Shrubs or trees, 5-15 m. Stems: branches flexible at base, brownish or yellow-green, highly glossy, glabrous; branchlets yellow-green, red-brown, or brownish, glossy, glabrous. Leaves: stipules absent or rudimentary on early ones, rudimentary or foliaceous on late ones, apex rounded; petiole deeply to shallowly grooved adaxially, 5-15 mm, with pairs or clusters of spherical glands distally or throughout, glabrous adaxially; largest medial blade hypostomatous, narrowly elliptic, elliptic, or lanceolate, 50-135 × 20-50 mm, 2-4 times as long as wide, base convex, margins slightly revolute or flat, serrulate, apex acuminate, abaxial surface pale not glaucous, glabrous, adaxial highly glossy, glabrous; proximal blade margins entire or serrulate; juvenile blade reddish, glabrous abaxially. Catkins: staminate 27-81 × 9-13 mm, flowering branchlet 9-21 mm; pistillate moderately to densely flowered, slender or stout, 29-68 × 7-15 mm, flowering branchlet 9-42 mm; floral bract 2-4 mm, apex acute or rounded to truncate, entire or toothed, abaxially sparsely hairy (mainly proximally), hairs wavy or straight. Staminate flowers: abaxial nectary 0.6-1.7 mm, adaxial nectary square, ovate, or oblong, 0.5-1.5 mm, nectaries distinct or ± connate and cup-shaped; stamens 4-10; filaments distinct, hairy on proximal 1/2; anthers ellipsoid or globose, 0.5-0.6 mm. Pistillate flowers: (abaxial nectary present or absent), adaxial nectary oblong, square, or ovate, 0.4-0.8 mm, (nectaries distinct or connate and shallowly cup-shaped), shorter than or equal to stipe; stipe 0.5-1.6 mm; ovary pyriform, beak bulged below or tapering to styles; ovules 18-22 per ovary; styles connate or distinct, 0.4-0.6 mm; stigmas flat, abaxially non-papillate with rounded tip, or slenderly cylindrical, 0.4-0.6 mm. Capsules 6-9 mm. 2n = 76. Flowering late May-mid Jun. Shores of streams and lakes, marshes, roadsides, waste places; 0-2300 m; introduced; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que., Sask.; Alaska, Colo., Conn., D.C., Ill., Iowa, Ky., Maine, Md., Mass., Minn., Mont., Nebr., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.Dak., Vt., Va., Wis., Wyo.; Eurasia. The Ohio occurrence is based on information from T. Cooperrider (pers. comm.).

Only pistillate plants of Salix pentandra are known to occur in the flora area.