Linked from
The 8 pages that link to Microspore, each with the reason it gives.
StrobilusBroader topic: Microsporangia in some strobili release these male-gametophyte precursors.
HeterosporyBroader topic: It is the male-destined spore type produced alongside the megaspore.
IsoetesBroader topic: Quillwort microspores develop into male gametophytes that produce sperm.
SelaginellaBroader topic: Selaginella microspores develop into male gametophytes.