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Article from Bean's Trees and Shrubs Hardy in the British Isles
'Rhododendron campylocarpum' from the website Trees and Shrubs Online (treesandshrubsonline.
Shrub or small tree, 1–6.5 m. Leaves 3.2–10 × 1.5–5 cm, orbicular to elliptic, base cordate, glabrous though rarely with a few glands at base. Flowers 3–10(–15), in a lax to more or less dense truss, pale to sulphur yellow, sometimes tinged with red in bud, with or without a basal blotch, campanulate, nectar pouches lacking, 25–40 mm; ovary densely stalked-glandular, style glabrous. Flowering April-May. Royal Horticultural Society (1997).
Distribution Myanmar NE China S Tibet, Yunnan India NE Nepal
Habitat 3,000–4,600 m
RHS Hardiness Rating H5
Conservation status Least concern (LC)
An evergreen shrub 4 to 10 ft high, occasionally taller; branchlets slender, glandular. Leaves 11⁄2 to 4 in. long, about half as wide, mostly elliptic or oblong-elliptic, obtuse or rounded at the apex, usually truncate or slightly cordate at the base, upper surface dark glossy green, lower surface paler glaucous green or even whitish, glabrous on both sides; petiole up to 1 in. long, sometimes reddish, often glandular. Flowers four to nine in a loose terminal cluster, each on a stalk up to 1 in. long, which is usually glandular. Calyx small, glandular-ciliate and usually glandular on the back also. Corolla five-lobed campanulate, 21⁄2 to 3 in. across, varying in colour from creamy white through pale primrose to sulphur yellow, often with a crimson mark in the throat and usually more or less tinged with pinkish buff or apricot in the bud. Stamens ten, glabrous or slightly downy at the base. Ovary densely glandular; style usually glandular in the lower part, never throughout. The specific epithet refers to the curving of the seed-capsule in the fruiting plants seen by Hooker, but often it is straight. Bot. Mag., t. 4968. (s. Thomsonii ss. Campylocarpum)
Native of the Himalaya from Nepal eastward, and of the Mishmi Hills, Assam; discovered by J. D. Hooker in east Nepal late in 1848 and introduced by him. Of all the rhododendrons he saw during his famous expedition, R. campylocarpum was the one he most admired, with its flowers ‘of surpassing delicacy and grace’. It is perfectly hardy in a sheltered place near London but, flowering in April or early May, the display is sometimes spoilt by frost.
R. campylocarpum varies in the colour of its flowers, and in habit. In his Latin diagnosis Hooker described the flowers as white or deep straw-coloured (‘saturate straminea’); in the English text he said: ‘tinged of a sulphur hue and always spotless’. In the beautiful plate accompanying the description, based on his specimens and field-sketches, the flowers are depicted as pale creamy yellow, without blotch (Rhododendrons of the Sikkim Himalaya, t. 30). His account must be based on plants growing near the border between Sikkim and Nepal, northwest of Kangchenjunga, since he was in that area throughout June 1849, the month in which he found the species in flower. But the seeds he sent home were collected in November 1849 and were from a different locality, between Tum-loong and the Cho La, on the frontier between Sikkim and Tibet. Some of the plants raised in Britain from these seeds proved to be remarkably compact, with flowers of a clear yellow and this form was taken by Millais to represent typical R. campylocarpum. To a laxer form commoner in gardens, with pale primrose-yellow flowers, he gave the distinguishing epithet pallidum (Rhododendrons, 2nd series, p. 100; Rhodo. Soc. Notes, Vol. II, p. 73). It should be obvious, however, that what came up from the seeds that Hooker collected ‘blind’ in the early winter of 1849 is really of no botanical relevance, as the species was not described from them, but from wild plants that Hooker had seen in another area.
The name R. campylocarpum “var. elatum” is used in gardens for the form commonest in cultivation, which is tall-growing and has corollas with a red blotch at the base. It is said that in breeding the so-called Hooker form gives mainly yellows, while the “var. elatum” throws pinks and ivory-whites as well as yellows.
subsp. caloxanthum (Balf. f. & Forr.) Chamberlain R. caloxanthum (Balf. f. & Forr.) R. telopeum Balf. f. & Forr.; R. campylocarpum subsp. telopeum (Balf. f. & Forr.) Chamberlain – See R. caloxanthum and R. telopeum, pp. 617–18. This subspecies replaces R. campylocarpum in north-east Burma and adjoining parts of China, but there is some overlap, as already noted by Cowan and Davidian.
R. panteumorphum – The position of this remains in doubt. It may belong to R. × erythrocalyx, for which see this supplement, under R. selense.
R. telopeum f. telopeoides Tagg
R. caloxanthum Balf.f. & Farrer
R. telopeum Balf.f. & Forrest
Leaves sub-orbicular, 1.1–1.7 × as long as broad.
Distribution NE Burma, SW China (SE Tibet, Yunnan).
Awards AM 1934 (L. de Rothschild, Exbury) as R. caloxanthum, from Farrer seed; buds pink, opening deep yellow, suffused red.
Subsp. caloxanthum is generally a smaller plant than is subsp. campylocarpum; the two apparently intergrade in Southern Tibet.
Leaves elliptic, 1.6-2.5 x as long as broad.
Distribution Nepal, NE India, China (S Tibet).
Awards FCC 1892 (Veitch & Sons, Chelsea) as R. campylocarpum; flowers Lemon Yellow.