Alnus glutinosa (L.) Gaertn.

Tree to c. 15 m high (to c. 20 m in cultivation). Bark dark brown, strongly fissured. Young shoots glabrous but glandular-viscid. Winter buds short-stalked, purplish. Petiole 7–15 mm long, often purplish. Lamina 4–10 × 2.5–10 cm (to 14 × 13 cm on vigorous vegetative shoots), broadly oblong to obovate, plicate in bud, hairy on veins beneath at first, soon glabrous except for tufts of axillary hairs, serrulate to coarsely serrate, lobulate on basal vegetative shoots; veins in 6–7 pairs, prominently raised beneath; base usually cuneate; apex rounded to retuse. Buds stipitate, not enclosing ♀ catkins in winter. ♂ catkins 3–8 together behind shoot apices, 2.5–7 cm long (to 12 cm in cultivation), cylindric, opening in spring before lvs; peduncles to c. 5 cm long; bracts peltate, purplish; anthers yellow. ♀ catkins 3–7 together behind shoot apices, c. 5 mm long, glandular. Cone (1)–1.3–1.7–(2) cm long, ellipsoid; scales becoming horizontal after dehiscence and persistent on tree. Nutlet c. 3 mm long, broadly ovoid; wing narrower than nut.

[From: Webb et al. (1988) Flora of New Zealand. Volume 4.]