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the multicellular organ of heterosporous Pteridophyta and seed plants in which the microspores develop. In Selaginella and Sigillaria the microsporangia are located singly in the axils of microsporophylls or on the upper-sides of the leaves (in Lepidodendron, Pleuromeia, and Isoetes). In Pleuromeia and Isoetes they are submerged in a special cavity. In some extinct ferns the microsporangia are on the underside of the sporophylls. In water ferns they are formed in sporocarps: 64 microspores develop in the microsporangium of Sahinia, and 32 or 64 in the microsporangium of Marsilea. In gymnosperms the microsporangia develop singly on microsporophylls (in some joint firs); more often several develop on a microsporophyll, arranged singly (conifers), in sori (many sago palms, ginkgoes) or in synangia (Caytoniales, many Bennettitales, Ephedra, Welwitschia). In angiosperms the pollen sac of the anther is homologous to the microsporangium.