Flower structure
A flower structure 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:
- Sepals - often leaflike and green, 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.
- Petals - 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.
- Stamens - 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").
- Carpels - carpels are the female floral parts and lie to the inside of the androecium. A carpel consists of 3 parts:
- ovary - the broadened base of the carpel which contains the ovules;
- style - an elongated structure extending from the top of the ovary and through which the pollen tubes will grow in order to deliver sperm to the egg;
- stigma - the often sticky terminal end of the style which receives and adheres pollen grains. The carpels are referred to collectively as the gynoecium ("house of women").
The corolla and calyx together are known as the perianth and represent the infertile parts of the flower while the androecium and gynoecium represent the fertile (sexual) parts. A flower is considered "complete" if all 4 whorls are present and "incomplete" if 1 or more whorls are absent. "Perfect" flowers have both male and female parts present; "imperfect" flowers are either male or female.
When looking at a whole flower, if the floral parts can be arranged so that any cross section of the flower has a mirror image, it is called radially symmetric. If the flower only has only one cross section which produces a mirror image, the flower is described as having bilateral symmetry.