The Collaborative International Dictionary
Macrosporangium \Mac`ro*spo*ran"gi*um\, n. [NL. See Macro-, and Sporangium.] (Bot.) A sporangium or conceptacle containing only large spores; -- opposed to microsporangium. Both are found in the genera Selaginella, Isoctes, and Marsilia, plants remotely allied to ferns.
n. (context botany English) A megasporangium; sporangium or conceptacle containing only large spores; opposed to microsporangium.