What are annuals? Biennials? Perennials? Garden flowers are simply cultivated wildflowers. Some kinds of garden flowers are exactly like the wild species. Other kinds have been bred scientifically so that their blooms are more attractive than those of the wild variety. Garden flowers are grown on farms and in nurseries and greenhouses as well as in home gardens. Some kinds of garden flowers also make excellent house plants. Garden flowers can be divided into three main groups based on how long they live: (1) annuals, (2) biennials, and (3) perennials. Annuals are plants that sprout from seed, grow to full size, bloom, produce seeds, and die–all within one year or less. Biennials are plants that live two years. They do not produce flowers and seeds until their second year of growth, after which they die. Perennials live at least three years. They may or may not bloom during their first year of growth. But after perennials have begun to bloom, they may do so every year almost indefinitely, depending on their species.
Parts of a flower
A typical flower has four main parts. They are (1) the calyx, (2) the corolla, (3) the stamens, and (4) the pistils. The calyx forms the outermost part and consists of leaflike sepals. The corolla consists of the petals. The stamens and pistils make up a flower's reproductive parts.
World Book illustration by James Teason
In most flowers, each main part consists of three, four, or five elements or of multiples of three, four, or five elements. In a trillium, for example, three sepals form the calyx, and three petals form the corolla. The flower has six stamens, and the pistil is composed of three equal parts. The elements may be separate from one another, like the petals of a poppy or a rose. Or the elements may be fused (joined together). In flowers with fused petals, for example, the corolla is shaped like a tube, bell, trumpet, pouch, or saucer. Flowers that have such corollas include morning-glories, daffodils, and petunias. In such species as primroses and verbenas, the petals are fused at the base and free at the tip. The corolla thus has a tubelike or bell-like base and a fringed edge.
In buttercups, morning-glories, and most other flowers, all the main parts are arranged around the center of the flower in a circular fashion. If the flower is divided in half in any direction, the halves will be alike. Such flowers are radially symmetrical. Orchids, snapdragons, sweet peas, and certain other flowers can be divided into identical halves only if the blossoms are cut through lengthwise. Such kinds of flowers are bilaterally symmetrical.
The pistils
are the female, seed-bearing parts of a flower. Some flowers, including all members of a pea family, have only one pistil. But most flowers have two or more. In many species, the pistils are fused into one compound pistil. A compound pistil is often referred to simply as a pistil. The individual pistils that make up a compound pistil are called carpels.
Among most flowers, each pistil or carpel has three parts–a stigma, a style, and an ovary. The stigma is a sticky area at the top. The style consists of a slender tube that leads from the stigma to the ovary. The ovary is a hollow structure at the base. It contains one or more structures called ovules.
The classifying of flowers
Flowering plants make up the class (group) of plants called Anthopsida. This class is split up into two subclasses: (1) dicotyledons, also called dicots, and (2) monocotyledons, also known as monocots. Plants are grouped based on the structure of their seeds. The seeds of dicots have two tiny leaves called cotyledons. The seeds of monocots have only one cotyledon. In addition, the petals and other flower parts of most monocots grow in threes or in multiples of three, and the veins in their leaves parallel one another. The flower parts of most dicots grow in fours or fives or in multiples of four or five, and the veins in their leaves are branched rather than parallel. Of the approximately 250,000 species of flowering plants, about 190,000 are dicots and about 60,000 are monocots.
