macrosporangium

from WordNet (r) 3.0 (2006)

macrosporangium
    n 1: a plant structure that produces megaspores [syn:
         {megasporangium}, {macrosporangium}]

from The Collaborative International Dictionary of English v.0.48

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.
   [1913 Webster]