Robert H. Mohlenbrock. USDA SCS. 1989.
Midwest wetland flora: Field office illustrated guide to plant species
. Midwest National Technical Center, Lincoln. Provided by USDA NRCS Wetland Science Institute (WSI).
Nuttall, N. Amer. Sylv. 1: 75. 1842.
Shrubs or trees,
branches gray-brown, red-brown, or yellow-brown, villous, or tomentose to glabrescent; branchlets yellowish, yellow-brown, or red-brown, pubescent or puberulent, tomentose, short- or long-silky villous.
stipules absent or rudimentary on early ones, foliaceous or rudimentary on late ones; petiole 1-5(-10) mm, pubescent or puberulent, villous, or short-silky adaxially; largest medial blade (sometimes hypostomatous), linear or lorate, (glands marginal), 30-136-143 × 2-14 mm, 6.5-28(-37.5) times as long as wide, base cuneate, margins slightly revolute, entire or remotely spinulose-serrulate, apex acuminate or acute, abaxial surface glaucous (sometimes obscured by hairs), densely long-silky, villous or pilose to glabrescent, hairs appressed or spreading, straight or wavy, adaxial slightly glossy, sparsely or densely long-silky to glabrescent; proximal blade margins entire; juvenile blade yellowish green, densely long-silky-villous abaxially.
staminate 7-54 × 2-10 mm, flowering branchlet 1.5-56 mm; pistillate loosely to densely flowered, slender or stout, 14.5-70 × 3-12 mm, flowering branchlet 2-55 mm; floral bract 1.2-2.6 mm, apex acute, convex, or rounded, entire or erose, hairs wavy, straight, or crinkled, abaxially hairy throughout or proximally, or glabrate.
abaxial and adaxial nectaries present and distinct; filaments hairy on proximal 1/2; anthers (sometimes reddish turning yellow).
adaxial nectary oblong, ovate, or flask-shaped, relative adaxial nectary/stipe length variable even within same catkin; stipe 0-0.9 mm; ovary obclavate or pyriform, glabrous, pilose, or villous, or sometimes beak hairy, beak bulged below or abruptly tapering to styles; ovules 12-30 per ovary; styles (sometimes distinct), 0-0.5 mm; stigmas flat, abaxially non-papillate with rounded tip, or 2 plump lobes, 0.1-0.5 mm.