Acer ( ) is a genus of trees or shrubs commonly known as Maple.

Maples are variously classified in a family of their own, the Aceraceae, or together with the Hippocastanaceae included in the family Sapindaceae. Modern classifications, including the Angiosperm Phylogeny Group system, favour inclusion in Sapindaceae. The type species of the genus is Acer pseudoplatanus (Sycamore Maple).

There are approximately 125 species, most of which are native to Asia, , with a number also appearing in Europe, northern Africa, and North America.

The word Acer is derived from a Latin word meaning "sharp", referring to the characteristic points on maple leaves. It was first applied to the genus by the French botanist Joseph Pitton de Tournefort in 1700.A red maple leaf is the prominent feature of the flag of Canada.

Morphology

Maples are mostly trees growing to 10-45 meters (30-145 ft) in height. Others are shrubs less than 10 meters tall with a number of small trunks originating at ground level. Most species are deciduous, but a few in southern Asia and the Mediterranean region are evergreen. Most are shade-tolerant when young, and are often late-successional in ecology; many of the root systems are typically dense and fibrous. A few species, notably Acer cappadocicum, frequently produce root sprouts, which can develop into clonal colonies.

Maples are distinguished by opposite leaf arrangement. The leaves in most species are palmate veined and lobed, with 3-9 (rarely to 13) veins each leading to a lobe, one of which is central or apical. A small number of species differ in having palmate compound, pinnate compound, pinnate veined or unlobed leaves. Several species, including Acer griseum (Paperbark Maple), Acer mandshuricum (Manchurian Maple), Acer maximowiczianum (Nikko Maple), and Acer triflorum (Three-flowered Maple), have trifoliate leaves. One species, Acer negundo (Box-elder), has pinnately compound leaves that may be simply trifoliate or may have five, seven, or rarely nine leaflets. A few, such as Acer laevigatum (Nepal Maple) and Acer carpinifolium (Hornbeam Maple), have pinnately-veined simple leaves.

The flowers are regular, pentamerous, and borne in racemes, corymbs, or umbels. They have four or five sepals, four or five petals about 1–6 mm long (absent in some species), four to ten stamens about 6-10 mm long, and two pistils or a pistil with two styles. The ovary is superior and has two carpels, whose wings elongate the flowers, making it easy to tell which flowers are female. Maples flower in late winter or early spring, in most species with or just after the leaves appear, but in some before them.

Maple flowers are green, yellow, orange or red. Though individually small, the effect of an entire tree in flower can be striking in several species. Some maples are an early spring source of pollen and nectar for bees.

The distinctive fruit are called samaras or "maple keys". These seeds, or 'whirlybirds,' occur in distinctive pairs each containing one seed enclosed in a "nutlet" attached to a flattened wing of fibrous, papery tissue. They are shaped to spin as they fall and to carry the seeds a considerable distance on the wind. Children often call them "helicopters" due to the way that they spin as they fall. Seed maturation is usually in a few weeks to six months after flowering, with seed dispersal shortly after maturity. However, one tree can release hundreds of the seeds at a time. Depending on the species, the seeds can be small and green to orange and big with thicker seed pods. The green seeds are released in pairs, sometimes with the stems still connected. The yellow seeds are released individually and almost always without the stems. Most species require stratification in order to germinate, and some seeds can remain dormant in the soil for several years before germinating.

The genus is subdivided by its morphology into a multitude of sections and subsections.

Pests and diseases

The leaves are used as a food plant for the larvae of a number of Lepidoptera species (see List of Lepidoptera that feed on maples). Aphids are also very common sap-feeders on maples. In horticultural applications a dimethoate spray will solve this.

Maples are affected by a number of fungal diseases. Several are susceptible to Verticillium wilt caused by Verticillium species, which can cause significant local mortality. Sooty bark disease, caused by Cryptostroma species, can kill trees which are under stress due to drought. Death of maples can rarely be caused by Phytophthora root rot and Ganoderma root decay. Maple leaves in late summer and autumn are commonly disfigured by "tar spot" caused by Rhytisma species and mildew caused by Uncinula species, though these diseases do not usually have an adverse effect on the trees' long-term health.

Uses

Horticulture

Maples are planted as ornamental trees by homeowners, businesses and municipalities. Acer platanoides (Norway Maple) is especially popular as it is fast-growing and extremely cold-resistant, though it is also an invasive species in some regions. Other maples, especially smaller or more unusual species, are popular as specimen trees.

Cultivars

Numerous maple cultivars which have been selected for particular characteristics can be propagated only by asexual reproduction such as cuttings, tissue culture, budding or grafting. Acer palmatum (Japanese Maple) alone has over 1,000 cultivars, most selected in Japan, and many of them no longer propagated or not in cultivation in the western world. Some delicate cultivars are usually grown in pots and rarely reach heights of more than 50-100 cm. Maple is also a key wood in the construction of percussion instruments like drum kits. Some of the best drum building companies like DW (Drum Workshop) use maple extensively throughout their mid-pro range.

Bonsai

are a popular choice for the art of bonsai. Acer palmatum (Japanese Maple), Acer buergerianum (Trident Maple), Acer ginnala (Amur Maple), Acer campestre (Field Maple) and Montpellier Maple (A. monspessulanum) are popular choices and respond well to techniques that encourage leaf reduction and ramification, but most species can be used.

