rating: H6