Aecidium is a genus of rust fungi in the Pucciniales order. The widespread genus is estimated to contain about 600 species. == Selected species == ...
An aecium with a cup-like outer wall. (pl. aecidia). 
• (n.) A form of fruit in the cycle of development of the Rusts or Brands, an order of fungi, formerly considered independent plants.
A cup-shaped aecium that contains a peridium.
an aecium in which the spores are always formed in chains and enclosed in a cup-shaped peridium.