Flowers arise from apical meristems similar to vegetative shoots but, unlike them, have determinate growth. The floral primordia develop into four different kinds of specialized leaves that are borne in whorls at the tip of the stem (see Figure
1 ). The two outer whorls are sterile, the inner two fertile. The first formed outer whorl—the
calyx— is the most leaflike and its individual parts, the
sepals, often are green. The
petals of the next whorl, the
corolla, frequently are brightly colored and in a majority of flowers retain some semblance to leaves. (Together the calyx and the corolla are called the
perianth.) The next two whorls, the
androecium and the
gynoecium, are composed of highly modified reproductive structures that have lost their leaf-like appearance. The androecium is composed of
stamens and the gynoecium of
carpels. (
Pistil is sometimes used as the term for a single carpel or a group of fused carpels.) The stamens are microsporophylls and have a stalk, the
filament, at the top of which the
pollen-bearing
anthers are located. A carpel is a megasporophyll and has as its base an enlarged
ovary from which the
style bearing a
stigma arises. The whorls are attached to the
receptacle area at the end of the flower stalk or
pedicel. Some flowers arise singly, but more are produced and arranged in groups called
inflorescences. The stalk of an inflorescence is the
peduncle and the extension of the axis in the inflorescence is the
rachis, to which the pedicels of the individual flowers are attached.
It is tempting, but botanically incorrect, to refer to the stamens as “male” floral parts and the carpels as “female” since both are part of the
sporophyte generation and only gamete-producing plants, i.e. gametophytes, have gender. The male gametophytes of angiosperms develop within the anthers, the female in the ovules.
Themes of Plant Biology
The Shoot System: Flowers, Fruits, Seeds
