Maples
Maples
The maples are about 150 species of angiosperm trees and shrubs in the genus Acer, family Aceraceae. Most maples occur in temperate forests of the Northern Hemisphere.
Maples are characterized by the shape of their leaves, which in most species are broadly palmate with a three- or five-lobed outline, and are arranged in an opposite fashion on their branches. Maples have seasonally deciduous foliage, which is shed in the autumn. The leaves of many species of maples develop beautiful yellow, orange, or red colors in the autumn, prior to shedding for the winter. Maple flowers appear early in the springtime, and consist of nonshowy, rather inconspicuous inflorescences. The flowers of some species produce nectar and are insect pollinated, while others shed their pollen into the air and are wind pollinated. Maples have distinctive winged seeds known as samaras, which are arranged in opposite pairs.
Maples of North America
About twelve tree-sized species of maples grow naturally in North America, along with other shrub-sized species. Other nonnative species of maples have been widely introduced to North America as attractive, ornamental plants.
The most widespread native species is sugar or rock maple (Acer saccharum ), a prominent tree in temperate forests of eastern Canada and the northeastern United States. Sugar maple is extremely tolerant of shade and is a major component of mature and older-growth angiosperm forests on rich, well-drained sites within its range. Sugar maple grows as tall as 115 feet (35 m), can achieve a diameter of more than 3 ft (1 m), and can live to be older than four centuries. The roughly five-lobed leaves of sugar maple turn a beautiful, orange-yellow color in the autumn, when the green color of chlorophyll fades, exposing the yellow and orange pigments in the leaves. Sugar maple is the national tree of Canada, and a stylized leaf of this species is featured prominently on the Canadian flag. This species was subject to a widespread decline and dieback over parts of its range during the 1980s, but has since apparently recovered.
Black maple (A. nigrum ) is rather similar in appearance to sugar maple, but its leaves have a more three-lobed appearance. Florida maple (A. barbatum ) replaces the sugar maple in southeastern North America.
Red maple (A. rubrum ) is another widely distributed species, occurring over much of eastern North America, from northern Ontario to southern Florida. Its habitat is highly varied, ranging from flooded swamps to dry hills and rocky slopes. The foliage of this species turns a brilliant scarlet in the autumn. The natural distribution of the silver maple (A. saccharinum ) is largely restricted to swamps and floodplains.
There are fewer species of maples in western North America. The bigleaf maple (A. macrophyllum ) has leaves that can be 12 inches (30 cm) in diameter, turning a yellow-brown in the autumn. Vine maple (A. circinatum ) has scarlet leaves in the fall.
The box elder or Manitoba maple (A. negundo ) is the only species of maple that has a compound leaf, consisting of three to seven leaflets. This fast-growing species is common in moist sites near water, and is an urban weed in many areas.
Lumber from maples
Some maple species have a hard, durable wood that can be used to make furniture, cabinets, interior trim, hardwood flooring, and other products that require strength and an ability to take a smooth finish. In North America, sugar and black maples are most commonly used for these purposes, and are known to carpenters as “hard” maples. Unusual and attractive grains known as curly and bird’s-eye are especially desirable for the making of furniture. Lumber is also made from red, silver, and bigleaf maples, but the wood of these “soft” maples is not considered to be of as high a quality.
Various species of maples are grown as horticultural plants in urban areas, in parks, around homes, and along country roads. Sugar, black, and silver maples are native species commonly grown along rural and urban roadsides. Some nonnative species of maples are also commonly used in horticulture, especially Norway maple (Acer platanoides ), sycamore maple (A. pseudo-platanus ), English maple (A. campestre ), and Japanese maple (A. palmatum ).
Maple syrup
In the early spring, when there is still snow on the ground, various species of temperate angiosperm trees transport large quantities of sap from their roots to their branches, where energy is needed to develop the
KEY TERMS
Fall coloration —In the late fall, the leaves of seasonally deciduous trees stop synthesizing the green photosynthetic pigment known as chlorophyll. The reduced concentrations of this dominant pigment unmask other, secondary pigments, which are yellow, orange, red, or brown in color. Depending on the tree species, the autumn foliage may develop spectacular displays of these secondary colors prior to leaf-drop.
Palmate —Refers to a leaf shape in which the lobes or veins appear to radiate from one central point, as is typical of the foliage of maples.
Samara —A dry, winged seed, that does not split open when ripe. The samaras of maples are arranged in opposite pairs, and when they are shed they helicopter away from the parent tree to achieve a short-distance dispersal.
new season’s crop of twigs, flowers, and leaves. The flow in sugar and black maples is especially voluminous, and these species are widely tapped for their sweet sap, which typically contains about 6% sucrose. Maple sap is commonly collected by drilling holes into the base of the tree, inserting a tap, and collecting the drippings in small pails. More recently, low-head suction systems have been developed, in which sap is collected from large numbers of tapped trees, using a system of interconnected hoses that drain to a central location. After the sap is collected, it is condensed by evaporation, often using wood-stoked fires and large, flat boiling pans. Alternatively, it may be condensed using machines that work by reverse osmosis.
The final product is usually maple syrup—about 10.5 gallons (40 l) of raw sap is required to make 1 quart (1 l) of maple syrup. Sometimes, the syrup is further evaporated to produce maple sugar. The syrup grade and its value is determined by color. A light amber syrup is more desirable than one that has been rendered a darker brown by high-temperature caramelization. Syrups with a delicate flavor are also considered to be of better quality than those with a more pronounced flavor.
Maple sugaring is especially common in rural areas of southeastern Canada and New England. Many urban people in those regions love to go out into the country to participate in sugar-maple festivals, considered an indispensable rite of spring.
Resources
BOOKS
Judd, Walter S., Christopher Campbell, Elizabeth A. Kellogg, Michael J. Donoghue, and Peter Stevens. Plant Systematics: A Phylogenetic Approach. 2nd ed. with CD-ROM. Suderland, MD: Sinauer, 2002.
OTHER
MapleTrees.com. “Maple Trees” <http://maple-trees.com> (accessed December 3, 2006).
University of Maine Cooperative Extension. “How to Tap Maple Trees and Make Maple Syrup” <http://www.umext.maine.edu/onlinepubs/PDFpubs/7036.pdf> (accessed December 3, 2006).
Bill Freedman