Trees. Branchlets yellow-green, sparsely pubescent when young. Petiole slender, 1-1.6 cm, pubescent in furrow; leaf blade broadly ovate, ovate, or elliptic, 4-8 × 2.5-5 cm, both surfaces subglabrous, base rounded, rarely rounded-cuneate, margin remotely minutely serrate, apex obtuse or acute; lateral veins 7-9 on each side of midvein. Female inflorescences 5-13 in a panicle, ellipsoid, 1.3-1.5 cm, subsessile; bracts persistent, ca. 4 mm, woody, base cuneate, apex rounded, 5-lobed. Nutlet elliptic, with papery wings ca. 1/3 as wide as nutlet. Fl. Jun-Jul, fr. Aug-Sep.

Treated by J. C. Liao in Fl. Taiwan, ed. 2 as an uncertain species. A. K. Skvortsov indicates that Alnus henryi is very similar to A. formosana, and further studies may show that they are conspecific.

* Taiwan (Tanshui)