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FNA | Family List | FNA Vol. 7 | Salicaceae

2. Salix Linnaeus, Sp. Pl. 2: 1015. 1753; Gen. Pl. ed. 5, 447. 1754.
[name conserved]

Willow, saule [Latin name for willow] Willow, saule [Latin name for willow]

George W. Argus

Shrubs or trees, slightly heterophyllous, clonal or not, clones formed by root shoots, rhizomes, layering, or stem fragmentation; branching sympodial. Stems not spinose. Buds 1-scaled (oily in S. barrattiana), margins connate into calyptra or distinct and overlapping adaxially, scale inner membranaceous layer usually not separating from outer layer, sometimes free and separating). Leaves deciduous or marcescent; stipules persistent, caducous, or absent (varying in presence and size on early and late leaves); petiole glandular-dotted or lobed distally; (blade often more than twice as long as wide, venation usually pinnate, margins entire, crenulate, crenate, serrate, serrulate, or spinulose-serrulate, teeth gland-tipped). Inflorescences axillary or subterminal, catkins, erect, spreading, or ± pendulous, sessile or terminating flowering branchlets, unbranched (except in subg. Longifoliae); floral bract apex entire, erose, 2-fid, or irregularly toothed; pistillate bract persistent or deciduous after flowering. Pedicels present or absent. Flowers: (sessile), perianth reduced to adaxial nectary (rarely also abaxial nectary, then distinct or connate into shallow cup); stamens 1, 2, or 3-10; filaments distinct or connate; ovary (stipitate or sessile), 2-carpellate; ovules (2-)4-24(-42) per ovary; styles usually connate, sometimes distinct distally; stigmas 2, entire or 2-lobed (less than 2 mm). Fruits capsular, (2-valved, obclavate to ovoid or ellipsoid). Seeds: aril present. x = 19.

Species ca. 450 (113 in the flora): North America, Mexico, West Indies, Central America, South America, Europe, Asia (Malaysia), Africa, Atlantic Islands; mostly in arctic, boreal, and temperate regions; introduced in Australasia, Oceania.

SELECTED REFERENCES Argus, G. W. 1973. The Genus Salix in Alaska and the Yukon. Ottawa. [Natl. Mus. Nat. Sci. Publ. Bot. 2.] Argus, G. W. 1986. The genus Salix in the southeastern United States. Syst. Bot. Monogr. 9. Argus, G. W. 1986b. Studies in the Salix lucida Muhl. and S. reticulata L. complexes in North America. Canad. J. Bot. 64: 541-551. Argus, G. W. 1995. Arizona Salicaceae: Willow family. Part two: Salix. J. Arizona-Nevada Acad. Sci. 29: 39-62. Argus, G. W. 1997. Infrageneric classification of Salix L. in the New World. Syst. Bot. Monogr. 52. Argus, G. W. 2007. Salix L. (Salicaceae): Distribution maps and a synopsis of their classification in North America, north of Mexico. Harvard Pap. Bot. 12: 335-368. Azuma, T., T. Kajita, J. Yokoyama, and H. Ohashi. 2000. Phylogenetic relationships of Salix (Salicaceae) based on rbcL sequence data. Amer. J. Bot. 87: 67-75. Dorn, R. D. 1976. A synopsis of American Salix. Canad. J. Bot. 54: 2769-2789. Dorn, R. D. 1977b. Willows of the Rocky Mountain states. Rhodora 79: 390-429. Dorn, R. D. 1997. Rocky Mountain Region Willow Identification Field Guide. Denver. Raup, H. M. 1943. The willows of the Hudson Bay Region and the Labrador Peninsula. Sargentia 4: 81-135. Raup, H. M. 1959. The willows of boreal western America. Contr. Gray Herb. 185: 1-95.


Key to Subgenera of Salix

1 Bud-scale margins distinct, overlapping; stamens 3-7[-9]; pistillate bracts deciduous after flowering (except S. floridana, sometimes S. bonplandiana); usually trees.   2a Salix subg. Protitea, p. 30
+ Bud-scale margins connate; stamens usually 2, sometimes 1 (3-10 in sect. Salicaster); pistillate bracts persistent (except in sect. Salicaster and in subg. Longifoliae); shrubs or trees   (2)
       
2 (1) Stamens 3-10; pistillate bracts deciduous after flowering.   2b Salix subg. Salix (sects. Salicaster and Triandrae), p. 38
+ Stamens 2 or 1; pistillate bracts persistent after flowering (except in subg. Longifoliae, S. alba, and S. euxina)   (3)
       
3 (2) Pistillate bracts deciduous after flowering; leaf blades usually linear to narrowly elliptic; catkins sometimes branched; syllepsis common; plants clonal by root shoots; petioles not glandular distally.   2c Salix subg. Longifoliae, p. 50
+ Pistillate bracts persistent after flowering (except in S. alba and S. euxina); leaf blades usually not linear, rarely narrowly elliptic; catkins not branched; syllepsis uncommon; plants not clonal by root shoots (except S. setchelliana); petioles glandular or not distally   (4)
       
4 (3) Petioles usually glandular-lobed or -dotted distally; branches and branchlets brittle at base.   2b Salix subg. Salix (in part), p. 38
+ Petioles not glandular distally or glands simple, spherical; branches flexible at base (sometimes brittle in subg. Vetrix)   (5)
       
5 (4) Buds arctica-type or transitional or alba-type; catkins arising from subterminal buds (sects. Chamaetia, Herbella, Myrtosalix) as well as lateral buds; shrubs 0.005-6 m; juvenile blade hairs usually white, rarely ferruginous (in S. athabascensis); pistillate catkins always on flowering branchlets; largest medial blades (relatively broad) 0.8-5.5 times as long as wide; ovaries sometimes glaucous (sects. Chamaetia, Diplodictyae, Myrtilloides, Ovalifoliae), hairs sometimes flat and ribbonlike (sect. Myrtosalix); most staminate and some pistillate flowers with abaxial and adaxial nectaries; inner membranaceous bud-scale layer not separating from outer layer.   2d Salix subg. Chamaetia, p. 60
+ Buds alba-type or intermediate; catkins arising from lateral buds (subterminal buds vegetative); shrubs or trees, 0.1-20 m; juvenile blade hairs mostly white, sometimes ferruginous; pistillate catkins sessile or borne on flowering branchlets; largest medial blades (relatively narrower) 0.7-13.7 times as long as wide; ovaries not glaucous, hairs not flat and ribbonlike; staminate and pistillate flowers usually without abaxial nectaries; inner membranaceous bud-scale layer sometimes distinct and separating from outer layer.   2e Salix subg. Vetrix, p. 93

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