Acer rubrum, the red maple, also known as swamp maple, water maple, or soft maple, is one of the most common and widespread deciduous听听of eastern and central North America. The听听recognizes it as the most abundant native tree in eastern North America.听The red maple ranges from southeastern听听around the听听on the border with听听and听, east to听, south to听, and southwest to听. Many of its features, especially its leaves, are quite variable in form. At maturity, it often attains a height around 30听m (100听ft). Its flowers, petioles, twigs, and seeds are all red to varying degrees. Among these features, however, it is best known for its brilliant deep scarlet foliage in autumn.
Over most of its range, red maple is adaptable to a very wide range of site conditions, perhaps more so than any other tree in eastern North America. It can be found growing in听, on poor, dry听, and almost anywhere in between. It grows well from听听to about 900听m (3,000听ft). Due to its attractive fall foliage and pleasing form, it is often used as a shade tree for landscapes. It is used commercially on a small scale for听听production and for its medium to high quality lumber. It is also the听听of Rhode Island. The red maple can be considered weedy or even invasive in young, highly disturbed forests, especially frequently logged forests. In a mature or old-growth northern hardwood forest, red maple only has a sparse presence, while shade-tolerant trees such as sugar maples,听, and听听thrive. By removing red maple from a young forest recovering from disturbance, the natural cycle of forest regeneration is altered, changing the diversity of the forest for centuries to come.
DESCRIPTION
Though A. rubrum听is sometimes easy to identify, it is highly changeable in morphological characteristics. It is a medium to large sized tree, reaching heights of 27 to 38听m (90 to 120听ft) and exceptionally over 41听m (135听ft) in the southern Appalachians where conditions favor its growth. The leaves are usually听9 to 11听cm (3+1鈦�2听to听4+1鈦�4听in) long on a full-grown tree. The trunk diameter often ranges from 46 to 88听cm (18 to 35听in); depending on the growing conditions, however, open-grown trees can attain diameters of up to 153听cm (60听in). The trunk remains free of branches until some distance up the tree on forest grown trees, while individuals grown in the open are shorter and thicker with a more rounded crown. Trees on poorer sites often become malformed and scraggly.听Generally the crown is irregularly ovoid with ascending whip-like curved shoots. The听听is a pale grey and smooth when the individual is young. As the tree grows the bark becomes darker and cracks into slightly raised long plates.听The largest known living red maple is located near听, at a height of 38.1听m (125听ft) and a bole circumference, at breast height, of 4.95听m (16听ft 3听in).
The听听of the red maple offer the easiest way to distinguish it from its relatives. As with all North American maple trees, they are听听and arranged oppositely on the twig. They are typically 5鈥�10听cm (2鈥�4听in) long and wide with three to five听听with a serrated margin. The听听are typically narrow, but the leaves can exhibit considerable variation.听When five lobes are present, the three at the terminal end are larger than the other two near the base. In contrast, the leaves of the related听,听A. saccharinum, are much more deeply lobed, more sharply toothed, and characteristically have five lobes. The upper side of听A. rubrum's leaf is light green and the underside is whitish and can be either听听or hairy. The leaf stalks are usually red and are up to 10听cm (4听in) long. The leaves can turn a characteristic brilliant red in autumn, but can also become yellow or orange on some individuals. Soil acidity can influence the color of the foliage and trees with female flowers are more likely to produce orange coloration while male trees produce red. The听听of red maple are most spectacular in the northern part of its range where climates are cooler.
The听听of the red maple are reddish in color and somewhat shiny with small听. Dwarf shoots are present on many branches. The听听are usually blunt and greenish to reddish in color, generally with several loose scales. The lateral buds are slightly stalked, and in addition, collateral buds may be present, as well. The buds form in fall and winter and are often visible from a distance due to their large size and reddish tint. The leaf scars on the twig are V-shaped and contain three bundle scars.
The听听are generally unisexual, with male and female flowers appearing in separate听听clusters, though they are sometimes also bisexual. They appear in late winter to early spring, from December听to May depending on elevation and latitude, usually before the leaves. The tree itself is considered听, meaning some individuals are male, some female, and some听.听Under the proper conditions, the tree can sometimes switch from male to female, male to hermaphroditic, and hermaphroditic to female.听The red maple will begin blooming when it is about 8 years old, but it significantly varies between tree to tree: some trees may begin flowering when they are 4 years old. The flowers are red with 5 small petals and a 5-lobed听, usually at the twig tips. The staminate flowers are听. The pistillate flowers are borne on听听that grow out while the flowers are blooming, so that eventually the flowers are in a hanging cluster with stems听1 to 5听cm (1鈦�2听to 2听in) long.听The petals are lineal to oblong in shape and are pubescent. The pistillate flowers have one听听formed from two fused carpels with a glabrous superior ovary and two long听听that protrude beyond the听. The staminate flowers contain between 4 and 12听, often with 8.
The听听is a听听of 2听, each one听15 to 25听mm (5鈦�8听to 1听in) long. Prior to dehiscence, the wings of the fruit are somewhat divergent at an angle of 50 to 60掳. They are borne on long slender pedicels and are variable in color from light brown to reddish.听They ripen from April through early June, before even the leaf development is altogether complete. After they reach maturity, the seeds are dispersed for a 1- to 2-week period from April through July.
