Description from Flora of China
Clethra cavaleriei H. Léveillé; C. cavaleriei var. leptophylla L. C. Hu; C. cavaleriei var. subintegrifolia Ching ex L. C. Hu; C. delavayi var. glabra S. Y. Hu; C. delavayi var. lanata S. Y. Hu; C. delavayi var. yuana (S. Y. Hu) C. Y. Wu & L. C. Hu; C. esquirolii H. Léveillé; C. euosmoda Dop; C. lancilimba C. Y. Wu; C. lineata H. Léveillé; C. longebracteata Sleumer; C. minutistellata C. Y. Wu; C. monostachya Rehder & E. H. Wilson; C. monostachya var. cuprescens W. P. Fang & L. C. Hu; C. monostachya var. lancilimba (C. Y. Wu) C. Y. Wu & L. C. Hu; C. monostachya var. minutistellata (C. Y. Wu) C. Y. Wu & L. C. Hu; C. monostachya var. trichopetala W. P. Fang & L. C. Hu; C. nanchuanensis W. P. Fang & L. C. Hu; C. nanchuanensis var. albescens L. C. Hu; C. purpurea W. P. Fang & L. C. Hu; C. purpurea var. microcarpa W. P. Fang & L. C. Hu; C. sinica K. S. Hao; C. yuana S. Y. Hu.
Trees or shrubs, 1–8 m tall, deciduous. Petiole 0.5–3 cm; leaf blade elliptic, ovate-elliptic, ovate, lanceolate, or oblanceolate, 4.2–15(–24) × 1.4–6(–10.5) cm, papery, abaxially nearly glabrous to densely pubescent, often with stellate-tufted hairs in axils of secondary veins, reticulations not or only slightly raised and usually dark brown, base cuneate to rounded, margin serrate nearly throughout or basal 1/4 entire, teeth 22–50 or more per side on larger leaves, 1–5 mm apart; apex acute to acuminate; secondary veins 7–24 on each side of midvein. Racemes 1(–4) per branchlet, 7–21 cm, densely stellate pubescent, thickest rachis on each twig basally 1.1–2.3 mm wide; bracts acerose, 7–10 mm. Pedicel 3.5–15 mm at anthesis. Sepals lance-ovate to lanceolate, 3.5–6 × 1.4–3.1 mm, densely stellate pubescent, midvein usually distinct at anthesis, apex abruptly mucronate-acuminate. Petals white or reddish pink to dark purple, (4–)5–12 × 2.4–6 mm, abaxially smooth or papillose, adaxially glabrous or basally pilose, margin neither thickened nor apically distinctly fimbriate. Stamens 5–9 mm, included, equal to petal lengths, or exserted; filaments pilose, villous, or occasionally glabrous; anthers 1.0–3.5 mm. Style 4–10 mm at anthesis, glabrous to strigose, apically 3-parted. Fruiting pedicel 0.6–1.7 cm. Ovary and capsule distally hispid, with longer hairs 0.5–1.5 mm; persistent style 7–11 mm. Fl. Jun–Sep, fr. Sep–Oct.
Clethra delavayi is treated here as a single, highly variable species. All characters that have been used to delimit more narrowly defined species in other treatments of Chinese Clethra exhibit a strongly continuous pattern of variation from west to east across the range of the species in China (i.e., leaf size and shape, the number of secondary veins on each side of the midvein, anther size and shape); they also exhibit geographically correlated or seemingly random patterns, but without correlated gaps in character states among any two or more characters (i.e., style pubescence, corolla abaxial surface, stamen exsertion).
Mixed or coniferous forest margins, ± open thickets, slopes to alpine regions; 300–4000 m. Chongqing, Fujian, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangxi, Sichuan, SE Xizang (Mêdog), Yunnan, Zhejiang [Bhutan, NE India, N Myanmar, Vietnam].