Sugar Maple
Acer saccharum
Maple family (Aceraceae)

Description: This tree is 60-100' tall at maturity and its trunk is 2-3' across. In relatively open areas, the densely branched crown is globoid to ovoid in shape. Saplings that are growing in dense shade, however, have a narrow open crown with only a few ascending branches. Trunk bark is gray to gray-brown and it is covered with relatively flat irregular plates. These plates have a rough texture. Branch bark is gray and more smooth, while twigs are brown and glabrous with scattered white lenticels (air pores). Non-woody young shoots are light green and glabrous. Pairs of opposite leaves occur along the twigs and young shoots. Individual leaves are 3-5" long and similarly across; each leaf has 3-5 palmate lobes and an orbicular outline. The tips of these lobes are pointed, while their sinuses are rounded; the sides of the terminal lobe are more or less parallel. The margin of each leaf is often slightly undulate and it has a few large teeth that are dentate. The upper leaf surface is dark green and glabrous, while the lower surface is pale to medium green, glabrous (or nearly so), and sometimes slightly glaucous. However, there is a variety of Sugar Maple (var. schneckii) in southern Illinois and areas further south that has leaves with softly pubescent undersides. The slender petioles are 2-4" long, light green, and glabrous; less often, they may be pubescent or slightly red.

Sugar Maple is either dioecious or monoecious, producing separate male and female flowers on the same or different trees. Male flowers are produced in drooping umbels or sparingly branched corymbs about 3-4" long. Individual male flowers are about 1/8" (3 mm.) long, consisting of a yellowish green calyx with 5 teeth and a variable number of exerted stamens (usually about 6-8). Female flowers are also produced in drooping umbels or sparingly branched corymbs, but they are shorter (about 1-2" long). Individual female flowers are about 1/8" (3 mm.) long, consisting of a yellowish green calyx with 5 teeth and a 2-celled ovary with a divided style. Both male and female flowers can occur in the same inflorescence. The long slender pedicels of both male and female flowers are quite hairy. The flowers bloom during mid- to late spring as the leaves emerge (which are yellowish green at this time of year). Cross-pollination occurs by the wind during a 1-2 week period. Fertile female flowers are replaced by paired samaras that become mature during the fall. The paired samaras form a 60 to 90 angle with each other. Individual samaras are about 1" long, consisting of a single-seeded head with a membranous wing; they are distributed by the wind. The woody root system consists of much-branched lateral roots that are relatively shallow. During the autumn, the deciduous leaves assume brilliant shades of yellow, orange, or red.

The preference is full sun to light shade, well-drained mesic conditions, and a fertile loamy soil, although soil containing rocky material, sand-loam, silt-loam, or clay-loam is also tolerated. Young saplings of Sugar Maple are able to survive in moderately dense shade, although higher levels of light are preferred. Generally, this tree doesn't tolerate flooded conditions for any substantial length of time. Sugar Maple is somewhat susceptible to air pollution (including acid rain), road salt, ice damage, and wind-throw. It often casts a dense shade that kills turf grass and other vegetation.

Range & Habitat: The native Sugar Maple is a common tree that occurs throughout Illinois (see Distribution Map); it probably occurs in every county. Habitats include rich mesic woodlands, sandy woodlands, wooded bluffs and hills, north-facing wooded slopes, wooded areas in protected coves and river valleys, lower slopes or bottoms of rocky ravines and canyons, and edges of limestone glades. Sugar Maple is often cultivated as a landscape tree in parks and yards. This tree is often the dominant canopy tree in mesic woodlands, or it can be codominant with American Beech or American Basswood. As a result of the suppression of wildfires and higher amounts of rainfall during the past several decades, it has displaced oaks, hickories, and other native trees in many woodlands around the state.

Faunal Associations: While honeybees and other bees sometimes collect pollen from the male flowers of Sugar Maple, cross-pollination is not achieved because they fail to visit the female flowers, which offer neither nectar nor pollen as a floral reward. The foliage, plant juices, and wood of Sugar Maple and other maples (Acer spp.) are sources of food to many insects. Chief among these feeders are the caterpillars of Dryocampa rubicunda (Rosy Maple Moth), Heterocampa biundata (Maple Prominent), and many other moths (see Moth Table). Another group of insect feeders include the larvae of Glycobius speciosus (Sugar Maple Borer), Xylotrechus aceris (Gall-Making Maple Borer), and other wood-boring beetles (see Wood-Boring Beetle Table). Many leafhoppers (mainly Eratoneura spp.) and aphids (Drepanaphis spp. & others) suck plant juices of maples; some of these species prefer Sugar Maple as a host plant (see Leafhopper & Aphid Table). Other insect feeders include plant bugs (Coccobaphes frontifer, Lygocoris hirticulus, Lygocoris vitticollis, & Plagiognathus flavipes), Neopulvinaria innumerabilis (Cottony Maple Scale), Phenacoccus acericola (Maple Mealybug), larvae of the sawfly Caulocampus acericaulis (Maple Petiole Borer), the larvae of Dasineura communis (Maple Gouty Vein Midge), and the wood-boring larvae of some horntails (Xiphydria abdominalis & Xiphydria maculata). After the protective bark has been damaged during the spring, some insects feed on the copious sap flow of Sugar Maple. These sap feeders include honeybees, some adult butterflies (Mourning Cloak, Comma, & Red Admiral), and many kinds of adult flies: Syrphid flies, Tachinid flies, flesh flies, blow flies, Muscid flies, skipper flies (Piophilidae), and the sap-feeding fly Aulacigaster leucopeza. Another small invertebrate species, Oligonychus aceris (Maple Spider Mite), feeds on the foliage. Vertebrate animals also use Sugar Maple and other maples as a source of food and protective cover. Some upland gamebirds and songbirds eat the buds or seeds (see Bird Table), while the Yellow-Bellied Sapsucker drills holes into the bark to feed on the sap. The Eastern Chipmunk, Fox Squirrel, Gray Squirrel, Red Squirrel, Southern Flying Squirrel, Meadow Vole, and White-Footed Mouse also eat the seeds of the samaras. White-Tailed Deer and Elk (the latter now extinct in the Midwest, except where it has been reintroduced) browse on the leaves and twigs, while the Beaver feeds on the wood. Because of heart rot, old maple trees provide dens for tree squirrels and such cavity-nesting birds as the Black-Capped Chickadee, Northern Flicker, Pileated Woodpecker, and Screech Owl. Other birds construct nests on branches of maple trees that vary in size (small saplings to mature trees).

Photographic Location:
The Arboretum of the University of Illinois in Urbana, Illinois.

Comments: Sugar Maple is a tree of economic importance because it is the source of maple syrup. The wood of Sugar Maple is also important economically because it is used in the construction of furniture, paneling, flooring, veneer, gunstocks, tool handles, cutting blocks, woodenware, sporting goods, bowling pins, and musical instruments. This tree is very similar to another species, Black Maple (Acer nigrum), which is sometimes regarded as a subspecies of Sugar Maple. Black Maple differs by having 3-lobed leaves with fewer teeth and slightly drooping margins, canescent leaf undersides, and trunk bark that is more furrowed. Black Maple is also native to Illinois, but it is less common. Trees displaying some evidence of hybridization between these two species are fairly common. Another tree that is often cultivated, the introduced Norway Maple (Acer platanoides), has leaves closely resembling those of Sugar Maple. Norway Maple differs by exuding a milky sap from the base of its petiole (when broken off from a branch), rather than a clear sap. It also has paired samaras that are more divergent (forming an angle that exceeds 120) and larger flowers in more erect clusters that are insect-pollinated.