Sp. Pl. 2: 1019. 1753.
Shrubs, 1–3 m. Stems: branches brownish, not glaucous, pubescent to glabrescent, (peeled wood often with very dense striae, to 21 mm); branchlets redbrown or yellowbrown, (weakly glaucous), sparsely tomentose. Leaves: stipules foliaceous, apex acute or convex; petiole convex to flat adaxially, 2–9 mm, velvety adaxially; largest medial blade obovate, broadly obovate, or elliptic, 27–85 × 14–35 mm, 1.5–2.8 times as long as wide, base convex or cuneate, margins slightly revolute, entire, remotely or irregularly serrate, or crenate, (glands submarginal), apex acuminate or convex, abaxial surface glaucous, pubescent or pilose, hairs (white, sometimes also ferruginous) spreading or erect, wavy or crinkled, adaxial dull or slightly glossy, pubescent or pilose to glabrescent, veins more hairy, (hairs white, sometimes also ferruginous); proximal blade margins entire; juvenile blade reddish or yellowish green, densely tomentose to glabrescent abaxially, hairs white. Catkins flowering before leaves emerge; staminate subglobose or globose, 15.5–21.5 × 10–15 mm, flowering branchlet 0.5–4 mm; pistillate loosely to moderately densely flowered, 15–37 × 9–20, flowering branchlet 2.5–7 mm; floral bract brown, tawny, or bicolor, 1–2.2 mm, apex acute or tapering and rounded, abaxially hairy, hairs straight. Staminate flowers: adaxial nectary oblong or square, 0.3–0.7 mm; filaments distinct, glabrous or hairy on proximal 1/2 or basally; anthers purple turning yellow, ellipsoid or shortly cylindrical, 0.5–0.8 mm. Pistillate flowers: adaxial nectary oblong or square, 0.3–0.7 mm, shorter than stipe; stipe 1.4–2.6 mm; ovary pyriform, densely short-silky, hairs wavy or crinkled, beak sometimes slightly bulged below styles (long-beaked); ovules 10–12 per ovary; styles 0–0.3 mm; stigmas broadly cylindrical, 0.25–0.37–0.5 mm. Capsules 4–13 mm. 2n = 76, 38.
Phenology: Flowering early Apr-early Jun.
Habitat: Wet thickets, swamps
Elevation: 10-300 m
Introduced; Mass., Pa., Europe
"-0.5mm" is not declared as a valid unit of measurement for this property.