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Article from Bean's Trees and Shrubs Hardy in the British Isles
'Rhododendron trichostomum' from the website Trees and Shrubs Online (treesandshrubsonline.
Dwarf shrub, 0.3–1(–1.5) m; leaf bud scales usually deciduous. Leaves 1.2–3 × 0.3–0.6 cm, linear to oblanceolate, apex rounded, slightly mucronate to emarginate, margins usually strongly revolute, lower surface covered with 2–3 tiers of dense overlapping scales, the upper tiers usually pale brown, the lowest paler, golden yellow. Flowers many, in a racemose umbel; calyx lobes 1–2.5 mm; corolla white or pink, hypocrateriform, tube 4.5–8(–10) mm, glabrous outside, hairy within; stamens 5(–6); ovary scaly. Flowering May-June. Royal Horticultural Society (1997)
Distribution China Yunnan, Sichuan
Habitat 3,400–4,600 m
RHS Hardiness Rating H4
Awards AM 1925 (A.K. Bulley, Neston). AM 1971 (M. Simmons, Quarry Wood, Newbury) to a clone 'Quarry Wood', as var. ledoides; flowers white, flushed with a shade of red-purple. AM 1960 (Crown Estate Commissioners, Windsor) to a clone 'Sweet Bay', as var. radinum; flowers Tyrian Rose, suffused white to appear soft pink. AM 1972 (Crown Estate Commissioners, Windsor) to a clone 'Lakeside'; flowers white, flushed red-purple. AM 1972 (Mr & Mrs M. Simmons, Quarry wood, Newbury), as var. radianum; flowers red-purple. FCC 1976 (Lady Anne Palmer, Rosemoor Garden Charitable Trust, Torrington) to a clone 'Collingwood Ingram'; flowers red-purple, paler in throat. AGM 1993
Conservation status Least concern (LC)
Taxonomic note This species is allied to R. primuliflorum but may be distinguished by the narrower leaves. R. hedyosmum Balf.f., which differs in its larger flowers, and is only known in cultivation, is probably a hybrid of R. trichostomum. Royal Horticultural Society (1997)
An evergreen shrub 11⁄2 to 4 ft high, usually of rather lax habit; young shoots slender, covered with a mass of scurfy overlapping scales, mixed with which are whitish hairs. Leaves linear-lanceolate, narrow-oblong or narrow-lanceolate, 3⁄8 to 13⁄8 in. long, 3⁄16 to 5⁄16 in. wide, narrowed at both ends, dull green and some times scaly above, paler and with a thick scurf of scales beneath; stalk about 1⁄8 in. long. Flowers in May, densely packed, ten to twenty or even more in a hemispherical cluster 1 to 11⁄2 in. wide; pedicels up to 3⁄16 in. long, usually shorter. Calyx minute (about 1⁄12 in. long). Corolla white, pale pink, or rose-coloured, fading with age, about 3⁄8 in. long and 1⁄2 in. wide, with a tubular base about 1⁄4 in. long which is hairy inside and expands at the mouth into five lobes, outside of corolla sometimes scaly. Stamens five, hidden away in the tube of the corolla, their filaments glabrous or downy. Ovary scaly; style very short, glabrous. Bot. Mag., t. 8831. (s. Anthopogon)
Native of Yunnan and W. Szechwan at altitudes of up to 13,000 ft, usually on open rocky slopes or in pinewoods; discovered by Père Delavay in the mountains above Lankiung, north of Tali. It was probably introduced by Wilson from W. Szechwan in 1908, but the cultivated plants mostly derive from Forrest’s sendings from 1913–14 onwards, and from those of Kingdon Ward and Rock.
R. trichostomum is perhaps the most ornamental of the Anthopogon series and is also of taller and laxer growth than any of the other commonly cultivated species. It is slightly tender in some forms, but is out of place in woodland and should be given a fairly sunny position. In the past fifteen years it has received Awards of Merit on four occasions: May 20, 1960, to clone ‘Sweet Bay’ (from F.20480); May 22, 1972, to clone ‘Lakeside’; both shown by the Crown Estate Commissioners, Windsor Great Park; May 24, 1971, to clone ‘Quarry Wood’; and May 22, 1972, without clonal name; both plants shown by Mr and Mrs Martyn Simmonds, Quarry Wood, Newbury.
A plant raised at Edinburgh from Wilson’s 1208 (the type-collection of R. sargentianum) proved to be distinct and was named R. hedyosmum by Balfour. It is now merged with R. trichostomum or treated as a variety of it – var. hedyosmum (Balf. f.) Cowan & Davidian. The material depicted in Bot, Mag., t. 9202, as R. hedyosmum represents not the original plant but a seedling of it, grown by E. J. P. Magor of Lamellen, Cornwall. This plant does not belong to R. trichostomum in any form, differing in its much larger calyx.
Dr Cullen remarks that ‘several specimens (Kingdon Ward 4465, 5183 and Rock 9134) are from very large, robust plants with large leaves and flowers, and are perhaps hybrids between R. trichostomum and R. primuliflorum’.