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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 macrosepalum' from the website Trees and Shrubs Online (treesandshrubsonline.
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RHS Hardiness Rating H4
A semi-evergreen shrub usually under 3 ft high, of spreading habit; young shoots clad with short, erect, mostly gland-tipped hairs, intermixed with longer, spreading, flattened hairs. Lower leaves deciduous in autumn, mostly oblong or oblong-elliptic, sometimes broadest above or below the middle, up to 21⁄2 in. long and 1 in. wide, acute or acuminate at the apex; persistent leaves smaller, obtuse at the apex; both sorts slightly rugose above, hairy on both sides and on the margins; petioles hairy, up to 1⁄4 in. long. Flowers fragrant, opening in April or May in terminal clusters usually of four to six, but sometimes up to ten; pedicels up to 3⁄4 in. long, glandular. Calyx green, with five narrow, pointed, strap-shaped, hairy lobes 3⁄4 in. to more than 1 in. long. Corolla rose-pink to reddish purple, widely funnel-shaped, 11⁄2 to 2 in. wide, five-lobed, the upper lobes spotted with purple. Stamens usually five, sometimes more numerous. Ovary clad with appressed, white, glandular hairs; style glabrous. (s. Azalea ss. Obtusum)
Native of Japan in Shikoku and the southern half of the main island. It was introduced to Europe by Maximowicz, but apparently did not reach Britain until 1914, when seeds were received which Wilson had collected in Japan. According to him it is common in pine woods and open situations, on its own or with R. kaempferi. It is a quite attractive azalea, easily recognised by the unusually long calyx-lobes, but is not common in gardens. It may be cut back in hard winters, and the flower-buds, which start to swell early in spring, are often damaged by frost; or the buds open prematurely, exposing the individual flowers before they are fully developed.
R. mucronatum var. ripense (Makino) Wils