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Acer rubrum, the red maple, also known as swamp maple, water maple, or soft maple, is one of the most common and widespread deciduous of eastern and central North America. The U.S. Forest Service recognizes it as the most abundant native tree in eastern North America. The red maple ranges from southeastern Manitoba around the Lake of the Woods on the border with Ontario and Minnesota, east to Newfoundland, south to Florida, and southwest to East Texas. Many of its features, especially its leaves, are quite variable in form. At maturity, it often attains a height around . 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 , on poor, dry , and almost anywhere in between. It grows well from sea level to about . 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 maple syrup production and for its medium to high quality lumber. It is also the state tree 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, , and Tsuga canadensis 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.
The leaf of the red maple offer the easiest way to distinguish it from its relatives. As with all North American maple trees, they are deciduous and arranged oppositely on the twig. They are typically long and wide with three to five with a serrated margin. The sinuses are typically narrow, but the leaves can exhibit considerable variation. 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 silver maple, A. saccharinum, are much more deeply lobed, more sharply toothed, and characteristically have five lobes. The upper side of A. rubrums leaf is light green and the underside is whitish and can be either glaucous or hairy. The leaf stalks are usually red and are up to 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 fall colors of red maple are most spectacular in the northern part of its range where climates are cooler.
The of the red maple are reddish in color and somewhat shiny with small . Dwarf shoots are present on many branches. The 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 are generally unisexual, with male and female flowers appearing in separate sessile clusters, though they are sometimes also bisexual. They appear in late winter to early spring, from December to May depending on elevation and latitude, usually before the leaves. The tree itself is considered polygamodioecious, meaning some individuals are male, some female, and some monoecious. Under the proper conditions, the tree can sometimes switch from male to female, male to hermaphroditic, and hermaphroditic to female. 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 calyx, usually at the twig tips. The staminate flowers are sessile. The pistillate flowers are borne on pedicels that grow out while the flowers are blooming, so that eventually the flowers are in a hanging cluster with stems long. The petals are lineal to oblong in shape and are pubescent. The pistillate flowers have one pistil formed from two fused carpels with a glabrous superior ovary and two long styles that protrude beyond the perianth. The staminate flowers contain between 4 and 12 , often with 8.
The fruit is a schizocarp of 2 samaras, each one long. Prior to dehiscence, the wings of the fruit are somewhat divergent at an angle of 50 to 60°. They are borne on long slender pedicels and are variable in color from light brown to reddish. 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.
In several other locations, the tree is absent from large areas but still present in a few specific habitats. An example is the Bluegrass region of Kentucky, where red maple is not found in the dominant open plains, but is present along streams. Unpublished manuscript. Here the red maple is not present in the bottom land forests of the Grain Belt, despite the fact it is common in similar habitats and species associations both to the north and south of this area. In the Northeastern US, red maple can be a climax forest species in certain locations, but will eventually give way to sugar maple.
A. rubrum does very well in a wide range of soil types, with varying textures, moisture, pH, and elevation, probably more so than any other forest tree in North America. A. rubrums wide pH tolerance means that it can grow in a variety of places, and it is widespread along the Eastern United States. It grows on glaciated as well as unglaciated soils derived from granite, gneiss, schist, sandstone, shale, slate, conglomerate, quartzite, and limestone. Chlorosis can occur on very alkaline soils, though otherwise its pH tolerance is quite high. Moist mineral soil is best for germination of seeds.
Red maple can grow in a variety of moist and dry biomes, from dry ridges and sunny, southwest-facing slopes to and . While many types of tree prefer a south- or north-facing aspect, the red maple does not appear to have a preference. Its ideal conditions are in moderately well-drained, moist sites at low or intermediate elevations. However, it is nonetheless common in mountainous areas on relatively dry ridges, as well as on both the south and west sides of upper slopes. Furthermore, it is common in swampy areas, along the banks of slow moving streams, as well as on poorly drained flats and depressions. In northern Michigan and New England, the tree is found on the tops of ridges, sandy or rocky upland and otherwise dry soils, as well as in nearly pure stands on moist soils and the edges of swamps. In the far south of its range, it is almost exclusively associated with swamps. Additionally, red maple is one of the most drought-tolerant species of maple in the Carolinas.Miller, J.H., & Miller, K.V. (1999). Forest plants of the southeast and their wildlife uses. Champaign, IL: Kings Time Printing.
Red maple is far more abundant today than when Europeans first arrived in North America. It only contributed minimally to old-growth upland forests, and would only form same-species stands in . The density of the tree in many of these areas has increased six- to seven-fold, and this trend seems to be continuing. One of the primary factors for this appears to be a loss of forest management that comes in several forms. First, a loss regular prescribed burns, such as those performed by Native Americans who would use the burns to enhance acorn and other seed harvesting. Second, continued heavy logging and a recent trend of young, shrubby forests recovering from past human disturbances. Third, the decline of American elm and American chestnut due to introduced diseases has contributed to its spread. Red maple dominates such sites, but largely disappears until it only has a sparse presence by the time a forest is mature. This species is in fact a vital part of forest regeneration in the same way that paper birch is.
