Carpels are the female parts of a flower.
Classical angiosperm phylogeny is based mainly on flower anatomy, and in particular, the arrangement and form of the principle parts. The fruiting body is used as well, but its structure is often apparent in the flowers. More recently, genetic studies have been employed to determine the relationship of various botanical groups to each other. Many parts of the old classification system have proven more or less consistent with these studies, but there have also been a large number of changes, even to large and well studied groups. The changes to the classical system have been far more extensive than in the animal kingdom, where the classical, anatomy-based phylogeny has held up remarkably well. As a result, botanical nomenclature has been undergoing a bit of a revolution in the last two decades, and the process (as of 2009) is still ongoing. A community known as the Angiosperm Phylogeny Group or APG has provided some centrality to this process, but there are many areas where no consensus has been reached. Botany has always been prone to what might be termed "vanity species" with some genera (e.g. hieracium, the hawkweeds) having thousands of specific scientific names. The recent trend has been to recognize certain species as highly variable; but history dies hard, especially for those who discovered and described the "species".
A flower is the reproductive unit of an angiosperm plant. There is an enormous variety of flowers, but all have some characteristics in common. The definitive characteristic of the angiosperms is the enclosed ovary, which contains and protects the developing seeds. Floral reproduction is bisexual, and flowers have "male" and "female" parts. The "male" or pollen-bearing part is called the stamen, and is composed of the filament and the anther. The "female" or seed-bearing part is called the pistil, and is composed of the ovary, the stigma, and the style. A flower may have exclusively male parts, exclusively female parts, or commonly, both. When there are separate flower types, both may occur on the same plant; occasionally a plant may bear only male or female flowers.
Surrounding the reproductive parts is the perianth, a double envelope consisting of an outer portion, the calyx, which forms the sepals, and an inner portion, the corolla, which forms the familiar petals. There may also be leafy elements, termed bracts, surrounding a flower. Individual flowers are often organized into a larger group or cluster, termed an inflorescence. The stalk supporting a single flower is called a pedicel, that supporting an inflorescence, or an isolated flower, a peduncle.