Small tree, 8 m high. dbh. 12 cm. Outer bark dark brown with deep vertical cracks; inner bark reddish brown. Leaf: young shoots densely covered with orange-brown hairs; twigs dark brown. Flower: greenish-yellow.
Trees to 9 m tall, usually shrubby in secondary forest, ca. 2 m tall; branchlets hirtellous to glabrous. Stipules ovate-lanceolate, 4-6 mm; petiole 5-12 mm, sparsely pubescent, apex bilateral with 2 glands; leaf blade elliptic, narrowly ovate, oblong-elliptic, obovate, or oblanceolate, 6-12 × 3.5-6 cm, leathery, glabrous and lucid adaxially, sparsely pubescent along nerves abaxially, base rounded or cuneate, margin entire or sparsely shallowly dentate, apex rounded to acute. Male flowers axillary in ca. 2.5 × 0.4 cm spikes; bracts ovate-triangular, ca. 1 mm, pubescent outside; sepals usually 4, oblong-ovate; stamens 2-4, longer than sepals. Female flowers: sepals 4-6, triangular, margins ciliate; ovary ovoid, densely pubescent, bilocular; ovules 2 per locule. Capsules ellipsoid, 1-1.3 cm, pubescent, 2-seeded. Seeds subovate, ca. 9 × 5.5 mm. Fl. and fr. almost throughout year.
Alnus dioica Roxburgh, Fl. Ind., ed. 1832, 3: 580. 1832; Aporosa aurita (Tulasne) Miquel; A. chinensis (Champion ex Bentham) Merrill; A. leptostachya Bentham; A. microcalyx (Hasskarl) Hasskarl; A. microcalyx var. chinensis (Champion ex Bentham) Müller Argoviensis; A. microcalyx var. intermedia Pax & K. Hoffmann; A. roxburghii Baillon; Scepa aurita Tulasne; S. chinensis Champion ex Bentham; S. stipulacea Lindley; Tetractinostigma microcalyx Hasskarl.
Type for Alnus dioica Roxb. Catalog Number: US 3068142 Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany Verification Degree: Original publication and alleged type specimen examined Preparation: Pressed specimen Collector(s): W. Gomez Locality: Sillet., India, Asia-Tropical