Andersson, Öfvers. Kongl. Vetensk.-Akad. Förh. 15: 117. 1858.
Blue-stem or dewy-stemmed willow
2-7 m, (multistemmed, sometimes forming clones by stem fragmentation).
branches (highly brittle or not at base), red-brown to violet, usually glaucous, glabrous; branchlets yellow-brown, (strongly glaucous or not), glabrous, sparsely velvety, or tomentose.
stipules absent or rudimentary on early ones, foliaceous or rudimentary on late ones, apex acute; petiole convex to flat adaxially, 4-14 mm, velvety adaxially; largest medial blade lorate, narrowly oblong, narrowly elliptic, or narrowly oblanceolate, 47-115 × 8-22 mm, 3.5-7.7 times as long as wide, base cuneate or convex, margins flat to slightly revolute, entire and gland-dotted, serrulate or crenate, apex acuminate, acute, or convex, abaxial surface glaucous, glabrous, sparsely tomentose, or short-silky, hairs wavy, adaxial slightly to highly glossy, glabrous or pilose; proximal blade margins entire or serrulate; juvenile blade yellowish green or reddish, glabrous or sparsely villous abaxially, hairs white.
flowering before or just before leaves emerge; staminate stout or subglobose, 15-34 × 8-22 mm, flowering branchlet 0(-2) mm; pistillate densely flowered, stout or slender, 14-43 × 7-12 mm, flowering branchlet 0-4 mm; floral bract brown or black, 1.3-2.5 mm, apex rounded, abaxially hairy, hairs straight or wavy.
adaxial nectary narrowly oblong to oblong, 0.3-0.8 mm; filaments connate less than to more than 1/2 their lengths; anthers yellow or purple turning yellow, ellipsoid or shortly cylindrical, 0.4-0.7 mm.
adaxial nectary narrowly oblong to oblong, 0.3-0.7 mm; stipe 0.4-1 mm; ovary pyriform, beak slightly bulged below styles; ovules 9-12 per ovary; styles 0.3-0.9 mm; stigmas flat, abaxially non-papillate with rounded tip, 0.15-0.28-0.6 mm.
Flowering mid Mar-mid May. Streams, wet meadows; 1400-3000 m; Ariz., Colo., N.Mex., Wyo.; Mexico (Baja California, Chihuahua, Coahuila, Durango, Sonora).
is very closely related to
. The two are here maintained as separate species primarily because
is a diploid and
a tetraploid, and also because of their largely allopatric ranges (G. W. Argus 2007). Studies of sawflies (
Newman) by P. W. Price (pers. comm.) show that the same species of
can successfully reproduce on either willow. The only morphological character that separates the two is that in
branchlets and branches are very strongly glaucous, whereas in
they are not glaucous. Some plants have weakly glaucous stems (wax not visible except by polishing or only as sparkling crystals); this may be infraspecific variability or evidence of hybridization.
forms natural hybrids with
S. drummondiana, S. geyeriana
: This putative hybrid occurs in Arizona and New Mexico. It is characterized mainly by weakly glaucous branches.