Maples are trees or shrubs of the genus Acer. They are variously classified in a family of their own, the Aceraceae, or (together with the Hippocastanaceae) included in the Sapindaceae. This is a debate of very long standing, and APG favours a wide circumscription, as a matter of style.
Maples are distinguished by opposite leaf arrangement. The leaves are usually palmately lobed, although palmate compound, pinnate compound, pinnate veined or unlobed shapes occur. The flowers are regular, pentamerous, and borne in racemes, corymbs, or umbels. Their distinctive fruits occur in pairs, called keys, shaped to spin as they fall and carry the seeds a considerable distance on the wind (see samara). The derivation of the name "acer" is uncertain, as it is a very old name. One of the options is that derives from the Latin acris (sharp), from the hardness of the wood, supposedly used for spears in the past.
The leaves in most species are palmately veined and lobed, with 3-9 veins each leading to a lobe, one of which is in the middle. Several species, including the Paperbark Maple Acer griseum, Manchurian Maple Acer mandshuricum, Nikko Maple Acer maximowicziana, and Three-flower Maple Acer triflorum, have trifoliate leaves. The Manitoba Maple (Acer negundo) has pinnately compound leaves that may be simply trifoliate or may have 5, 7, or rarely 9 leaflets. One maple, the Hornbeam Maple Acer carpinifolium, has pinnately-veined simple leaves that resemble those of hornbeams.
Maples flower in late winter or early spring, in some species before the leaves appear, but with or just after the leaves in most. Their flowers are small and inconspicuous, though the effect of an entire avenue of maples in flower can be striking. They have five sepals, five petals about 1-6 mm long, twelve stamens about 6-10 mm long in two rings of six, 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. Within a few weeks to six months of flowering, the trees drop large numbers of seeds.
Maples are important as cultivated ornamental plants, for syrup sources and timber production. Some species have bright autumnal leaf coloring. The Sugar Maple (Acer saccharum) is tapped for sap, which is then boiled to produce maple syrup or made into maple sugar or maple candy. Quebec is the world's largest producer of maple sugar products. The hard maple that is the wood of choice for bowling pins and bowling alley lanes is yielded by Sugar Maple.
Maples are an important early spring source of pollen and nectar for bees, especially honeybees, which use its resources for spring buildup. Maples are used as a food plant for the larvae of a number of Lepidoptera species (see List of Lepidoptera which feed on Maples).
The flag of Canada depicts a stylized maple leaf and is a prominent national symbol.
Photo attribution: Maple photo used by permission of David Beaulieu at www.landscaping.about.com
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