Microspore, the small or male spore in the heterosporous Pteridophyta (q.v.), such as Selagi-. nella and the Rhizocarps (q.v.), in which there are two kinds of spores. The microspores are small and generally unicellular, resembling pollen-grains in structure, though not in function. They germinate, each producing a small and simple male prothallium and antheridium.