Kindly sponsored by
Peter Norris, enabling the use of The Rhododendron Handbook 1998
Article from Bean's Trees and Shrubs Hardy in the British Isles
'Rhododendron thomsonii' from the website Trees and Shrubs Online (treesandshrubsonline.
Shrub or small tree, 0.6–3.5(–6) m; bark smooth, reddish, peeling; young shoots glabrous or sparsely glandular. Leaves 3–7.5(–11) × 2–5.5(–7.5) cm, orbicular to obovate or elliptic, base rounded to cordate, entirely glabrous (occasionally with a few hairs below), lower epidermis, strongly glaucous-papillate, with some red-stalked glands; petioles glabrous or sparsely glandular. Flowers 3–10, in a lax truss; calyx 2–20 mm, irregular to cupular, often coloured; corolla fleshy, deep crimson, campanulate, with nectar pouches, 35–50 mm; ovary glabrous or glandular, style glabrous. Flowering April-May. Royal Horticultural Society (1997)
Distribution Bhutan China S Tibet India Sikkim, Arunachal Pradesh
RHS Hardiness Rating H5
Conservation status Least concern (LC)
Taxonomic note R. thomsonii hybridizes in the wild with R. campylocarpum (see under R. × candelabrum). Royal Horticultural Society (1997)
An evergreen, glabrous shrub up to 14 ft high and more in diameter in the Cornish gardens. Leaves roundish oval, 2 to 4 in. long, two-thirds as wide, round at the apex except for a short, abrupt tip, and rounded or slightly heart-shaped at the base, dark green above, blue-white or glaucous green below; stalk about 3⁄4 in. long. Flowers borne in March or April, six to ten in a loose terminal cluster; pedicels up to 1 in. long. Calyx 1⁄2 to 3⁄4 in. deep, rarely shorter, cup-shaped, often tinged with red. Corolla bell-shaped, fleshy, rich blood-red, 2 to 3 in. across, five-lobed. Stamens ten, glabrous. Ovary and style glabrous. Bot. Mag., t. 4997. (s. and ss. Thomsonii)
Native of the Himalaya as far west as Nepal; introduced by J. D. Hooker in 1850 from Sikkim, where it grows at 10,000 to 13,000 ft. It first flowered in 1857 with Messrs Methven of Edinburgh, who had taken a scion from one of their seedlings and grafted it on R. ponticum.
R. thomsonii is hardy at Kew, but needs a sheltered position, and even then its flowers and young growths are very liable to injury by late frost. In more favoured gardens it is magnificent, and really deserves a place even in a garden with the climate of Kew, since it makes a handsome specimen and the flowers are so splendid that a display one year in three is ample return for the room it occupies. It received an Award of Garden Merit in 1925.
Crossed with other species, R. thomsonii has given rise to some of the finest and best known hybrid grexes, notably Luscombei (with R. fortunei), Shilsonii (with R. barbatum), and Cornish Cross (with R. griffithianum), ‘Ascot Brilliant’ is an old hybrid between R. thomsonii and a hardy hybrid, raised by Standish over a century ago; more recent commercial hybrids with R. thomsonii as one parent are ‘Sir John Ramsden’ and ‘J. G. Millais’.
subsp. lopsangianum (Cowan) Chamberlain R. lopsangianum Cowan – The distinctive characters of this subspecies are given on pages 786–7, under R. lopsangianum.
The two varieties of R. thomsonii mentioned are considered to be natural hybrids between R. thomsonii and R. campylocarpum – R. × candelabrum Hook.f. – a cross occurring occasionally where the two species are in contact.
R. lopsangianum Cowan
Leaves 3–4.5cm long; calyx 24mm; shrubs 0.6–1.8m.
Distribution China (S Tibet).
Subsp. lopsangianum is in some respects intermediate between subsp. thomsonii and R. sherriffii; some plants in cultivation have a few scattered hairs on the lower leaf surface.
Leaves 5-11cm long, calyx (6-)10-18, shrubs 1.3-6m.
Distribution Nepal, N India (Sikkim, Arunachal Pradesh), Bhutan.
Awards AM 1973 (Crown Estate Commissioners, Windsor); flowers red in throat, darkening at rim.
R. candelabrum Hook, f