Aquatic and Wetland Vascular Plants of the Northern Great Plains

Salix L. - Willow

Shrubs and trees of typically wet or moist habitats. Leaves variable in shape, from ovate to lanceolate or linear-lanceolate, or obovate to oblanceolate, the margins serrate, crenate-serrate or entire; petioles glandular or glandular-viscid at the summit in some spp.; stipules persistent or caducous, occasionally lacking. Catkins sessile or on leafy branchlets, erect to pendulous, often precocious; bracts entire, usually pubescent, often apparently ciliate on the margins. Flowers each subtended by 1 or 2 enlarged basal glands; male flowers of commonly 2 or 3-8(12) stamens, the filaments sometimes connate; female flowers each comprised of a 2-carpellary pistil, stigmas 2- or 4-lobed, styles well-developed or none. Capsules 2-valved, sessile or stipitate.

References:

Argus, G.W.  1980.  The typification and identity of Salix eriocephala 
     Michx. (Salicaceae).  Brittonia 32:170-177. 

Dorn, R. D.  1970.  The willows of Montana.  The Herbarium, Dept. of Botany and 
     Microbiology, Montana State Univ., Bozeman.  18 pp. 

Dorn, R. D.  1975.  A systematic study of Salix section Cordatae 
     in North America.  Canad. J. Bot. 53:1491-1522.

Dorn, R. D.  1977.  Willows of the Rocky Mountain states.  Rhodora 79:390-429.

Froiland, S. G.  1962.  The genus Salix in the Black Hills of South 
     Dakota.  Tech. Bull. U.S.D.A.  1269:1-75. 

Raup, H. M.  1959.  The willows of boreal western America.  Contr. Gray Herb. 
     185:1-95.

