The Importance of Flowers in Plant Classification
among different plants vary much more than do the leaves, roots, and stems.
If plants of one species are planted under different conditions, the flowers will be much alike although there may be differences in the green parts. A buckwheat plant grown in tap water, for example, may grow only a few inches long, bear only two small leaves, and one flower but that flower will be practically the same as the flower produced on a large, normal plant.
If it were not for the flower, many plants would be impossible to classify according to botanical type. The details of how the flower is made and the parts arranged, therefore, are important in grouping plants into families, and in subdividing families into genera and species. In classification, color is not important because it varies greatly. Ten plants of the common pansy may be often different shades and colors. More important in classification are the number of sepals, petals, stamens, and pistils, and how they are united with one another. Some flowers have their parts arranged like the spokes of a wheel so that the flower, cut along any diameter, is divided into two equal halves. Such a flower is called regular. Buttercups, anemones, tulips, and lilies are examples.
Others, such as the sweet pea, violet, pansy, and snapdragon, have petals that vary in shape and size in the same flower, and can be cut in only one direction to form two equal halves. These are called irregular flowers. The arrangement of flowers, alone or in different types of clusters, is also important. Some flowers—the violet and the daffodil, for instance grows in solitary fashion with a single blossom at the end of a stem. Others, such as the rambler rose and the wild geranium, occur in loose clusters. Often, the individual flowers branch off in a series from a main stem, as in the lily of the valley. In some plants, such as wheat, the flowers are densely placed around a central stem in a compact cluster called a spike. In other plants, the flowers form a flat-topped, umbrella-shaped mass called an umbel. This is the sort of cluster found in the wild carrot.
The most compact cluster of all is found in the family composite, which contains the daisies, asters, goldenrod, zinnias, calendulas, dandelions, and similar plants. Here, what appears to be a single flower is a whole crowd of tiny flowers packed tightly together and standing upright on a flat disk. In the dandelion, all these flowers are yellow. In the common daisy, the inner ones are yellow and outer ones called the ray Bowers are white. When you "pull petals off a daisy," you are really pulling apart a miniature bunch of flowers. This tight packing is a good method of insuring pollination for these flowers. A bee or a fly can hardly walk across one single daisy in full bloom without pollinating numbers of the flowers of which it is made.