Collections

Maple collections, sometimes called aceretums, occupy space in many gardens and arboreta around the world including the "five great W's" in England: Wakehurst Place Garden, Westonbirt Arboretum, Windsor Great Park, Winkworth Arboretum and Wisley Garden. In the United States, the aceretum at the Harvard-owned Arnold Arboretum in Boston is especially notable. In the number of species and cultivars, the Esveld Aceretum in Boskoop, Netherlands is the largest in the world.

Tourism

Many maples have bright autumn foliage, and many countries have leaf-watching traditions. In Japan, the custom of viewing the changing colour of maples in the autumn is called "momijigari". Nikko and Kyoto are particularly favoured destinations for this activity. In addition, in Korea, the same viewing activity is called "Danpung-Nori" and Seoraksan and Naejang-san mountains are very famous places for it.

The particularly spectacular fall colours of the Acer saccharum (Sugar Maple) are a major contributor to the seasonal landscape in southeastern Canada and in New England. Fall tourism is a boon to the economy of this region, especially in Quebec, Vermont, New Hampshire and Western Massachusetts. In the American Pacific Northwest and British Columbia it is the spectacular fall colours of Acer circinatum (Vine Maple) that draw tourists and photographers.

Commercial uses

Maples are important as source of syrup and wood. Dried wood is often used for the smoking of food. They are also cultivated as ornamental plants and have benefits for tourism and agriculture.

Maple syrup

The Sugar Maple (Acer saccharum) is tapped for sap, which is then boiled to produce maple syrup or made into maple sugar or maple taffy. It takes about 40 liters of Sugar Maple sap to make a liter of syrup. Syrup can be made from closely-related species as well, but their output is inferior.

Food

The seeds are sometimes consumed after they are boiled in water to remove bitter tasting compounds.

Timber

Some of the larger maple species have valuable timber, particularly Sugar Maple in North America, and Sycamore Maple in Europe. Sugar Maple wood, often known as "hard maple", is the wood of choice for bowling pins, bowling alley lanes, pool cue shafts, and butcher's block. Maple wood is also used for the production of wooden baseball bats, though less often than ash or hickory due to the tendency of maple bats to shatter when broken.

Some maple wood has a highly decorative wood grain, known as flame maple and quilt maple. This condition occurs randomly in individual trees of several species, and often cannot be detected until the wood has been sawn, though it is sometimes visible in the standing tree as a rippled pattern in the bark. Birdseye maple is another distinctive grain pattern.

Tonewood

Maple is considered a tonewood, or a wood that carries sound waves well, and is used in numerous musical instruments. Maple is harder and has a brighter sound than Mahogany, which is the other major tonewood used in instrument manufacture.

Most drums are made from maple. From the 70s to the 90s, maple drum kits were a vast majority of all drum kits made. In recent years, Birch has become popular for drums once again. Electric guitar necks are commonly made from maple. The necks of the Fender Stratocaster and Telecaster were originally an entirely maple one piece neck, but later were also available with rosewood fingerboards. Maple fingerboards have a brighter sound than rosewood.The tops of Gibson's Les Paul guitars are made from carved maple. Many Les Pauls have quilted or flamed maple tops, and these models are particularly prized by players and collectors. Very few solid body guitars are made entirely from maple, as it is considered too heavy. Many guitars do, however, have maple tops or veneers. Gibson uses laminated maple in the manufacture of many of its semi-hollowbody guitars. The back and sides of most violins are made from maple.

Maple is also used to make bassoons and double basses.

Agriculture

As they are a major source of pollen in early spring before many other plants have flowered, maples are important to the survival of honeybees that play a commercially-important role later in the spring and summer.

Gallery

Image:Acer cappadocicum spring.jpg|Acer cappadocicum (Cappadocian Maple)Image:Acer carpinifolium.jpg|Acer carpinifolium leavesImage:Paperbark Maple Acer griseum Leaves Closeup 2856px.jpg|Acer griseum compound (trifoliate) leafImage:BigleafMaple 0304.jpg|Acer macrophyllum flowers and young leavesImage:Acer laevigatum 3.jpg|Acer laevigatum leaves and fruitImage:Acer sempervirens leaves.jpg|Acer sempervirens foliageImage:Acer ginnala.jpg|Acer ginnala foliageImage:redmaple.jpg|Acer rubrum trees in autumnImage:TenryujiMomiji.jpg|Acer palmatum trees and bamboo in JapanImage:Bi-colored Maple Tree.jpg|Acer grandidentatum in autumn colourImage:Maple leaf Fcb981.JPG|Acer platanoides leafImage:Red maple leaf.jpg|Acer palmatum leaf in autumn

References

1. Sunset Western Garden Book, 1995:606–607
2. van Gelderen, C. J. & van Gelderen, D. M. (1999). Maples for Gardens: A Color Encyclopedia
3. Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan ISBN 0-333-47494-5.
4. Classification of maples
5. Phillips, D. H. & Burdekin, D. A. (1992). Diseases of Forest and Ornamental Trees. Macmillan. ISBN 0-333-49493-8.