Flower

Clockwise from top: Strelitzia reginae, a pink rose, Epipactis palustris, and inflorescence of Dracophyllum traversii

Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants (angiosperms). Typically, they are structured in four sets, called whorls, around the end of a stalk. These whorls include: calyx, modified leaves; corolla, the petals; androecium, the male reproductive unit consisting of stamens and pollen; and gynoecium, the female part, containing style and stigma, which receives the pollen, and ovary, which contains the ovules. When arranged in groups, with our without modified leaves (bracts), they are known collectively as an inflorescence. Flowers can be described systematically using both formulae and diagrams.

Flowers grow out of an apical meristem (stem tip) and are controlled by the presence MADS-box genes. Simple models are used to describe this development. Flowers are heterospourous, and so produce both microspores and megaspores, which generally create male and female gametophytes (organism that leads to creation of sex cells) respectively. Pollination mediates the transport of pollen to the ovules in the ovaries, to facilitate sexual reproduction. It can occur between different plants, as in cross-pollination, or between flowers on the same plant–or even the same flower, as in self-pollination. Vectors transport the pollen between stamen and stigma. They may be living animals, such as birds and insects, or non-living factors such as wind and water. Pollen, especially from wind-dispersing plants, is a large contributer to asthma

After pollination, fertilisation occurs. It involves both plasmogamy (fusion of cells excluding the cell wall) and karyogamy (fusion of the nuclei). The result is a diploid (two copies of each chromosome) cell called a zygote. Through cell and nuclear devision (mitosis) the zygote grows into a seed, which contains structures to assist in the future plants survival and success. At the same time, the ovary forms into a fruit, and the other floral structures die. Its function is to protect the seed and aid in dispersal. This dispersal is divided into external vectors (allochory or by the plant itself (autochory). External vectors include both living things, such as animals and insects, and non-living things, which includes wind and water.

Flowers evolved between 150 and 190 million years ago, during the later part of the Jurassic era and early Cretaceous. As a subgroup of seed plants, angiosperms used the flower to out compete them, as a result of greater efficiency. The colour of flowers assist in pollination and are the result of potosynthetic pigments. In taxonomy, which is the study of plant classification, flowers are a key tool used to differentiate plants. For thousands of years humans have used flowers for a variety of purposes including: decoration, medicine, food, and perfumes. In human cultures, flowers are used symbolically and feature in art, literature, religious practises, ritual, and festivals.