Describe the purpose of a flower, identify the four floral whorls and describe their function in individual flowers.
The angiosperms (Phylum Anthophyta) are unique from the rest of the plant phyla in that they produce flowers and fruits as part of their sexual reproduction. Since plants are not mobile, they are not able to travel in order to seek mates, copulate, and disseminate their offspring. As a result, plants have evolved a number of novel strategies in order to accomplish these tasks. Flowers are modified in a variety of ways in order to facilitate pollination and seed dispersal, both by biotic and abiotic means.
The flower is the main distinguishing characteristic of the flowering plants (angiosperms). Although flowers come in various shapes, sizes and colours, they are all based on the same plan. The variation we observe reflects the many ways by which reproduction is accomplished.
A flower is a specialized reproductive shoot consisting of an axis bearing a maximum of four sets of ‘appendages’: sepals, petals, stamens, and carpels. These appendages are actually modified leaves (the flower is a modified branch). If all four sets of appendages are present, the two outer sets are sterile.
A “flower” is really nothing more than a shoot (stem and leaves) modified for reproduction. Flowers can arise singly or in clusters called inflorescences. A stem-like structure called a peduncle supports an inflorescence or a solitary flower. Pedicels are the structures which support individual flowers of an inflorescence. The end of the peduncle is often expanded to form a receptacle to which the actual floral parts attach. Flowers can have up to 4 whorls of flower parts. Working from the outside to the inside, the parts that make up those whorls include:
The outermost ones are the sepals. These are often greenish, and leaflike. In the bud they cover and protect the other flower parts. The sepals protect the flower during the bud stage. Some sepals are modified to look nearly identical to the petals, but they are always located to the outside of the actual petals. The collective whorl of sepals is referred to as a calyx.
The petals are found to the inside of the calyx and are often pigmented and showy in order to visually attract pollinators. Petals may be separate or fused; together, they are collectively referred to as a corolla.
The stamens consist of a stalk-like filament supporting a pollen-producing anther. The collective arrangement of stamens represents the male part of the plant and is referred to as the androecium (“house of men”).