Lead	Characteristic	Go To
1	Plants with female catkins.	Lead 2
1	Plants vegetative or with male catkins, but with fully expanded leaves.	Lead 19
2	Capsules glabrous (ovary pubescent in S. exigua, but glabrous at maturity).	Lead 3
2	Capsules pubescent.	Lead 13
3	Petioles bearing conspicuous, irregularly lobate glands at or near the attachment to the blade.	Lead 4
3	Petioles lacking glands or sometimes with minute vestiges of glands, or the petioles only glandular-viscid when young (often persistently glandular-viscid in S. fragilis).	Lead 6
4	Leaves ovate-lanceolate, green on both surfaces, paler beneath but not white-glaucous; capsules 4-6.5 mm long at maturity.	Lead 5
4	Leaves elliptic-lanceolate, white-glaucous beneath; capsules 7-10 mm long at maturity.	S. serissima
5	Leaves acute to short-acuminate, dark green and glossy above, thick and rather leathery.	S. pentandra
5	Leaves mostly long-acuminate, bright green and semi-glossy above, not especially thick.	S. lucida
6	Leaves conspicuously or inconspicuously toothed.	Lead 7
6	Leaves entire.	S. pedicellaris
7	Leaves linear-lanceolate, mostly 8-20X longer than wide; rhizomatous shrub often forming dense thickets.	S. exigua
7	Leaves usually less than 10X longer than wide; trees and nonrhizomatous shrubs.	Lead 8
8	Shrubs or small trees up to 5(7) m tall; catkins emerging before or with the leaves, sessile or on short branchlets with a few small leaves; bracts brown to nearly black, persistent after capsule maturity.	Lead 9
8	Trees eventually 10-20 m tall; catkins emerging after the leaves, on leafy branchlets; bracts yellowish-green or pale yellow, deciduous before capsule maturity.	Lead 11
9	Catkins sessile; leaves ovate to obovate.	S. pseudomonticola
9	Catkins sessile or often on short branchlets bearing a few small leaves; leaves lanceolate to somewhat oblanceolate.	Lead 10
10	Twigs gray-brown to dark brown, closely gray-pubescent the first year and often into the second.	S. eriocephala
10	Twigs yellow or yellowish-gray to yellowish-brown, glabrous.	S. lutea
11	Capsules on stipes 1 mm or less long; introduced trees frequently escaping.	Lead 12
11	Capsules on stipes 1-2 mm long; native tree.	S. amygdaloides
12	Twigs olive to brown; petioles glandular-viscid near the summit on vigorous shoots.	S. fragilis
12	Twigs golden-yellow to orange; petioles lacking glands or with minute traces of glands only.	S. alba
13	Catkins emerging and maturing ahead of the leaves.	Lead 14
13	Catkins emerging and maturing with the leaves.	Lead 16
14	Twigs of the previous year gray-pubescent or mostly so; leaves persistently gray-pubescent beneath (rarely glabrate); catkins 1-3(4) cm long; shrub usually of rather dry sites, often where sandy.	S. humilis
14	Twigs of the previous year glabrous (rarely pubescent in S. discolor); mature leaves glabrous beneath at maturity; catkins 2-6(9) cm long; shrubs of wet habitats.	S. discolor
15	Capsules nearly sessile or on stipes to 1 mm long.	S. planifolia
15	Capsules on stipes 1.5-4 mm long.	S. discolor
16	Leaves entire or merely crenate-serrate, the shallow teeth unevenly distributed around the margin.	Lead 17
16	Leaves evenly serrate or mostly so.	Lead 18
17	Leaves persistently white-tomentose beneath, linear-oblong to oblong or narrowly lanceolate; stipes ca. 1 mm long.	S. candida
17	Leaves grayish-pubescent to glabrate beneath, elliptic to narrowly ovate or narrowly obovate; stipes 2-5 mm long.	S. bebbiana
18	Capsules 8-10 mm long, gray-tomentose; leaves somewhat paler green beneath but not glaucous, mostly 2-3.5X longer than wide.	S. maccalliana
18	Capsules 5-7 mm long, closely pubescent mostly toward the base; leaves white-glaucous beneath, mostly 3-6X longer than wide.	S. petiolaris
19	Petioles bearing lobate glands at or near the attachment to the blade; leaves finely glandular-serrate; stamens 3-8(12).	Lead 20
19	Petioles lacking glands or sometimes with minute vestiges of glands, or the petioles only glandular-viscid, in which case the leaves are narrowly lanceolate to lanceolate; leaves serrate or entire, occasionally glandular-serrate; stamens 2, except 4-7 in S. amygdaloides.	Lead 22
20	Leaves ovate-lanceolate, green on both surfaces, paler beneath but not white-glaucous.	Lead 21
20	Leaves elliptic-lanceolate, white-glaucous beneath.	S. serissima
21	Leaves acute to short-acuminate, glossy above, thick and rather leathery.	S. pentandra
21	Leaves mostly long-acuminate, semi-glossy above, not especially thick.	S. lucida
22	Leaves linear-lanceolate, mostly 8-20X longer than wide, entire to remotely serrulate; rhizomatous shrub often forming dense thickets.	S. exigua
22	Leaves broader in proportion to their length; nonrhizomatous shrubs and trees.	Lead 23
23	Leaves acuminate, gradually or abruptly tapered to a long, slender tip.	Lead 24
23	Leaves acute, obtuse, rounded or only short-acuminate at the tip.	Lead 28
24	Leaves dark green and shiny above; twigs often brittle and easily snapping off at the base; introduced trees to 20 m tall.	Lead 25
24	Leaves yellowish-green to dark green and dull above; twigs flexible, not easily snapping off at the base; native shrubs or trees to 12 m tall.	Lead 26
25	Leaves coarsely serrate, with 4-6 glandular teeth per cm of leaf margin; petioles glandular-viscid at the summit; twigs olive to brown.	S. fragilis
25	Leaves more finely serrate, with 7-10 teeth per cm of leaf margin; petioles not glandular-viscid at the summit, or with only minute vestiges of glands; twigs golden-yellow to orange.	S. alba
26	Leaves ovate-lanceolate to lanceolate, mostly long-acuminate with tail-like tips; petioles commonly recurved; branchlets flexuous, somewhat drooping.	S. amygdaloides
26	Leaves lanceolate or somewhat oblanceolate, acuminate; petioles straight; branchlets erect to spreading, not drooping.	Lead 27
27	Twigs gray-brown to dark brown, closely gray-pubescent the first year and often into the second.	S. eriocephala
27	Twigs yellow or yellowish-gray to yellowish-brown, glabrous.	S. lutea
28	Leaves persistently pubescent, especially on the lower surface (rarely glabrate in age in S. humilis).	Lead 29
28	Leaves glabrous or glabrate with age.	Lead 31
29	Leaves elliptic, narrowly ovate or narrowly obovate, sparsely to densely pubescent beneath; leaf margins flat.	S. bebbiana
29	Leaves linear-oblong to narrowly lanceolate or oblanceolate to narrowly obovate, densely pubescent or white-tomentose beneath (rarely glabrate beneath in S. humilis); leaf margins usually revolute.	Lead 30
30	Leaves linear-oblong to oblong or narrowly lanceolate, white-tomentose beneath; leaf margins revolute; shrubs of cold springs or fens.	S. candida
30	Leaves oblanceolate to narrowly obovate, densely pubescent (rarely glabrate) and greenish beneath; leaf margins flat to slightly revolute; shrubs of drier, often sandy habitats.	S. humilis
31	Leaves entire or nearly so, or with a few scattered inconspicuous teeth, sometimes to crenate-serrate with the teeth distributed unevenly around the margins.	Lead 32
31	Leaves mostly serrate or finaly serrate, the teeth evenly distributed around the margins.	Lead 35
32	Small bog shrubs 4-10 dm tall; leaves elliptic-lanceolate to oblanceolate, 2-4.5 cm long, acute to rounded and often apiculate at the tip.	S. pedicellaris
32	Larger shrubs and small trees of various habitats, mostly 2-7 m tall; leaves of various shapes, mostly 3-10 cm long, never apiculate at the tip.	Lead 33
33	Leaves dull grayish-green above, the lower surface usually rugose, with the veins raised prominently on the lower surface (except in var. perrostrata, with the lower leaf surface smooth, without raised veins).	S. bebbiana
33	Leaves bright to dark green above, smooth beneath, only the primary veins, if any, raised on the lower surface.	Lead 34
34	Leaves entire or nearly so, 3-6 cm long; twigs reddish-brown to nearly black, shiny.	S. planifolia
34	Leaves, or at least the larger ones, crenate-serrate, 4-10 cm long; twigs yellowish-brown to dark brown, dull.	S. discolor
35	Stipules persistent, often prominent; leaves ovate to obovate, rounded to cordate at the base.	S. pseudomonticola
35	Stipules lacking or caducous; leaves generally lanceolate, acute to obtuse at the base.	Lead 36
36	Leaves paler below than above, but not glaucous, elliptic-lanceolate to oblanceolate, mostly 2-3.5X longer than wide.	S. maccalliana
36	Leaves white-glaucous beneath, narrowly lanceolate or narrowly oblanceolate, mostly 3-6X longer than wide.	S. petiolaris