Maple family (Aceraceae)
Description: This tree is 40-80' tall, forming a single trunk up to 2½' across and a globoid to ovoid crown. The trunk bark of mature trees consists of gray ridges that are separated by narrow brown furrows; sometimes the ridges are interlacing. Branch bark is more smooth and gray, while twigs are greenish brown to brown with scattered white lenticels. Pairs of opposite leaves occur along the twigs. Individual leaves are 3-6" long and 3½-7" wide; they are palmately lobed (usually 5 lobes). Each lobe is rather broad at the base, tapering gradually to a pointed tip; there are usually 1-2 large pointed teeth on either side of each lobe. The upper leaf surface is medium to dark green, while the lower surface is slightly more pale; both surfaces are hairless. The slender petioles are light green to pale yellow, terete, and glabrous; they are as long as, or slightly longer than, the adjoining leaf blades.
Norway Maple can be monoecious or dioecious, producing male (staminate) flowers and female (pistillate) flowers on either the same or separate trees. Both types of flowers are produced in umbel-like clusters spanning 2-3" across; each cluster consists of 10-30 flowers. The slender stalks of each corymb are green and either hairless or glandular-hairy. Individual male and female flowers span about 8 mm. (a little less than 1/3") across; each flower has 5 sepals, 5 petals, and a circular central disk that are greenish yellow. Male flowers have 8 fertile stamens, while female flowers have a green pistil with a pair of styles and 8 sterile stamens. Each pistil has a pair of basal wings. The blooming period occurs during mid-spring shortly before, or at the same time as, the unfolding of the leaves. Fertile pistillate flowers are replaced by pairs of samaras (seeds with elongated wings) that are 1½-2" long. The samaras are joined together at the base, forming an angle that is a little less than 180°. Each pair of samaras dangles from a slender pedicel. The samaras become mature during the fall and turn brown; they are distributed by the wind. The woody root system is shallow and widely branching. The deciduous leaves usually turn yellow in the fall.
Cultivation: Norway Maple prefers full sun to light shade, more or less mesic conditions, and a fertile loam or clay-loam soil. It tolerates urban pollution and compacted soil. Because the leafy crown casts a dense shade, grass and other kinds of ground vegetation have difficulty surviving underneath this tree. The fallen leaves also contain phytotoxic chemicals that inhibit the growth and development of other vegetation.
Range & Habitat: Norway Maple has occasionally naturalized in NE Illinois and probably a few counties elsewhere (see Distribution Map). It was introduced into North America from Eurasia as a landscape tree. Habitats consist of areas along roads and vacant lots in urban areas. Even though it may have the potential to be invasive, this tree is often cultivated in such places as areas along streets, lawns, and city parks.
Faunal Associations: The flowers of Norway Maple are cross-pollinated primarily by bees, including honeybees, bumblebees, and Andrenid bees. More generally, maples (Acer spp.) are host plants of the caterpillars of Acronicta leporina (Leporina Dagger Moth) and other moths, the larvae of Anoplophora glabripennis (Asian Long-Horned Beetle) and other long-horned beetles, leafhoppers (Eratoneura spp.), and Neopulvinaria innumerabilis (Cottony Maple Scale). Among vertebrate animals, the seeds and buds are eaten by many species of birds (see Bird Table). The seeds are also eaten by the Black Bear, Raccoon, Gray Squirrel, Fox Squirrel, Eastern Chipmunk, White-Footed Mouse, and Meadow Vole. Leaves and twigs of maples are browsed by White-Tailed Deer, while the Cottontail Rabbit browses the foliage of young saplings.
Photographic Location: The Arboretum at the University of Illinois in Urbana, Illinois.
Comments: There are many cultivars of Norway Maple. Cultivars with unusual characteristics include those with dark purple leaves, variegated leaves, deeply divided feathery leaves, and a tall columnar crown. Because of the similarity of their leaves, it is possible to confuse the Norway Maple with the native Sugar Maple (Acer saccharum), which is also widely cultivated. For Norway Maple, when one of its petioles is broken off at the base, there should be some milky sap visible. In contrast, the petiole bases of Sugar Maple always exude a clear sap. Because they are designed to attract insect pollinators, the flowers of Norway Maple are more showy than those of Sugar Maple and their floral structures are quite distinct. The paired samaras of Norway Maple form nearly a 180º angle, while those of Sugar Maple are less divergent, forming a 90º angle approximately. Norway Maple also differs in the fall coloration of its leaves: they are usually yellow, while the leaves of Sugar Maple are more often orange to red.