Of the family Aceraceae, this well-known group of trees contains 125 species worldwide, mostly found in the temperate regions of East Asia. Of these species approximately 12 are native to North America, and are found in a wide variety of habitats, except the very cold and very dry. Seven of these species are trees at maturity, two are shrub-like in character, and the rest vary depending on local conditions. Huge and robust to decidedly small and delicate and from drab autumnal drapery to breathtakingly colourful displays, maples have a variety of visual representations. Considered one of the harder woods, these trees vary in their responses to pollution and environmental circumstances, from extremely adaptable to finicky in their growth. The common characteristics of this species are found in the subtleties of the trees development. Structurally, the iconic leaves and buds are borne in pairs along the stem. Branches also tend to be paired, although disparate in strength. The flowers are generally inconspicuous, opening in spring and are followed by distinctive winged fruit, which are commonly called keys. The leaves are often palmately lobed in the recognizable shape of an open palm, with three or five being the most common number. An example of exception to the rule, is the Boxelder with as many as nine lobes. All maples are shallow and fibrous rooted. This often presents difficulties in landscape applications as little can grow beneath them. The roots, in their search for water, also tend to clog drainage tile and sewers. There are 12 recognized species of maple, most of them native to central and east Asia, with a few in Europe, northern Africa and North America. One type of maple, native to the Southern Hemisphere, is the poorly studied Acer laurinum, which is found on some islands in Indonesia. While it does not have the traditionally lobed leaves of most maples, it does maintain the distinct leaf and branch pairing. Of the species found in Asia, the Amur Maple has the most extensive habitat. Native to Korea, Japan, Mongolia, and Siberia it grows to a maximum height of 20 ft and is more commonly referred to as the Siberian Maple. Of comparable stature, the Japanese Maple has similar distribution throughout Asia, although not as far north as the Amur, and is native to China, Korea, and Japan. The two species with the smallest native habitat are both found in eastern Asia, the Vine Leaf Maple of Japan and the Paperbark Maple, native to central China. Both of these can reach heights of 30 ft, although generally stay on the smaller side. Moving across western Asia and into Europe, native territories start to expand. Extending from southwestern Asia and into Europe the Hedge, or Field Maple as it is commonly called, can be found and grows between 25 and 35 ft tall. Below are the species native to North America and their distinguishing characteristics.
Acer glabrum Rock Maple, Douglas Maple, Rocky Mountain Maple
This generally small tree with short trunk and irregular crown is native to the northern Rockies and coastal mountains of the Pacific Northwest. Fond of moist growing conditions it is found primarily along streams and rivers, often reaching approx 30 ft (10 m) in height. It is valued as an ornamental among arborists for its reddish fall display.
Acer macrophyllum Oregon Maple, Bigleaf Maple, Broadleaf Maple
The most common maple in North America, this species prefers gravelly, moist soil and is found along the Pacific coast from California to southern British Columbia. As pseudonyms suggest, very large leaves distinguish the Oregon Maple, usually 12 inches (30cm) in width and almost as long. On vigorous branches and young trees, they will reach up to 24 inches (60cm). The largest and longest living native maple, it can reach heights of 100ft (30m) during its 250 year lifespan. This species is moderately shade-tolerant in forested conditions, tending to form a straight trunk for at least half its height, with a narrow crown. In more open conditions it will grow a shorter trunk and a broad, rounded crown. Generally it's not grown ornamentally unless in large-scale installations.
Acer negundo Box Elder, Manitoba Maple, Ash-leaf Maple
Fast-growing, weak-wooded, and often considered an invasive species this tree is easily able to establish itself in most conditions. Native to lakeshores and stream banks, with a preference for seasonally flooded and disturbed sites, it exploits exposure to full sun and quickly takes root. Within the two centuries since colonization it has expanded its already wide distribution from throughout the eastern United States, across the Great Plains in both the US and Canada, even into California. It is now in nearly every corner of the continent, taking its particular liking for disturbed sites, and now flourishing amidst urban decay. Its tolerance for abused and deteriorated soils, make its otherwise invasive tendencies quite useful. Used in shelter-belts and street planting, this species will quickly grow to 70ft (21m) high, with a generally short trunk and a broad uneven crown of crooked limbs and branches. As with most fast-growing, weak-wooded trees, it is short-lived at about 65yrs. Unique for having a variably, pinnately divided leaf it will have up to seven and sometimes nine leaflets per leaf on developing trees. The seeds are extraordinarily viable and will germinate in the spring. Syrup can be distilled from its sap, similar to the Sugar Maple, however it is considered inferior in quality.
