Manitoba Maple (Acer negundo), as the species is called in Canada, also known as Ash-leaved Maple or (confusingly) Box Elder in the United States, is a species of maple, which occurs throughout most of North America.

It is a small, usually fairly short-lived tree that grows up to 10-20 m tall, with a trunk diameter of 30-50 cm, rarely up to 1 m diameter. The shoots are green, often with a whitish to pink or violet wax coating when young. Unlike most other maples (which usually have palmate leaves), it has pinnate leaves with usually five (sometimes three or seven) leaflets, resembling an ash or an elder, hence the two alternative common names; the leaves are 12-25 cm long, with each leaflet 6-10 cm long and 3-7 cm wide. No other maple ever has more than three leaflets. The flowers are small and with no petals, 10-30 together on drooping racemes 10-20 cm long, produced in early spring. The seeds are paired samaras, each seed slender, 1-2 cm long, with a 2-3 cm incurved wing; they are wind-dispersed. Unlike most other maples, the tree is dioecious, so each tree grows only one gender of flower and both a "male" and "female" tree are needed for either to reproduce.

A few botanists treat it in its own distinct genus, as Negundo aceroides, but this is not widely followed.

There are two subspecies:

• The typical subspecies Acer negundo subsp. negundo, with hairless shoots and leaves, in most of its area: southeast British Columbia east to southern Ontario and New Hampshire, and south to eastern Nevada, Arizona, northernmost Mexico and southeast to Florida. 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.
• The western subspecies Acer negundo subsp. californicum, with pubescent (finely hairy) shoots and leaves; a disjunct population in the Central Valley area of California.

Ecology

This species prefers bright sunlight. It often grows on floodplains and other disturbed areas with ample water supply. 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 to be an invasive species in some areas of the continent.

Several birds and some squirrels feed on the seeds; notably the Evening Grosbeak uses them extensively. The Maple Bug (also known as Boxelder bug) lays its eggs on all maples, but prefers this species.

Cultivation and uses

Acer negundo is rarely planted as a landscape tree; its weak wood, irregular form, and prolific seeding make it a poor choice for most areas. It often is found in landscapes in some areas due to it reproducing from the many seeds produced.

There are some cultivars, including some variegated forms, that are available in the nursery trade.

Although its wood is considered undesirable for most uses, this tree has been considered as a commercial source of wood fibre, for use in fibreboard.

References and External links

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• Maeglin, R. R. & Ohmann, L. F. (1973). Boxelder (Acer negundo): A Review and Commentary. Bull. Torrey Bot. Club 100 (6): 357-363.
• Acer negundo images at bioimages.vanderbilt.edu

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