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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


21. Salicaceae, the Willow Family
2. Salix L. -- Willow
1. Salix alba L. -- White willow
2. Salix amygdaloides Anderss. -- Peachleaf willow
3. Salix bebbiana Sarg. -- Beaked willow
4. Salix candida Fluegee -- Sage-leaved willow, hoary willow
5. Salix discolor Muhl. -- Pussy willow
6. Salix eriocephala Michx. -- Diamond willow, Missouri willow
7. Salix exigua Nutt. -- Sandbar willow, coyote willow
8. Salix fragilis L. -- Crack-willow, brittle willow
9. Salix humilis Marsh. -- Prairie willow
10. Salix lucida Muhl. -- Shining willow
11. Salix lutea Nutt. -- Yellow willow
12. Salix maccalliana Rowlee
13. Salix pedicellaris Pursh -- Bog willow
14. Salix pentandra L. -- Laurel-leaved willow
15. Salix petiolaris Sm. -- Meadow willow
16. Salix planifolia Pursh -- Planeleaf willow
17. Salix pseudomonticola Ball -- Serviceberry willow
18. Salix serissima (Bailey) Fern. -- Autumn willow


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