Description from Flora of China
Alnus maritima (Marshall) Nuttall var. formosana Burkill in F. B. Forbes & Hemsley, J. Linn. Soc., Bot. 26: 500. 1899; A. japonica (Thunberg) Steudel var. formosana Callier.
Trees to 20 m tall; bark dark gray-brown. Branches purplish brown, glabrous, striate; branchlets sparsely pubescent. Buds stipitate, with 2 glabrous, ribbed scales. Petiole 1.2-2.2 cm, slender, densely pubescent in furrow; leaf blade elliptic or oblong-lanceolate, rarely ovate-oblong, 6-12 × 2-5 cm, abaxially bearded in axils of lateral veins, adaxially subglabrous, base rounded or broadly cuneate, margin irregularly minutely serrate, apex acuminate or acute; lateral veins 6 or 7 on each side of midvein. Female inflorescence 1, or 2-4 in a raceme, ellipsoid, 1-2.5 cm; peduncle 3-5 mm, robust; bracts 3-4 mm, woody, base cuneate, apex rounded, 5-lobed. Nutlet obovate, 2-3 mm, with papery wings 1/4-1/3 as wide as nutlet. Fl. May-Jun, fr. Jul-Sep.
* Riverbanks, forming pure stands, common; near sea level to 2900 m. Taiwan (Tanshui)