An evergreen or semi-evergreen shrub 3 to 8 ft high in the wild; young shoots clad with appressed, flattened, forward-pointing hairs. Spring leaves (those on the lower part of the shoot) elliptic, oblong-elliptic, or ovate, up to 2 in. long and 1 in. or slightly more wide, acute to acuminate at the apex, cuneate at the base, often deciduous; summer leaves (those near the apex of the shoot) leathery, more persistent than the spring leaves, obovate to oblanceolate, up to 11⁄2 in. long and 1⁄2 in. wide; both kinds dull green above, paler beneath, clad on both sides, but more densely beneath, with appressed bristly hairs; the same type of hair covers the petiole, which is about 1⁄4 in. long or slightly shorter. Flowers opening in May, in terminal clusters of two or three, sometimes up to five or six, on densely appressed-bristly stalks up to 3⁄8 in. long. Lobes of calyx ovate or triangular, sometimes as much as 1⁄4 in. long but usually somewhat shorter, ciliate on the margin. Corolla five-lobed, broadly funnel-shaped, up to 2 in. wide on wild plants, coloured in some shade of red, with darker markings on the central or all three upper lobes. Stamens normally ten, rarely eight, never fewer. Ovary appressed-bristly; style glabrous. Bot. Mag., t. 1480. (s. Azalea ss. Obtusum)
Native of southern and central China as far west as Yunnan and as far south and east as Hong Kong; also of Formosa, Burma, Thailand, and bordering territories. According to Wilson it is common in the area of the Yangtse valley from near Ningpo to Mount Omei, in rocky places, on cliffs, and in thin dry woods and thickets. In Burma it is found on both branches of the Irrawaddy above the confluence near Myitkyina, growing on cliffs and rocks along the mainstreams and their tributaries, even where the surrounding vegetation is Indo-Malayan hill jungle, and is often completely submerged during the rainy season. Farrer writes of it as 'smeared like an interminable bloodstain' along both banks of the Ngaw Chang, a tributary of the eastern branch, and Kingdon Ward likened it in flower to 'the glow from an active volcano at night'.
In China, R. simsii has long been valued as a garden plant and was introduced from there to Europe at an uncertain date, but before 1812, in which year Sims figured it in the Botanical Magazine under the erroneous name Azalea indica, from a plant grown by a James Vere. Until the publication of Wilson's Monograph (1921) it was known by that name or as R. indicum, but the true R. indicum is confined to Japan and has flowers with only five stamens; it also differs in its relatively narrower, acute leaves. Wilson observes that up to about 1845 forms of R. indicum were more plentiful in gardens than those of R. simsii, but that from 1850 onwards the former rapidly dropped out of cultivation, their place being taken by the latter, which also usurped their name. The so-called Indian Azaleas derive mainly from R. simsii and are raised in vast quantities every year by Belgian and Dutch growers for indoor decoration during the winter months.
R. simsii in its wild form is rare in gardens and of course very tender. At Wakehurst Place, Sussex, there is a plant raised from seeds collected by Forrest, but under what number is not known. Most of the seeds of R. simsii sent home by Forrest appear to have come from cultivated plants. In the Wakehurst specimen, which received an Award of Merit on May 23, 1933, the flowers are bright rose, nearly 3 in. across, larger than in wild plants; perhaps a hybrid.