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.
cv. 'Linearifolium'. – An abnormal garden clone with narrowly linear leaves 2 to 3 in. long, usually 1⁄8 to 3⁄16 in. wide, at the middle, tapering gradually to each end. Flowers in a terminal cluster of about three. Corolla with long, narrow lobes of about the same shape as the leaves and up to 11⁄2 in. long, bright rosy lilac, hairy at the base. (R. linearifolium Sieb. & Zucc. (1846), nom. illegit., not Poir. (1808); Azalea linearifolia (Sieb. & Zucc.) Hook., Bot. Mag., t. 5769.)
This unusual and decorative azalea is evidently a sport from R. macrosepalum, and is very distinct in its long, narrow leaves and corolla-lobes. It was introduced from Japan by Standish and first flowered in his nursery at Ascot in 1867. It is hardy at Kew and worth growing for its remarkable aspect.
It has been usual to treat 'Linearifolium' as the nomenclatural type of the species, and to place the normal, wild form under it as a variety – R. linearifolium var. macrosepalum. As it happens, the name R. linearifolium Sieb. & Zucc., given to this garden variety, is illegitimate, and it is therefore correct to adopt the arrangement that accords with common sense, and put the garden variety under the name of the wild species.
R. ripense Makino R. mucronatum var. ripense (Makino) Wils. – Near to R. macrosepalum, but with constantly ten stamens and hairs of ovary eglandular. Native of S. Japan. It is uncertain if the true species is in cultivation. See further on p. 930.