Mac·ro·spo·ran·gi·um n. 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.
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macrosporangium
n : a plant structure that produces megaspores [syn: megasporangium]
[also: macrosporangia (pl)]