A semi-deciduous, twiggy azalea usually from 3 to 8 ft high; young shoots very slender, clothed with appressed, flattened, forward-pointing hairs, of a grey or greyish-brown colour. Leaves lanceolate to oblanceolate, 1⁄3 to 11⁄2 in. long, 1⁄16 to 2⁄5 in. wide, toothless, furnished on both surfaces with appressed hairs; stalk very short. Flowers in clusters of two to six, or solitary, on short pedicels. Calyx very small, clad with white hairs. Corolla funnel-shaped, about 11⁄2 in. wide, lilac-purple. Stamens five to ten, shorter than the corolla, downy at the base. Ovary bristly; style glabrous. Seed-vessel egg-shaped, 1⁄3 in. long, covered with appressed hairs, the calyx persisting at the base. Bot. Mag., n.s., t. 52. (s. Azalea ss. Obtusum)
Native of S. Japan, on Shikoku, Kyushu, and the southern part of the main island; also of some mountains farther to the north-east, west of Mt Fuji. It reached this country through the Arnold Arboretum, to which Wilson sent seeds from Shikoku in 1914. He wrote of it: 'I have seen a few flowers, but the colour is not attractive, though doubtless in spring when covered with blossoms, the plant would have a charm of its own.' It is in fact a very pleasing species, but more than one plant is needed if it is to make an effective display. It is hardy in woodland south of London, but uncommon in cultivation. As in most members of the Obtusum subseries, the upper leaves on the annual shoots (the so-called summer-leaves) are much smaller than the 'spring-leaves' borne lower on the shoot, which are mostly shed in winter.
R. komiyamae, included in R. tosaense by Rehder, is recognised as a distinct species by Japanese botanists, differing in having flowers with ten stamens against normally five in R. tosaense in the narrow sense. Plants of this nature are said to be confined to two mountains to the west of Mt Fuji.