Acer pensylvanicum Striped Maple, Snakebark Maple, Moose Maple
A small tree of northern woods, this maple is found in forests from Ontario and Nova Scotia to Wisconsin, Ohio and New Jersey. Reaching heights and breadths of approx 30 ft (9 m) in the understory where preferred soil conditions are cool, moist, well drained and quite acidic. In cultivation this tree usually reaches 20 ft (6 m) under similar soil conditions. It can however, be badly scorched by the sun, especially in dry soil. The twigs are a favored food of moose and deer, and trees are often established by game wardens to provide browse in winter. The inner bark was traditionally used by Native peoples for medicinal purposes, from an emetic to a gargle for sore throats.
Acer rubrum Red Maple, Swamp Maple, Soft Maple
Known to have the most extensive natural range of any deciduous tree in eastern North America, the habitat of this maple is found from the Florida everglades to the mixed forests around Lake Superior. In native habitats, consisting of cool, most, acidic soil adjacent to swamps and marshes it can reach heights of 80 ft (25 m) and lives on average to 130 years. It can be tolerant of other soils, if they are not alkaline or compacted, however they will generally not grow as large. The crown tends to be narrow and high when in the forest, lower and more rounded when open grown. This maple does not perform well in dry or polluted environs, or close to roads, where salt spray occurs from traffic in winter. It has scarlet flowers, which open in very late winter or early spring. These mature into keys, also crimson in colour, until they are shed in mid-June, when they are dry and tan in colour. Leaves are usually three-lobed with fine teeth around the edges and ranging in colour from silvery to mid-green.
Acer saccharinum Silver Maple, Soft Maple
A rapid-growing tree of eastern North America, this maple reaches heights in excess of 100 ft. (30 m) during its 100-year lifespan. In forest conditions the crown is high and open, as with other species grown in the open the trunk is shorter, developing into a number of outward-arching limbs. Its preferred setting is moist, rich bottomlands near water. It is adaptable to other soils, however may not thrive in shade and alkaline conditions. While fairly tolerant of urban conditions, planted as a street tree the roots can clog drainage tile and sewers. Weak-wooded and prone to rot, it tends to drop branches in storms. The deeply five-lobed leaves are coarsely toothed and while it is closely related to the red maple they generally turn pale yellow-green or brownish before dropping in autumn. Flowers appear in late February to early April, individually small but tend to cluster, producing keys in vast numbers that drop in mid-June.
Acer saccharum Sugar Maple
If only for its glorious autumnal display, the Sugar Maple is one of the more notable trees of North America. Greatly prized for maple syrup as well as its timber, this is one of the more prevalent forest trees, often found in extensive pure strands. Some authorities recognize Black Maple (A. nigrum), Big-Toothed Maple (A. grandidentatum), Florida Maple (A. barbatum), and Chalk Maple (A. leucoderme) as subspecies, while others treat these as separate species, differing in range, ecological preference, autumnal display, and minor characteristics. In forest settings it can reach 120 ft. (35 m) and live from 300 to 400 years. However in cultivation, as lifespan is often shortened, the maximum size is about 70 ft. (20 m). The trunk develops into one to three major ascending limbs. Immediately following the small, clustered, yellow-green flowers, leaves emerge in May quickly expanding into the classic five-lobed maple-leaf shape. Foliage is often confused with the introduced Norway Maple, which produces a milky sap when the leaf-stem is broken. Keys ripen in late summer and early autumn, with an easily identifiable rounded green body. This tree prefers moist, well-drained, fertile, and slightly acid soils laid over limestone bedrock. In cultivation these same preferences apply, and while there is some tolerance of neutral or slightly alkaline soils it has a high susceptibility to damage from air and water-borne pollutants. This species performs especially well in the company of other trees. Maple lumber is broadly classified into two groups, hard maples and soft maples. While they are all technically hardwoods this classification is in response to general the characteristics and woodworking properties of the tree. Hard maples include the Sugar Maple and Black Maple, the majority of which are harvested in the Middle Atlantic and Great Lake States. This type of wood is heavy, durable, and resistant to shock. A large portion of this lumber is used for flooring, furniture, butchers blocks, and musical instruments. This wood is easy to use and durable. Types which are considered soft maples include Silver Maple, Red Maple, Boxelder, and the Bigleaf Maple. While not as heavy and strong as the hard maple this wood is still durable and is used in a number of applications from railroad cross ties to furniture.