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Peter Norris, enabling the use of The Rhododendron Handbook 1998
Article from Bean's Trees and Shrubs Hardy in the British Isles
'Rhododendron neriiflorum' from the website Trees and Shrubs Online (treesandshrubsonline.
Shrub or small tree, 1–6 m. Leaves 4–11 × 1.9–3.2 cm, elliptic to oblong or oblanceolate, lower surface glabrous with a glaucous, strongly papillate epidermis; petioles sparsely floccose-tomentose or glabrescent, rarely setose-glandular. Flowers 5–8(–12), in a tight truss; calyx 2–15 mm, cupular when well-developed; corolla fleshy, crimson to light red, occasionally straw yellow, tubular-campanulate, with nectar pouches, 35–45 mm; ovary densely tomentose, sometimes also with at least some glands, tapering into the glabrous style. Flowering April-May. Royal Horticultural Society (1997)
Distribution Bhutan Myanmar NE China S Tibet, W Yunnan India NE
Habitat 275–3,350 m
RHS Hardiness Rating H6
Conservation status Least concern (LC)
An evergreen shrub or small tree up to 25 ft high; young shoots reddish, woolly at first. Leaves oblong to narrowly obovate, rounded to abruptly tapered at both ends, mucronate, 2 to 4 in. long, 1 to 11⁄2 in. wide; dark green above, glaucous-white beneath, glabrous except on the midrib beneath; stalk 1⁄3 to 3⁄4 in. long, reddish and downy when young. Flowers six to twelve in a truss 3 to 4 in. wide, opening in March or April; pedicels about 1⁄2 in. long, downy. Calyx membranous, varying in size and very irregular, with five unequal rounded lobes. Corolla rich crimson, tubular-bell-shaped, 11⁄2 to 13⁄4 in. long, not so much wide, with five rounded, notched lobes. Stamens ten, white, glabrous, 3⁄4 to 11⁄4 in. long; anthers very dark brown. Ovary felted; style slightly overtopping the stamens, glabrous except just above the ovary. Bot. Mag., t. 8727. (s. and ss. Neriiflorum)
Native of mid-Yunnan westward through upper Burma to the eastern Himalaya, where it reaches almost as far as Bhutan. It was discovered by Père Delavay in the Tali range, Yunnan, and introduced from the same area by Forrest in 1910 (F.6780). Here, at least on the eastern flank of the range, where there is little forest, it makes a shrub 2 to 8 ft high, occurring in open pinewoods, shaded gullies, or rocky pastures, at 10,000 to 12,000 ft. The seeds of the original introduction were taken from low-growing plants and produced dense, very free-flowering bushes, but these eventually grew much taller than the parental wild plants, e.g., to 10 ft high at Werrington Park in Cornwall.
Plants of Tali provenance are rare in gardens. Mostly, the cultivated stock derives from seeds collected farther west, where R. neriiflorum, though often a dwarf shrub at subalpine elevations, is more commonly taller growing, and sometimes a small tree. These plants, once usually known by the synonymous name R. euchaites, make erect, rather lax shrubs up to 15 ft high. The flowers are usually of the purest crimson-scarlet and borne in great profusion in late March, April, or May. Out of flower, the species is easily recognisable by its neat, oblongish leaves, glaucous white beneath. It is perfectly hardy in light woodland south of London, and received an Award of Merit when shown from Bodnant on March 26, 1929.
A form of R. neriiflorum with leaves tapered at the apex, a fewer-flowered inflorescence, and smaller calyx, was introduced by Farrer and Cox in 1919 from the pass above Hpimaw, Burma, on the Salween-Nmai Hka (Irrawaddy) divide. It was given specific status as R. phoenicodum Balf. f. & Farrer, but should probably be regarded as part of the normal variation of the species. It is figured in Bot. Mag., t. 9521.
subsp. phaedropum (Balf.f. & Farrer) Chamberlain R. phaedropum Balf.f. & Farrer – See R. phaedropum, mentioned under R. neriiflorum (page 727).
Although occurring in Yunnan this is, in the main, the east Himalayan expression of R. neriiflorum, found as far west as Bhutan.
As for subsp. neriiflorum but with lower leaf surface reticulate, forming alveoli with some papillae horizontal.
Distribution China (W Yunnan).
R. euchaites Balf.f. & Forrest
R. phoenicodum Balf.f. & Farrer
Pedicels, calyx and ovary lacking glands; leaves 4-9cm, 1.7-3× as long as broad, plane below, lacking reticulations.
Distribution NE Burma, China (SE Tibet, W Yunnan).
Awards AM 1929 (Lady Aberconway and Hon. H.D. McLaren, Bodnant) as subsp. euchaites; flowers a rich ruby red.
Taxonomic note (incl. R. euchaites Balf.f. & Forrest & R. phoenicodum Balf.f. & Farrer)
Pedicels, calyx and ovary with at least some glands; leaves 8-11cm, 3-5(-7)x as long as broad, plane below.
Distribution Bhutan, NE India (Arunachal Pradesh), China (S Tibet, W Yunnan).
The status of subsp. agetum is uncertain, even though the cited difference is striking. Subsp. neriiflorum merges with the more Westerly subsp. phaedropum where the distributions of the two meet.