Prairie Willow

Appearance

Mid shrubs, 0.3-3 m. Stems usually erect, sometimes decumbent; branches tomentose to glabrescent, peeled wood smooth or striate, striae sometimes very dense, to 20 mm; branchlets red-brown or greenish brown. Leaves: stipules usually foliaceous (rarely rudimentary) on late ones; petiole (1.5-)3-7(-12) mm, velvety or pilose adaxially; largest medial blade narrowly oblong, narrowly elliptic, elliptic, oblanceolate, obovate, or broadly obovate, (20-)50-90(-135) × (7-)13-23(-35) mm, 2.3-4-7.5 times as long as wide, margins strongly revolute to flat, abaxial surface with hairs rarely also ferruginous, adaxial slightly or highly glossy, glabrous, pubescent, or pilose (hairs white, sometimes also ferruginous); proximal blade margins usually entire, sometimes serrulate. Catkins: staminate 14.5-34 × 7-19 mm, flowering branchlet 0 mm; pistillate 9-47 (-55 in fruit) × 5.5-19 mm, flowering branchlet 0-4 mm; floral bract 1.2-2 mm. Staminate flowers: filaments glabrous. Pistillate flowers: ovary obclavate; stigmas 0.24-0.33-0.56 mm; ovules 6-12 per ovary. Capsules 7-12 mm. 2n = 38 and 76.

Naming

Salix humilis Marshall var. humilis
Salix humilis var. hyporhysa Fernald
Salix humilis var. keweenawensis Farwell
Salix humilis var. rigidiuscula (Andersson) B. L. Robinson & Fernald

Distribution

Man., N.B., Nfld. and Labr., N.S., Ont., P.E.I., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Va., W.Va., Wis.

Habitat

Dry mixed woods and forests, Picea mariana-lichen woods, Picea glauca-Abies balsamea forests, wet to dry prairies, grassy balds, loess bluffs, sandy stream terraces, coastal barrens, Carex-Typha meadows, fine sand to rocky granitic, gneissic, limestone, and serpentine substrates.

Reproduction

Flowering (north) early March to early June, (south) late January to late April. dioecious, different shrubs will develop either all male (staminate) catkins or all female (pistillate) catkins from the bud scales along twigs of the preceding year. The female florets develop into seed capsules that become light brown at maturity, when they split open to release tiny seeds that are embedded in cottony hairs. These seeds are dispersed by the wind.

The catkins of Prairie Willow attract primarily small bees and flies, including Cuckoo bees (Nomada spp.), Halictid bees (Halictus spp., Lasioglossum spp.), Andrenid bees (Andrena spp.), Syrphid flies, Calliphorid flies, Muscid flies, and others. Among the Andrenid bees, the following species are specialist pollinators (oligoleges) of willows (Salix spp.): Andrena bisalicis, Andrena erythrogaster, Andrena fenningeri, Andrena illinoiensis, Andrena mariae, and Andrena salictaria. These insects seek nectar and pollen from the florets of the catkins.

Predators

Caterpillars of the Striped Hairstreak (Satyrium liparops) eat the foliage.

Many other insects feed on the foliage, bore through the wood, or suck plant juices from willows. The following leaf beetles have been observed to feed on Prairie Willow: Chrysomela knabi (American Willow Leaf Beetle), Chrysomela lineatopunctata, Chrysomela scripta (Cottonwood Leaf Beetle), Crepidodera decora, Crepidodera nana, Cryptocephalus leucomelas, and Disonycha alternata (Striped Willow Flea Beetle). The Prairie Willow is also the preferred host plant for the leafhopper Empoasca humilis. Other insect feeders include the larvae of wood-boring beetles, weevils, the larvae of gall flies, plant bugs, stink bugs, aphids, the larvae of sawflies, and the caterpillars of many moths. Caterpillars of the butterflies Satyrium acadicum (Acadian Hairstreak) and Limenitis archippus (Viceroy) feed on the leaves of willows, as do the caterpillars of the skipper Erynnis icelus (Dreamy Duskywing). Among vertebrate animals, such birds as the Ruffed Grouse and White-Crowned Sparrow feed on the buds and catkins of willows. Other birds, such as the Northern Harrier, Wilson's Warbler, Yellow Warbler, American Goldfinch, Gray Catbird, and Willow Flycatcher, often construct their nests in willow thickets. The twigs and leaves are often browsed by White-Tailed Deer and Elk.