Flowers reinvented plant sex in the Jurassic era
Flowers are the reproductive organs of angiosperms, typically arranged in four concentric whorls around a tip. They first evolved in the Jurassic, roughly 150 to 190 million years ago, and helped flowering plants dominate many ecosystems once occupied by cone-bearing rivals.
A complete flower stacks four whorls on a short axis called the receptacle, the thickened top of the flower stalk or pedicel. From the base upward come the calyx of sepals, the petals, the pollen-bearing androecium and the gynoecium that receives pollen. Sepals are tough, waxy and quick-growing, shielding the bud and often staying on to guard the fruit. Petals, almost free of fibre, are coloured, shaped or scented to recruit pollinators, and many carry ultraviolet markings that people cannot see but visiting animals can. A cluster of flowers is known as an inflorescence.
Every flowering plant is heterosporous. Meiosis inside the anthers yields microspores that become pollen, while ovules in the ovary produce megaspores that become embryo sacs; both gametophytes carry a single set of chromosomes. Pollen travels by bird, insect, wind or water, either between plants or within one bloom. Plants tend to favour cross-pollination because pairing genetically distinct partners raises diversity. After fertilisation the new cell grows into a seed holding an embryo, usually a food store and a protective coat, while the female part swells into fruit and the other floral organs wither.
Flowers arose in the Jurassic, some 150 to 190 million years back, and their reproductive efficiency let flowering plants displace non-flowering ones across many ecosystems. They now dominate most of the world's habitats, from tiny orchids to staple crops and large trees. Individual blooms span an astonishing range, from 0.1 millimetres to a full metre across. Botanists restrict the word to angiosperms and treat cones as the gymnosperm counterpart.
The English word came through Old French flor from Latin flōs. Until the 17th century the spelling flour was usual, before that form narrowed to mean ground grain, originally a figurative sense of the finest part. Blossom, the Old English term, now mostly refers to the flowers of fruit trees, and flower, bloom and blossom all descend from one Proto-Indo-European root meaning blossoming.
Source: Flower
