Petals

Lore & Background

The collection of all petals in a flower is referred to as the corolla. The role of the corolla in plant evolution has been studied extensively since Charles Darwin postulated a theory of the origin of elongated corollae and corolla tubes. A corolla of separate petals, without fusion of individual segments, is apopetalous. If the petals are free from one another in the corolla, the plant is polypetalous or choripetalous; while if the petals are at least partially fused, it is gamopetalous or sympetalous. In the case of fused tepals, the term is syntepalous. Fused petals may form a tube, which is then known as a 'corolla tube'.

Reader's Guide

Petals are usually surrounded by an outer whorl of modified leaves called sepals, that collectively form the calyx and lie just beneath the corolla. The calyx and the corolla together make up the perianth. When the petals and sepals are difficult to distinguish, they are collectively called tepals. Petals can differ dramatically in different species. The number of petals in a flower may hold clues to a plant's classification. For example, flowers on eudicots most frequently have four or five petals while flowers on monocots have three or six petals, although there are many exceptions. The petal whorl or corolla may be either radially or bilaterally symmetrical. If all petals are essentially identical in size and shape, the flower is regular or actinomorphic. Many flowers are symmetrical in only one plane and are termed irregular or zygomorphic. In many plants of the aster family such as the sunflower, the circumference of the flower head is composed of ray florets, each with a single large petal. Florets in the centre of the disc typically have no or very reduced petals. In some plants such as Narcissus, the lower part of the petals or tepals are fused to form a floral cup (hypanthium) above the ovary. A petal often consists of two parts: the upper broader part called the blade, and the lower narrower part called the claw. Petals of different species vary greatly in colour or colour pattern, both in visible light and in ultraviolet. Such patterns often function as guides to pollinators and are variously known as nectar guides, pollen guides, and floral guides.

Did You Know?

• Wind-pollinated species such as the grasses often have very small petals or none at all.
• When the undifferentiated tepals resemble petals, they are referred to as 'petaloid', as in petaloid monocots.
• 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.
• Flowers that depend on wind pollination will produce large amounts of pollen because most of the pollen scattered by the wind tends to not reach other flowers.