Leaves of Plants

Leaf is the main food-making part of almost all plants. Garden flowers, grasses, shrubs, and trees depend on their leaves to make food for the rest of the plant. So do many other plants, including ferns, vegetables, vines, and weeds. Each leaf is a little food factory. It captures energy from sunlight and uses it to make sugar out of water from the soil and carbon dioxide, a gas in the air. This sugar is changed to many other chemical substances.

These substances become the food that provides plants with energy to grow, to produce flowers and seeds, and to carry on all their other activities. Plants store the food made by leaves in their fruits, roots, seeds, stems, and even in the leaves themselves. Without this food, plants could not live. In addition, all the food that people and animals eat comes either from plants or from animals that eat plants.Leaves vary in appearance among plants. Many are oval, but others are shaped like arrowheads, feathers, hands, hearts, or any number of other objects.

However, most leaves can be divided into three groups according to their basic shape. (1) Broad leaves are the type of leaf that most plants have. These leaves are fairly wide and flat. Plants that have such leaves include maple and oak trees, pea plants, and rosebushes. (2) Narrow leaves are long and slender. Narrow leaves grow on grasses. Grasses include not only lawn grasses but also barley, corn, oats, wheat, and other cereal grasses. Lilies, onions, and certain other plants also have narrow leaves. (3) Needle leaves grow on firs, pines, spruces, and most other cone-bearing trees and shrubs. Needle leaves resemble short, thick sewing needles. A few other kinds of cone-bearing plants, including certain cedars and junipers, have scalelike leaves.

Most leaves grow from 1 to 12 inches (2.5 to 30 centimeters) in length. Some plants, however, have huge leaves. The largest leaves grow on the African raffia palm. The leaves of this tree measure up to 65 feet (20 meters) long. The giant water lily of South America has round, floating leaves that grow up to 6 feet (1.8 meters) across. In contrast, some plants have extremely small leaves. The true leaves of asparagus plants, for example, are so tiny that they are hard to see without a magnifying glass. In these plants, the stems, rather than the leaves, produce food.

The number of leaves on plants ranges from several to thousands. Most soft-stemmed plants have few leaves. For instance, a barley or wheat plant produces only 8 to 10 leaves each season. But trees and shrubs have an enormous number of leaves. A fully grown elm or pine tree produces thousands of leaves. Some simple plants that manufacture their own food do not have leaves. For example, liverworts and mosses are simple food-making plants that lack true leaves. In some of these simple plants, however, the green food-making tissues look like tiny leaves.