Description from Flora of China
Alnus jackii Hu.
Trees to 10 m tall; bark gray or gray-brown, smooth. Branches dark gray-brown, glabrous; branchlets gray-brown, yellow pubescent. Buds stipitate, with 2 glabrous, ribbed scales.
Leaves obovate-oblong, oblanceolate-oblong, or oblong, 6-16 × 2.5-7 cm, abaxially resinous glandular, glabrous except bearded in axils of lateral veins, adaxially glabrous, base
subrounded, subcordate, or broadly cuneate, margin remotely minutely serrate, apex acute or acuminate to caudate; lateral veins 6-13 on each side of midvein. Female inflorescences 2-4
in a raceme, oblong, 1-2.5 × 1-1.5 cm; peduncle 1-2 cm, glabrous; bracts 5-7 mm, woody, base cuneate, apex rounded, 5-lobed. Nutlet broadly ovate, 3-4 × 2-2.5 mm, with papery wings ca.
1/4 as wide as nutlet. Fl. May-Jun, fr. Jul-Aug.
Forests on mountain valleys, riverbanks; 200-1000 m. Anhui, Fujian, N Guangdong, Guizhou, S Henan, Hubei, E Hunan, Jiangsu, Jiangxi, Zhejiang [Japan].