Shrubs, sometimes small trees, 1.5–3(–5) m tall; young branches brownish purple, cylindric, densely dark brown scaly. Petiole not grooved, 15–30 mm, densely scaly; leaf blade leathery, oblong-elliptic, 11–19 × 3.5–8 cm; base rounded, sometimes slightly cordate to auriculate; apex acuminate; abaxial surface dirty white; adaxial surface sparsely scaly when young, glabrescent; midrib raised abaxially, concave adaxially. Inflorescence terminal, umbellate, 3–4-flowered; bud scales falling off early. Flowers fragrant. Pedicel stout, 1.2–2 cm, densely scaly; calyx lobes ovate, 8–12 mm, persistent in fruit, 1.5–1.8 cm, scaly at base; corolla broadly campanulate, white, 9–11 cm, outer surface scaly; lobes rounded; stamens 10(or 11 or 15), shorter than corolla tube; filaments pubescent below; anthers ca. 8 mm; ovary 5-locular, densely scaly; style slightly exserted from corolla tube, basal half scaly; stigma discoid. Capsule cylindric, lobes keeled, 45–55 mm. Fl. May.

Rhododendron excellens was originally described as having 15 stamens, which does not agree with this description. One solution would be to describe those plants with 10(–11) stamens as a new taxon, which could be called “var. decandrum”. This would account for the vast majority of the specimens available. It is possible that the type of R. excellens was a chance hybrid between “var. decandrum” and R. maddenii subsp. crassum. In Vietnam, where the distribution of “var. decandrum” overlaps with that of R. nuttallii (which it closely resembles), there appear to be intermediates between the two taxa.

Evergreen broad-leaved forests or thickets; 1100–2400 m. S Guizhou, SE Yunnan [N Vietnam].