Salix exigua

Narrow-leaf willow


The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (Flowering plants). Class - Magnoliopsida. Order - Salicales. Family - Salicaceae (Willow family). Genus -Salix L. Species - Salix exigua Nutt.

Ecology: Narrowleaf willow ( Salix exigua) may form extremely dense stands, essentially excluding other shrub species. In some areas, narrowleaf willow develops more open, scattered communities with greater shrub diversity. Common associates throughout the range of narrowleaf willow are other willows (Geyer willow (Salix geyeriana), yellow willow (S. lutea), Booth willow (S. boothii)), red-osier dogwood (Cornus sericea), northern gooseberry (Ribes oxyacanthoides), black cottonwood (Populus balsamifera ssp. trichocarpa), water birch (Betula occidentalis), Wood's rose (Rosa woodsii), and prickly rose (R. acicularis). In the Great Basin, common associates include sagebrush (Artemisia spp.), Fremont cottonwood (P. fremontii), saltbush (Atriplex spp.), and pinyon-juniper (Pinus- Juniperus spp.). Floodplain associates include saltgrass (Distichlis spicata), sand dropseed (Sporobolus cryptandrus), sedges (Carex spp.), western wheatgrass (Pascopyrum smithii), and little bluestem (Schizachyrium scoparium). Narrowleaf willow frequently occurs with the invasive shrub saltcedar (Tamarix ramosissima, T. chinensis).


General: Dioecious shrubs or trees, 0.5-6 m tall, forming colonies by root shoots, branches erect, flexible at base; twigs yellow- to red-brown, smooth or sparsely to densely hairy.

Leaves: Alternate, simple, linear to strap-shaped, 3-16 cm long, 0.2-1 cm wide; lower surface glaucous or not, silky or long-soft hairy to nearly smooth, hairs white, upper surface shiny, silky or long soft-hairy to nearly smooth, margins entire or remotely and minutely spiny-toothed, bases wedge-shaped, tips pointed to tapered; leaf stalks without glandular dots at top; stipules leaflike, rudimentary or absent.

Flowers: Unisexual, lacking sepals and petals, borne in catkins which flower as leaves emerge or throughout season, the catkins slender on leafy twigs, floral bracts pale, hairs wavy or straight, female bracts deciduous; stamens 2; ovaries 1, smooth or hairy; styles 0-0.2 mm long.

Fruits: Capsules which split open to release the seeds, each of which is surrounded by a tuft of hairs; stalks 0.2-0.9 mm long.


Fire: Narrowleaf willow is top-killed by fire but readily resprouts from roots, root crowns, and basal stems after fire. It is among the first species to appear following fire. Narrowleaf willow-dominated communities, like other riparian vegetation, may act as natural firebreaks due to the high water table and proximity to surface water present in these areas .

Foragers: Narrowleaf willow provides important browse for livestock; as well as browsed by moose, elk, and to a limited extent, mule deer. Where abundant, it may be important late summer and winter browse for elk. Narrowleaf willow is important and heavily-used browse for beaver.

Pests: This willow is susceptible to twig cankers, tar spot, aphids, willow galls, and scale insects.


Pollination -Pollination: Narrowleaf willow is primarily insect pollinated

Seed Production and Dissemination - Seed production: Narrowleaf willow produces many small seeds with morphological adaptations to enhance dispersal. Flowering and seed production may begin as early as age 2 to 3 years. In general, willow seeds are dispersed primarily via wind and water. Narrowleaf willow seeds are small, fragile, light, and sufficiently aerodynamic to be wind-dispersed. Narrowleaf willow seeds are nondormant and quickly become desiccated if not on a moist substrate. Seed viability beyond 1 week is rare, and viability lasts no longer than 3 weeks.

Seedling Development - Seedling recruitment of narrowleaf willow may be limited by site availability - establishment requires areas that are both close enough to streams for adequate water and yet protected from intense scouring during floods. Seedling mortality also results from herbivory, pathogens, and competition with other seedlings for available resources. Narrowleaf willow seedlings have been characterized as "fast growing". Annual height increases are 12 inches (30 cm), and stem diameter increases at 0.1 inch (2.6 mm). Shoot growth in willow species varies from year to year in response to resource accumulation from the previous year. Snow cover, early season temperatures, and drought may have little visible effect on current year's growth but may reduce shoot growth and rooting success the following year. Willow height growth is most rapid during late afternoon and early evening.

Asexual regeneration- Narrowleaf willow typically develops dense clonal thickets from root sprouts. Stems develop from shoot buds on lateral roots and form extensive spreading colonies. This colonial habit allows narrowleaf willow to dominate riparian sites. Individual narrowleaf willow plants are generally shrub-like, though older individuals may resemble small trees. Clones expand vegetatively along moisture gradients resulting in dispersed and linear clones, with new clones developing progressively closer to moisture sources. Due to potentially high seedling mortality, asexual clones may be largely responsible for narrowleaf willow's success. Because narrowleaf willow reproduces primarily through asexual sprouting, lack of a resident population can limit establishment of narrowleaf willow, even on favorable sites

Species Distribution


E-Flora of British Columbia
In Klinkenberg, Brian. (Editor) 2015. E-Flora BC: Electronic Atlas of the Plants of British Columbia []. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver.

USDA Plants Database
USDA, NRCS. 2017. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.
Distribution Map photo credit

USFS Plant Database
Anderson, Michelle. 2006. Salix exigua. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

Burke Museum of Natural History and Culture
Burke Museum. 2017. Salix exigua [Online]. University of Washington.<br>

Photo credit: 2015, Brian Luther,2012, Robert L. Carr