Description from Flora of China
Hydrangea arbostiana H. Léveillé; H. yunnanensis Rehder.
Shrubs 1-3 m tall. First year's branchlets brown to dark red-brown, densely yellowish pubescent when young, glabrescent. Second year's branchlets yellowish brown; bark peeled off into irregular fragments. Petiole 1-1.5 cm, slightly crisped pubescent to long pilose; leaf blade abaxially yellow-green and adaxially yellow-brown when dry, oblong to narrowly elliptic, 7-15 × 2-4.5 cm, papery, abaxially subglabrous except pilose along veins and fasciculate pubescent at vein axils, adaxially sparsely minutely strigose with hairs denser and slightly crisped along veins, base cuneate to subacute, margin roughly serrate to serrulate, apex caudate-acuminate. Inflorescences corymbose cymes, 7-10 cm wide, to 14 cm wide in fruit, apex slightly arcuate to truncate; branches 3, unequal with central one usually longer and thicker, densely yellow-brown pubescent. Sterile flowers with sepals 3 or 4, broadly ovate, triangular-ovate, or broadly orbicular, unequal, larger ones 1.3-2.3 × 1.1-3 cm, margin entire or few denticulate, apex subrounded to subacute. Fertile flowers with calyx tube cupular, ca. 1 × 1.5 mm; teeth narrowly lanceolate to triangular-ovate, 0.5-1.5 mm. Petals deep blue, narrowly elliptic to obovate, 2.5-4 × ca. 1 mm, base with a claw 0.5-1 mm, apex obtuse to acuminate. Stamens 8-10, subequal, 1.5-2.5 mm, longer ones not inflexed in bud; anthers broadly oblong to subglobose, 0.5-0.8 mm. Ovary ca. 1/2 superior. Styles 3 or 4, curved outward, 1.5-2 mm in fruit; stigmas enlarged, decurrent along style adaxially. Capsule subglobose, 2.5-3.5 mm in diam., projected apical part 1.2-2 mm, equaling calyx tube. Seeds brownish, obovoid to ellipsoid, 0.5-0.6 mm, wingless; seed coat net veined. Fl. Apr-Jun, fr. Sep-Oct.
* Mixed forests on mountain slopes or in valleys; 1400-2400 m. SC Guizhou, SC Sichuan, Yunnan.