The box elder (Acer negundo) is a member of the maple family, but has some features that easily distinguish it from the typical maple. Box elder has use for growing in sites that experience seasonal flooding or have difficulty supporting other tree species. Used in shelterbelts and as a shade tree, the box elder's best ornamental feature is its fruit. The box elder is a cold hardy tree, but also one that can grow into the heat associated with southern climates.
Size and Geography
The sizes of box elder trees range from about 30 feet tall to 60 feet high. The trunks of the largest specimens attain diameters of about 30 inches, according to the "National Audubon Society Field Guide to Trees: Eastern Region." In the wild, box elder trees usually grow near swamps, streams or in floodplains, but it also develops in low-lying hardwood forests. Many escape cultivation, emerging in waste places and along the side of the road throughout the tree's range, which includes much of the East and the northern Great Plains.
One of the most obvious differences between the box elder and other maples is that the former has compound leaves. The leaf's central stem is about 6 inches long, with three to seven separate leaflets growing opposite each other on it, with one at the top of the stem all alone. The leaflets have from three to five teeth on their edges and they grow to between 2 and 4 inches in length. Most box elder trees feature leaves with just three leaflets on them. Their colour is a light shade of green to a medium green tint, with the foliage changing to dull yellow in fall.
Flowers and Bark
Another trait the box elder does not share with most maples is that its flowers develop in hanging clusters on separate female and male trees. The male box elder flowers, as well as the female blooms, are not significantly showy, with a greenish-yellow hue to them. The flowers bloom in March and April, appearing on the twigs before any leaves start to develop. The bark is a brown-grey colour, with the newer growth having a shiny appearance, according to the University of Connecticut Plant Database. The bark on older trees has narrow ridges and furrows.
The seeds of maple trees, called samaras, often develop in back-to-back pairs looking like adjoining keys of a small set of wings. This is true of the box elder, but only the female tree has the samaras. The samaras start out yellowish in September and October, but become tan by winter. They stay on the tree long after the last of the foliage, giving the female trees some interest. However, landscapers sometimes select male box elders to avoid the potentially messy samaras and to keep the possibility of the tree developing new growth around it at a minimum.
- Missouri Botanical Garden: Acer Negundo
- "National Audubon Society Field Guide to Trees: Eastern Region"; Elbert L. Little, Revised 2008 (page 572)