What is a flower?

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants. The biological function of a flower is to effect reproduction. Flowers may facilitate cross pollination or even self pollination. They develop fruits and seeds and helps in producing a new offspring. Many flowers have evolved to be attractive to animals, so as to cause them to be vectors for the transfer of pollen.

In addition to facilitating the reproduction of flowering plants, flowers have long been admired and used by humans to beautify their environment, and also as objects of romance, ritual, religion, medicine and as a source of food.

4 floral whorls

The four floral whorls taken from periphery to centre are as follows:

• Calyx: It is the outermost whorl and floral leaves of this whorl are called sepals. Their function is that of protection of inner whorls and also that of photosyn­thesis when green. 

• Corolla: It is the second whorl of floral leaves which are called petals. These protect the inner two whorls and also function for attraction of insects for pol­lination. All flowers are showy, for example flowers of oaks are quite small and nondescript. Typically, if a flower has to attract a pollinator, it will have distinct color. Flowers pollinated by wind are usually less showy. Calyx and corolla are called accessory whorls of the flower. In some plants al­though two whorls are present they are not differentiated from one another. In such a case both whorls are called perianth and each part of the perianth is called tepal. If accessory whorls are absent in a flower it is called achlamydous flower (naked flower), if out of the two accessory whorls only one whorl is present it is called monochlamyd-ous flower and if both whorls are present it is called dichlamydous flower. 

• Androecium: This is third whorl of floral leaves and is the male reproduc­tive organ of the flower. Each modified floral leaf is called microsporophyll or stamen. The stamen has a pollen-containing anther that sits on top of the filament. 

• Gynoecium (Pistil): This is the last (fourth) central whorl of floral leaves and is the female reproductive organ of the flower. Each modified floral leaf is called megasporophyll or carpel. Each gynoecium is made up of one or more mega-sporophylls (carpels). The female reproductive part consists of the central pistil. It is here where the ovary and ovules reside. The top of the pistil or stigma is the receiver of the pollen. Gynoecium refers to these parts collectively. 

A perfect flower consists of all of the five main parts (including receptacle). It contains both the male and the female reproductive parts. This differs from an imperfect flower, which will have either the male or the female system. Such plants are called monoecious if male and female parts are on the same plant as in the case of oaks. If there are distinct male and female plants, they are said to be dioecious.