Any of the heterosporous plants' spores that produce male gametophytes. The microspore mother cell splits through meiosis inside the microsporangium to create four microspores, each of which will eventually develop into a pollen grain. The growing microspores receive nutrients from an inner layer of cells called the tapetum, which also supplies important elements to the pollen wall. Within each anther of the stamens are four clusters of cells known as microsporangia (pollen sacs). To create microspores, the microsporangia go through meiosis.