1. (pycnium, spermogonium) A flasklike structure produced by certain fungi (e.g. Puccinia and Leptosphaeria) in which asexual pycnospores (spermatid) are formed.
2. A spore-producing body formed by the fungal component of certain lichens, e.g. Parmelia physodes. It is a flask-shaped structure sunken in the thallus and opens to the surface by a pore. Inside the pycnidium are a number of conidiophores, which produce pycnoconidia. The functions of the pycnoconidia are uncertain though it appears that in some species they may, by behaving as male gametes, initiate ascocarp formation.