What is "microspore"

Microspore \Mi"cro*spore\ (m[imac]"kr[-o]*sp[=o]r), n. [Micro- + spore.] (Bot.) One of the exceedingly minute spores found in certain flowerless plants, as Selaginella and Isoetes, which bear two kinds of spores, one very much smaller than the other. Cf. Macrospore.

1856, from micro- + spore.

n. (context botany English) Smaller of the two spore produced by plants, compare megaspore.

n. smaller of the two types of spore produced in heterosporous plants; develops in the pollen sac into a male gametophyte

Microspores are land plant spores that develop into male gametophytes, whereas megaspores develop into female gametophytes. The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Microspores are structures that are part of the alternation of generations in many seedless vascular cryptogams, all gymnosperms and all angiosperms. Plants with heterosporous life cycles using microspores and megaspores arose independently in several plant groups during the Devonian period. Microspores are haploid, and are produced from diploid microsporocytes by meiosis.