Description from Flora of China
Shrubs, 2(–5) m tall; branches many and fine, densely shiny brown appressed-setose, setae flat. Summer and winter leaves different. Petiole 2–6 mm. Leaf blade ovate, elliptic-ovate or obovate to oblanceolate, 1.5–5 × 0.5–3 cm; base cuneate or broadly cuneate; margin slightly revolute, finely toothed; apex shortly acuminate. Inflorescence 2–3(–6)-flowered. Pedicel ca. 0.8 cm, densely shiny brown appressed-setose; calyx deeply lobed; lobes triangular-long-ovate, ca. 5 mm, coarsely appressed-hairy, margin ciliate; corolla broadly funnelform, rose, bright to dark red, or white to rose-pink, with dark red flecks on upper lobes, 3.5–4 × 1.5–2 cm, lobes obovate, 2.5–3 cm; stamens 10, ca. as long as corolla, filaments pubescent below; ovary ovoid, 10-locular, densely shiny brown-strigose; style exserted, glabrous. Capsule ovoid, up to 10 mm, densely strigose, calyx persistent. Fl. Apr–May, fr. Jun–Aug.
Rhododendron chaoanense T. C. Wu & P. C. Tam (Med. Mat. Guangdong 4: 35. 1978), described from Guangdong, is apparently close to, and possibly a hybrid of, R. simsii, but differs from that species in its obscure calyx lobes, 7 stamens, and long-exserted style.
Rhododendron simsii var. albiflorum R. L. Liu (Acta Bot. Yunnan. 15: 190. 1993), described from Jiangxi, is probably no more than an albino form of R. simsii.
Rhododendron simsii var. strigosostylum G. Z. Li (Guihaia 15: 298. 1995 [“strigoso-stylum”]), was described from Guangxi and said to differ from var. simsii in having a corolla rose-pink to red, with minute lobes ca. 2 × 1 mm, and a style silky-strigose below. The present authors have seen no material, but, from the original description, it seems likely that this entity is a hybrid of the widely cultivated R. simsii.
Rhododendron simsii has been used widely in horticulture as a parent of both the “pot azalea” cultivars and a range of cultivars grown in the warmer parts of China.
Pinus massoniana forests, forest margins, open upland thickets; 500–2700 m. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangsu, Jiangxi, Sichuan, Taiwan, Yunnan, Zhejiang [Japan, Laos, Myanmar, Thailand].