Flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (angiosperms). The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs. Flowers may facilitate outcrossing (fusion of sperm and eggs from different individuals in a population) or allow selfing (fusion of sperm and egg from the same flower). Some flowers produce diaspores without fertilization. Flowers contain sporangia and are the site where gametophytes develop. Flowers give rise to fruit and seeds. Many flowers have evolved to be attractive to animals, so as to cause them to be vectors for the transfer of pollen.
A stereotypical flower consists of four kinds of structures attached to the tip of a short stalk. Each of these kinds of parts is arranged in a whorl on the receptacle. A whorl is an arrangement of sepals, petals, leaves, or branches that radiate from a single point and surround or wrap around the stem. A whorl consists of at least three elements.
Most flowers have four whorls:
- the calyx, a whorl of sepals
- the corolla, a whorl of petals
- the androecium, a whorl of stamens, including filaments and anther
- the gynecium, a whorl of the female parts of a flower: the stigma, style and ovary