Acer negundo aka Boxelder

Box elder, Acer negundo, is a deciduous maple also known as ashleaf maple or Manitoba maple. It belongs to the soapberry family, Sapindaceae. Its native range runs from southern Canada through much of the United States and Mexico into Central America. In the wild it grows on stream banks, flood plains, lake shores and swamp edges. It has the widest range of any maple.

In gardens it reaches 30 to 50 feet (9 to 15 m) tall, with a similar spread. Some trees reach 60 to 70 feet (18 to 21 m). The crown is rounded and often irregular. Trees may have several trunks and sprouts along the main stem. It grows very fast, especially when young, but it is short-lived. The thin bark is gray to light brown with shallow, interlacing ridges.

Unlike most maples, box elder has pinnate leaves. Each leaf usually carries three to five toothed leaflets, though some have seven or nine. Three-part leaves on seedlings can look like poison ivy, but box elder leaves sit in opposite pairs. The leaflets are light green above and paler below. Autumn colour ranges from yellow in the north to dull orange-brown in the south. Young twigs are green to purplish with a waxy bloom that rubs off. The buds have white, silky hairs.

Male and female flowers grow on separate trees. Small yellow-green flowers open in March or April, before the leaves. Male flowers hang on long, thin stalks, while female flowers form drooping racemes. Female trees then bear paired, V-shaped samaras about 1 to 1.5 inches (2.5 to 4 cm) long. These turn tan and often stay on the tree through winter. Birds, squirrels and other small mammals eat the seeds.

Box elder suits USDA zones 2 or 3 to about 9, and the RHS rates it H6. It does best in full sun and dislikes deep shade. It accepts clay, sand, loam, poor soils and acid or alkaline conditions. It tolerates drought, urban sites and seasonal flooding. Gardeners use it on difficult sites, in shelterbelts and for stabilising stream banks. Many people prefer male trees because they drop no seed.

The tree has real drawbacks. Its weak, brittle wood breaks in wind, ice and snow. Seedlings sprout freely and can become weedy, and some cities restrict planting. Boxelder bugs feed on female trees and can invade nearby homes in winter. Other pests include borers, aphids, scales, mites and caterpillars. Anthracnose, powdery mildew, cankers, verticillium wilt and trunk decay also occur.

The sap contains sugar, and people boil it down into syrup. Native Americans ate the inner bark and used a bark tea to induce vomiting. Young leaves, seeds and flowers are also edible. However, horse owners should take care. The seeds appear to cause seasonal pasture myopathy, a muscle disease that is often fatal in horses.