A
petal (from
Ancient Greek petalon "leaf", "thin plate") is one member or part of the
corolla of a
flower. The corolla is the name for all of the petals of a flower; the inner perianth
whorl, term used when this is not the same in appearance (color, shape) as the outermost whorl (the
calyx) and is used to attract
pollinators based on its
bright color. It is the inner part of the
perianth that comprises the sterile parts of a flower and consists of inner and outer
tepals. These tepals are usually differentiated into petals and
sepals. The term "tepal" is usually applied when the petals and sepals are similar in shape and color. In a "typical" flower the petals are showy and colored and surround the reproductive parts. The number of petals in a flower (see
merosity) is indicative of the plant's classification
eudicots (the largest group of
dicots) having typically four or five petals and
monocots and
magnoliids having three, or some multiple of three, petals.
[1]The genetics behind the formation of petals, in accordance with the ABC model of flower development, are that sepals, petals, stamens, and carpels are modified versions of each other. It seems that the mechanisms to form petals evolved a small number of times (perhaps only once), rather than evolving independently from stamens in a large number of plants.[2]
There exists considerable variation in form of petals among the flowering plants. The petals can be united towards the base, forming a floral tube. In some flowers, the entire perianth forms a cup (called a calyx tube) surrounding the gynoecium, with the sepals, petals, and stamens attached to the rim of the cup.
The flowers of some species lack or have very much reduced petals. These are often referred to as apetalous. Examples of flowers with much reduced perianths are found among the grasses.
