Acer negundo is a species of maple native to North America. Box Elder, Boxelder Maple, and Maple Ash are its most common names in the United States. Other variant names -- some of which are obviously regional - include Ash Maple, Ash-leaf Maple, Black Ash, California Boxelder, Cutleaf Maple, Cut-leaved Maple, Negundo Maple, Red River Maple, Stinking Ash, Sugar Ash, Three-leaved Maple, and Western Boxelder. In Canada it is known as Manitoba Maple. In Russia it is called American Maple (американский клён).
The names "Box Elder" and "Boxelder Maple" are based upon the similarity of its whitish wood to that of boxwood and the similarity of its pinnately compound leaves with those of some species of elder. This is the only North American maple with compound leaves.
These names include (but are not limited to) Ash-, Cut- or Three-leaf (or -leaved) Maple, Ash Maple, Sugar Ash, Negundo Maple, and River Maple.
Common names may also designate a particular subspecies. For example, a common name for A. negundo subsp. interius may be preceded by "Inland" (as in "Inland Boxelder Maple"). A common name for A. negundo subsp. californicum may be preceded by "California" or "Western".
The shoots are green, often with a whitish to pink or violet waxy coating when young. Branches are smooth, somewhat brittle, and tend to retain a fresh green colour rather than forming a bark of dead, protective tissue. The bark on its trunks is pale gray or light brown, deeply cleft into broad ridges, and scaly.
Unlike most other maples (which usually have simple, palmately lobed leaves), Acer negundo has pinnately compound leaves that usually have three to seven leaflets. Simple leaves are also occasionally present; technically, these are single-leaflet compound leaves. Although some other maples (such as A. griseum, Acer mandshuricum and the closely-related A. cissifolium) have trifoliate leaves, only A. negundo regularly displays more than three leaflets.
The flowers are small and appear in early spring on drooping racemes 10-20 cm long. The seeds are paired samaras, each seed slender, 1-2 cm long, with a 2-3 cm incurved wing; they drop in autumn or they may persist through winter. Seeds are usually both prolific and fertile.
Unlike most other maples, A. negundo is fully dioecious and both a "male" and "female" tree are needed for either to reproduce.
Some authors further subdivide subsp. negundo into a number of regional varieties but these intergrade and their maintenance as distinct taxa is disputed by many. Even the differences between recognized subspecies are probably a matter of gradient speciation
Finally, note that a few botanists treat Boxelder Maple as its own distinct genus (Negundo aceroides) but this is not widely accepted.
This species prefers bright sunlight. It often grows on flood plains and other disturbed areas with ample water supply, such as riparian habitats. Human influence has greatly favoured this species; it grows around houses and in hedges, as well as on disturbed ground and vacant lots.
Although native to North America, it is considered an invasive species in some areas of that continent. It can quickly colonize both cultivated and uncultivated areas and it has become naturalized in eastern China. The range is therefore expanding both in North America and elsewhere. It can also be found in some of the cooler areas of the Australian Continent where it is listed as a pest invasive species.
Although its light, close-grained, and soft wood is considered undesirable for most uses, this tree has been considered as a commercial source of wood fibre, for use in fibreboard.