sporangium (spo-ran'-gi-um). An organ within which spores are produced and borne until their release; e.g., a pollen sac of a gymnosperm, an anther of an angiosperm, or the saclike structure in Fungi that produces spores endogenously. Pl: sporangia. Cf: megasporangium; microsporangium. Obsolete syn: spore case.