Hydrangea longifolia Hayata

This species is closely related to Hydrangea involucrata Siebold, from Japan. However, the distinctive, 2-branched hairs of H. longifolia easily differentiate the two species.

Shrubs erect. Branchlets, petioles, leaf blades, and inflorescences densely appressed hairy with both simple and 2-branched hairs. Branchlets dark brown-red, terete or slightly obtusely angled near apex. Petiole thin, 1.5-2 cm; leaf blade lanceolate, 10-20 × 3-4.5 cm, papery, adaxially with more 2-branched hairs than simple hairs, abaxially with fewer 2-branched hairs than simple hairs, secondary veins 8-10 on both sides of midvein, slender, abaxially prominent, base obtuse to cuneate, margin aristate serrulate, apex caudate-acuminate. Inflorescences corymbose cymes, ca. 9 × 11-14 cm; bracts ovate, ca. 2 × 1.5 cm, densely puberulous and enveloping immature inflorescence before falling. Sterile flowers with sepals 4, elliptic to broadly ovate, 1.5-1.8 × 1.1-1.5 cm in fruit. Fertile flowers unknown. Capsule campanulate, ca. 3 × 3.5-4 mm, with simple hairs and a few 2-branched hairs, apex truncate; persistent calyx teeth triangular, ca. 0.5 mm; persistent styles 2, erect to recurved, 1.5-2 mm, distally enlarged. Seeds brown, ellipsoid, compressed, ca. 0.5 mm, winged at both ends; wings 0.2-0.4 mm; seed coat striate veined. Fl. Jan.

* Forests in high mountains. Taiwan.

Hydrangea involucrata Siebold var. longifolia (Hayata) Y. C. Liu; H. strigosa Rehder var. longifolia (Hayata) Chun.

Hydrangea longifolia is a species of flowering plant in the family Hydrangeaceae endemic to Taiwan. It is an erect shrub that flowers in January. It occurs in forests at low to high elevations. It is closely related to Hydrangea involucrata from Japan.