Salix nigra (black willow)

General Remarks
Black willow is a tree of eastern North America ranging from central Texas to southern Ontario, Quebec, and New Brunswick (however, absent in northern Maine). Within Massachusetts it is found everywhere except Nantucket and is fairly common in suitable habitats, wherever there is enough light and moisture. Black willow is one of very few native tree willows. It belongs to the primitive section Humboldtianae, where most species are of tropical or subtropical range. S. nigra and S. amygdaloides are the only boreal (northern) representatives of this section. As the latter willow is not known from New England, S. nigra is the only representative of the section in our area. While the majority of willows have "cap-shaped" (calyptrate) bud scales due to connate scale margins, S. nigra features bud scales with distinct margins that overlap on the adaxial side of the bud (the side facing the stem). This is a unique feature among local willows.

Description
Trees up to 20 m or even taller [1], [2], [3]; bark rough, furrowed, blackish brown (which is emphasized in its name), forming wide, thick irregular plates [4]. Branchlets very brittle at base, brown to reddish brown, glabrous to sparsely pilose or even tomentose or densely villous. Buds all looking uniform: small, tawny, glabrous, conical, with pointed apex, positioned at acute angle to shoot [5], [6], with bud scale margins free and overlapping [7].
Leaves broadly to narrowly lanceolate or even nearly linear, 6-25 mm broad, 6-13 times as long as wide; leaf base cuneate, sometimes rounded, margin regularly and minutely glandular-serrulate [8]. Immature leaf blades reddish to yellowish green, translucent, glabrous (sometimes sparsely pilose to densely sericeous); mature blades glabrous to sparsely pilose above, paler green, not glaucous, glabrous or sparcely pilose beneath. Midrib often pilose on both sides; stomata either present or absent on upper surface. Leaf texture very delicate, lateral veins entirely submersed in parenchyma, except for the very origins of lateral veins [9]. Stipules present at least on more vigorous shoots, usually rounded or with apex acute and axis recurved [10]; frequently (50% according to GA) glandular adaxially.
This is a late-flowering willow; flowering is coetaneous, i.e., about simultaneous with the leaf development. Catkins on leafy stalks; stamens numerous (usually 6) [11], [12], pistillate flowers on short stipes and with very short styles [13] [14].

Recognition
This is a tree willow; branchlets very brittle at base; leaves often with stipules, long and narrow, lanceolate, dark green on both sides, frequently pendulous; bud scale with free, overlapping margins, staminate catkins mostly with 6 stamens; ovaries glabrous, borne on short stipes and subtended by deciduous floral bracts.
Black willow is quite special in our area, yet it sometimes becomes confused with vegetative S. eriocephala, which may have leaves of a somewhat similar shape and with large stipules. However, the texture of leaves in these two willows is quite different: leaves are coarse in S. eriocephala and very thin and soft in S. nigra. Black willow can be confused with the alien brittle willow S. x fragilis, which is also a large tree with dark, rough bark, brittle branchlets and lanceolate, serrulate leaves; they however have very different bud structure, stipules, and catkins, as well as leaf texture.
Black willow can be recognized from the distance due to delicate texture of foliage, which produces an impression of a translucent "cloud," especially close to tips of branchlets [15] [16]. On the contrary, the bark on large black willows is very rough, dark, exfoliating in large irregular plates [17].

Habitat
S. nigra is primarily a tree of river banks, pond shores, and floodplains [18], [19], It is not restricted to alluvial habitats and grows wherever light and moisture are sufficient, frequenting perimeter of ponds and lakes, found in swamps, marshes, wet meadows, open fields, and roadside ditches.

Sources and References
1. Argus G.W. 1986. The genus Salix (Salicaceae) in the Southeastern United States. Systematic Botany Monographs 9. 170 pp.
2. Argus G.W. 2006. Guide to the Identification of Salix (Willow) in Illinois, Indiana, Ohio, and Pennsylvania. [https://www.researchgate.net/publication ...]
3. Argus G.W. 2010. Salix L. in Flora of North America North of Mexico, Volume 7. Magnoliophyta: Salicaceae to Brassicaceae, pages 23-162. Eds. Flora of North America Editorial Committee. Oxford and New York: Oxford University Press. Online version: [http://www.efloras.org/florataxon.aspx?f ...]


Last time modified 2016-04-26T10:22:39-07:00 (A.Zinovjev & I.Kadis)