An evergreen shrub of rather open thin habit, 8 or 10 ft high; young shoots, leaves, flower-stalks, calyx, and ovary scaly. Leaves oblanceolate to obovate, usually broadest above the middle, tapered at the base, pointed; 11⁄2 to 3 in. long, 1⁄2 to 11⁄2 in. wide; glossy green above, glaucous beneath; margins and leaf-stalks usually fringed with long hairs when young. Flowers sweetly scented, produced two to four together in May and June. Calyx very small; flower-stalks up to 1⁄2 in. long. Corolla funnel-shaped, 2 to 21⁄2 in. long; white tinged with pink, yellow in the throat, with the five lobes roundish ovate and about 1 in. long. Stamens ten, shorter than the corolla, densely clothed with hairs on the lower half. Ovary six-celled; style well protruded, scaly at the base. Bot. Mag., t. 4457. (s. Maddenii ss. Ciliicalyx)
Native of Assam in the Khasi, Jaintia, and Naga Hills, and of N.W. upper Burma; introduced about 1845 by Gibson (who collected plants for the then Duke of Devonshire) and named after him by Paxton. But it had been discovered in 1815 and previously named by Wallich in 1832. In the south and south-western counties it succeeds well out-of-doors, but in our average climate needs protection in winter. Being easily cultivated and bearing charmingly fragrant flowers, it has long been a favourite. Some beautiful hybrids have been raised from it crossed with R. edgeworthii, e.g., 'Fragrantissimum' and 'Sesterianum'. Crossed with R. nuttallii it is a parent of 'Tyermanii'.
A beautiful form of R. formosum, grown under glass at Edinburgh, received an Award of Merit in 1960. The flowers are flushed with pale orange in the throat and slightly tinged with pink on the outside. There is a similar plant in the Temperate House at Kew.
R. iteophyllum Hutch. R. formosum var. salicifolium C. B. Cl. – This is closely allied to R. formosum but very distinct in appearance, owing to its willowlike leaves, which are linear or linear-oblanceolate and 2 to 35⁄8 in. long and up to 5⁄8 in. wide. Usually they are not or only slightly ciliate at the margins. The corolla may be downy on the outside near the base (as in R. formosum) or glabrous. Bot. Mag., n.s., t. 563.
This species was discovered by J. D. Hooker and T. Thomson during their visit to the Khasi Hills in 1850, and was introduced by Thomas Lobb, the Veitchian collector. It is cultivated outdoors in the mildest parts of the country.
From the Supplement (Vol. V)
var. inaequale C.B.Cl. R. inaequale (C.B. Cl.) Hutch. – Mentioned on page 795 as a species, this has been restored to its original status as a variety of R. formosum. It was originally described by C.B. Clarke from a specimen collected by the younger Hooker in the Khasi hills.
R. iteophyllum, mentioned on page 664 as a species related to R. formosum, is included in it by Dr Cullen. Although it no longer matters, the spelling used is correct, not R. iteaphyllum (cf. Hutchinson in Bot. Mag., n.s., t. 563).
† R. coxianum Davidian – This was described in 1972 from a cultivated plant raised from seeds collected by Cox and Hutchison in 1965 in the Apa Tani valley of the Assam Himalaya (Arunachal Pradesh). See further in Peter Cox, The Larger Species of Rhododendron, p. 224 and plate 31. It is near to R. formosum.