Deana Mitchell, age 14, of bowling Green, Ohio, for her question:
ARE THERE MANY KINDS OF FLOWERING PLANTS?
The largest and most highly developed family of flowering plants is called the composite family. It consists of more than 20,000 species of flowering herbs and shrubs. Legume is the name given to any of the plants that belong to the pea family. They make up the second largest family of flowering plants. There are about 13,000 species of legumes.
Composite plants have efficient methods of reproduction. They can produce many seeds and have good methods of scattering them.
Each flower head is a composite of many small flowers. The heads are usually made up of two kinds of flowers: the ray and the disk flowers. In the sunflower, for example, ray flowers form the yellow outer fringe of the flower head. Disk or tubular flowers make up the inner brown disk.
Only a few composite plants, including endive, chicory, lettuce and artichoke, are used as food for man. Some, such as camomile, tansy and arnica, are used to make drugs. Asters, chrysanthemums and dahlias are grown for their beauty. Weeds and wildflowers of the composite family include ragweed, goldenrod, sagebrush and thistles.
Many legumes are of great economic importance throughout the world. Such legumes as peas, beans and peanuts are valuable foods. Alfalfa, clover and vetch are important forage and pasture plants. Other kinds of leguminous plants yield medicines, dyes, oils and timber.
Legumes grow in most parts of the world. They vary widely and may be trees, shrubs or herbs. Many are climbing plants.
The group gets its name from the legumes (seed pods) that most of the plants bear.
The flowers of one large subfamily of legumes look like butterflies. Botanists call this group Papilionideae, from the Latin word for "butterfly." The common sweet pea belongs to this group.
Legumes take nitrogen into their roots from the air. Certain bacteria, called rhizobia, live in nodules (knotlike growths) that form along the roots of the plants.) These bacteria take nitrogen from the air and change it into forms that can be used by plants.
This characteristic makes leguminous plants valuable in agriculture. Farmers often use them as green manure and as cover crops to improve poor soil.
Legume flowers are quite variable, but in all of them the bases of the five sepals (outer floral whorls) and five petals (inner floral whorls) and the stamens (male floral parts) are fused to form a cup (hypanthium) about the base of the ovary (female floral structure).
Usually 10 stamens are found. They either are fused into a single structure or occur as two groups, one containing nine stamens and one containing a single stamen.
The ovary, which matures into the fruit, consists of a single carpel (egg bearing structure) and is superior that is, borne above the other floral parts.