Description from Flora of China
Hydrangea heteromalla D. Don var. mollis Rehder; H. mollis (Rehder) W. T. Wang.
Shrubs or small trees, 3-4 m tall. Young branchlets, petioles, and inflorescences slightly yellowish brown to gray-white tomentose. Second year's branchlets dark gray-brown, thick, glabrescent, with oblong lenticels. Petiole thick, 2-8 cm; leaf blade adaxially dark yellow-brown when dry, oblong-ovate to elliptic, 9-22 × 5-11 cm, papery to thinly so, abaxially densely gray-white long tomentose, adaxially sparsely strigose with denser hairs along veins, secondary veins 7-9 on both sides of midvein, base shallowly cordate, broadly truncate, or obtuse, margin densely serrulate, apex acuminate. Inflorescences corymbose cymes, 10-16 cm wide, to 28 cm wide in fruit, apex truncate; branches thick; bracts lanceolate, ca. 2 cm, abaxially densely yellow-brown tomentose. Sterile flowers with sepals 4, broadly ovate to suborbicular, 1.4-2.5 × 1-2 cm in fruit. Fertile flowers with calyx tube campanulate, ca. 1.5 mm, pilose; teeth acutely triangular, 1.5-2 mm. Petals oblong-ovate, ca. 2 mm, base truncate. Stamens 10, unequal; anthers subglobose. Ovary less than 1/2 superior. Styles 3 or 4, erect to slightly spreading, subulate, 1-1.5 mm in fruit; stigmas small. Capsule ovoid-globose to subglobose, 3-4 mm in diam., projected apical part conical, 1.5-2 mm, shorter than calyx tube; persistent calyx teeth narrowly triangular, 1.5-2 mm; persistent styles 3(-5), erect, thick, ca. 1.5 mm, stigmas decurrent. Seeds red-brown to dark brown, narrowly ellipsoid to fusiform, compressed, 1-2 mm, winged at both ends; seed coat striate veined. Fl. Jun-Jul, fr. Sep-Oct.
* Mixed forests or thickets along stream banks in valleys or on mountain slopes; 2500-3500 m. S Sichuan, N Yunnan.