The Angiosperm Life Cycle

Angiosperms—the most diverse group of plants on Earth—include flowering and fruiting trees, grasses, vegetables, and other flowering plants. 

The life cycle of angiosperms is dominated by the spore-generating sporophyte stage, rather than the sexual gametophyte stage. 

Like conifers, angiosperms produce two types of spores. 

These male and female gametes are produced in distinct reproductive flower organs. 

Megaspores are produced in carpels. A carpel includes an ovary and its ovules. Each ovule contains a megasporangium, where megaspores are produced.

Within each megasporangium is a megasporocyte—a megaspore mother cell. A megasporocyte produces four megaspores through meiosis; one survives and develops into an embryo sac, which consists of an egg and a small number of other cells. 

Microspores originate in the flower anthers at the tips of stamens. Within the anthers are microsporangia containing microsporocytes. Microsporocytes produce microspores through meiosis. 

A microspore develops into a pollen grain, which contains a tube cell and a generative cell. After the pollen reaches a stigma - the upper part of the carpel - the tube cell becomes a pollen tube. The pollen tube exte