9. Alnus japonica (Thunberg) Steudel, Nomencl. Bot., ed. 2. 1: 55. 1840.
日本桤木 ri ben qi mu
Betula japonica Thunberg, Nov. Act. Soc. Sci. Upsal. 6: 45. 1799; Alnus japonica var. latifolia Callier; A. maritima (Marshall) Nuttall var. arguta Regel; A. maritima var. japonica Regel; A. reginosa Nakai.
Trees to 20 m tall; bark gray-brown, smooth. Branches dark gray or gray-brown, striate, glabrous; branchlets brown, glabrous or yellow pubescent when young, sometimes resinous glandular. Buds stipitate, with 2 glabrous, ribbed scales. Petiole 1-3 cm, sparsely resinous glandular and pubescent; leaf blade obovate or obovate-elliptic on dwarf shoots, obovate-lanceolate on branchlets, 4-14 × 2.5-4 cm, abaxially sparsely pubescent at first, glabrescent, sometimes resinous glandular and bearded in axils of lateral veins, adaxially glabrous, base cuneate, margin remotely minutely serrate, apex mucronate, acute, or acuminate; lateral veins 7-11 on each side of midvein. Female inflorescences 2-5 in a raceme, ellipsoid, ca. 2 × 1-1.5 cm; peduncle robust, ca. 1 cm; bracts 3-5 mm, woody, base cuneate, apex rounded, 5-lobed. Nutlet obovate, 2-3 mm, with papery wings ca. 1/4 as wide as nutlet. Fl. May-Jul, fr. Jul-Aug.
Temperate forests, streambanks, roadsides; 800-1500 m. Anhui, Hebei, Henan, Jiangsu, Jilin, Liaoning, Shandong, Taiwan [Japan (including Ryukyu Islands), Korea, Russia (Far East)]