It is a medium-sized deciduoustree, the largest North American species of willow, growing to tall, exceptionally up to, with a trunk diameter. The bark is dark brown to blackish, becoming fissured in older trees, and frequently forking near the base. The shoots are slender and variable in color from green to brown, yellow or purplish; they are brittle at the base, snapping evenly at the branch junction if bent sharply. The foliage buds are long, with a single, pointed reddish-brown bud scale. The leaves are alternate, long, thin, long and broad, usually somewhat falcate, dark, shiny green on both sides or with a lighter green underside, with a finely serrated margin, a short petiole and a pair of small stipules. It is dioecious, with small, greenish yellow to yellow flowers borne on catkins long in early spring at the same time as the new leaves appear. The fruit is a capsule which splits open when mature to release the numerous minute, down-covered seeds. The leaves turn a lemon yellow in the fall. It is typically found along streams and in swamps. Salix gooddingii is sometimes included in S. nigra as a variety, as S. nigra var. vallicola Dudley; when included, this extends the species' range to western North America. However, the two are usually treated as distinct species. Another name occasionally used for black willow is "swamp willow", not to be confused with Salix myrtilloides.
Black willow roots are very bitter, and have been used as a substitute for quinine in the past. Ethnobotanical uses of black willow by various Native American tribes include basketry, and treatment of fever, headache, and coughs. The bark of the tree contains salicylic acid, a chemical compound similar to aspirin. The black willow is the only United Statesnative species to be used as timber for a variety of different items. The black willow lumber is used in furniture and shipping containers. The largest production site for black willow timber was in Louisiana at its peak in the years of 1970. It may also be used as an environmental restorative. Swamp trees in general are, by necessity, good at surviving and thriving in areas where highly mobile environmental toxins are present. Black Willow is very resistant to herbivory and flooding and is also a fantastic erosion control tool. Thus, it is useful for any sort of marshland stabilization or restorative as long as the roots don't penetrate any clay liner that may be in place. In a relatively extensive phytoremediation study, Salix nigra demonstrated some success as a photodegradation tool. Photodegradation is theorized to work by drawing the target chemical up the roots and stem into the leaves where it is degraded by higher energy radiation provided by the sun.
