Eyde, Richard H. Department of Botany, Smithsonian Institution, Washington, DC.
- Floral Diversity
- Concentric units
- Traits of early flowers
- Diversification and coevolution
- Embryo sac
- Pollen tube
- Additional Reading
A higher plant's sexual apparatus in the aggregate, including the parts that produce sex cells and closely associated attractive and protective parts (Fig. 1). “Flower” has been used broadly enough by some botanists to include the reproductive equipment of cycads, conifers, and other plants with naked seeds. Here, however, it will be limited, as is usual, to the angiosperms, plants with enclosed seeds and the unique reproductive process called double fertilization. In its most familiar form a flower is made up of four kinds of units arranged concentrically. The green sepals (collectively termed the calyx) are outermost, showy petals (the corolla) next, then the pollen-bearing units (stamens, androecium), and finally the centrally placed seedbearing units (carpels, gynoecium). This is the “complete” flower of early botanists, but it is only one of an almost overwhelming array of floral forms. One or more kinds of units may be lacking or hard to recognize depending on the species, and evolutionary modification has been so great in some groups of angiosperms that a flower cluster (inflorescence) can look like a single flower.
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