Because it can grow on a variety of substrates, has a wide pH tolerance, and grows in both shade and sun, A. rubrum is a prolific seed producer and highly adaptable, often dominating disturbed sites. While many believe that it is replacing historically dominant tree species in the Eastern United States, such as , , , Tsuga and , red maple will only dominate young forests prone to natural or human disturbance. In areas disturbed by humans where the species thrives, it can reduce diversity, but in a mature forest, it is not a dominant species; it only has a sparse presence and adds to the diversity and ecological structure of a forest. Extensive use of red maple in landscaping has also contributed to the surge in the species' numbers as volunteer seedlings proliferate. Finally, disease epidemics have greatly reduced the population of elms and chestnuts in the forests of the US. While mainline forest trees continue to dominate mesic sites with rich soil, more marginal areas are increasingly being dominated by red maple.
A. rubrum is one of the first plants to flower in spring. A crop of seeds is generally produced every year with a bumper crop often occurring every second year. A single tree between in diameter can produce between 12,000 and 91,000 seeds in a season. A tree in diameter was shown to produce nearly a million seeds. Red maple produces one of the smallest seeds of any of the maples. Fertilization has also been shown to significantly increase the seed yield for up to two years after application.
The seeds are epigeal and tend to germinate in early summer soon after they are released, assuming a small amount of light, moisture, and sufficient temperatures are present. If the seeds are densely shaded, then germination commonly does not occur until the next spring. Most seedlings do not survive in closed forest canopy situations. However, one- to four-year-old seedlings are common under dense canopy. Though they eventually die if no light reaches them, they serve as a reservoir, waiting to fill any open area of the canopy above.
Trees growing in a Zone 9 or 10 area such as Florida will usually die from cold damage if transferred up north, for instance to Canada, Maine, Vermont, New Hampshire and New York, even if the southern trees were planted with northern red maples. Due to their wide range, genetically the trees have adapted to the climatic differences.
Red maple is able to increase its numbers significantly when associate trees are damaged by disease, cutting, or fire. One study found that 6 years after clearcutting a Oak-Hickory forest containing no red maples, the plot contained more than 2,200 red maple seedlings per hectare (900 per acre) taller than . One of its associates, the black cherry ( Prunus serotina), contains benzoic acid, which has been shown to be a potential allelopathic inhibitor of red maple growth. Red maple is one of the first species to start stem elongation. In one study, stem elongation was one-half completed in 1 week, after which growth slowed and was 90% completed within only 54 days. In good light and moisture conditions, the seedlings can grow in their first year and up to each year for the next few years, making it a fast grower.
The red maple is used as a food source by several forms of wildlife. Elk and white-tailed deer in particular use the current season's growth of red maple as an important source of winter food. Several Lepidoptera (butterflies and moths) utilize the leaves as food, including larvae of the rosy maple moth ( Dryocampa rubicunda); see List of Lepidoptera that feed on maples.
Due to A. rubrums very wide range, there is significant variation in hardiness, size, form, time of flushing, onset of dormancy, and other traits. Generally speaking, individuals from the north flush the earliest, have the most reddish fall color, set their buds the earliest and take the least winter injury. Seedlings are tallest in the north-central and east-central part of the range. In Florida, at the extreme south of the red maple's range, it is limited exclusively to swamplands. The fruits also vary geographically with northern individuals in areas with brief, frost-free periods producing fruits that are shorter and heavier than their southern counterparts. As a result of such variation, there is much genetic potential for breeding programs with a goal of producing red maples for cultivation. This is especially useful for making urban that require resistance from verticillium wilt, air pollution, and drought.
Red maple frequently hybridizes with silver maple; the hybrid, known as Freeman's maple, Acer × freemanii, is intermediate between the parents.
The following cultivars are completely male and are highly allergenic, with an OPALS allergy scale rating of 8 or higher: (2025). 9781607744917, Ten Speed Press. ISBN 9781607744917
The following cultivars have an OPALS allergy scale rating of 3 or lower; they are completely female trees, and have low potential for causing allergies:
Red maple is a good choice of a tree for urban areas when there is ample room for its root system. Forming an association with arbuscular mycorrhizal fungi can help A. rubrum grow along city streets. It is more tolerant of pollution and road salt than sugar maples, although the tree's fall foliage is not as vibrant in this environment. Like several other maples, its low root system can be invasive and it makes a poor choice for plantings near paving. It attracts squirrels, who eat its buds in the early spring, although squirrels prefer the larger buds of the silver maple.
Red maples make vibrant and colorful bonsai, and have year around attractive features for display.
Red maple is also used for the production of maple syrup, though the hard maples Acer saccharum (sugar maple) and Acer nigrum (black maple) are more commonly utilized. One study compared the sap and syrup from the sugar maple with those of the red maple, as well as those of the Acer saccharinum (silver maple), Acer negundo (boxelder), and Acer platanoides (Norway maple), and all were found to be equal in sweetness, flavor, and quality. However, the buds of red maple and other soft maples emerge much earlier in the spring than the sugar maple, and after sprouting chemical makeup of the sap changes, imparting an undesirable flavor to the syrup. This being the case, red maple can only be tapped for syrup before the buds emerge, making the season very short.
Native Americans used red maple bark as a wash for inflamed eyes and cataracts, and as a remedy for hives and muscular aches. They also would brew tea from the inner bark to treat coughs and diarrhea. Pioneers made cinnamon-brown and black dyes from a bark extract, and iron sulphate could be added to the tannin from red maple bark in order to make ink.
Red maple is a medium quality firewood, possessing less heat energy, nominally , than other hardwoods such as ash: , oak: , or birch: .
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