The Collaborative International Dictionary of English v.0.48:

Podetium \Po*de"ti*um\, n.; pl. Podetia, E. Podetiums. [NL.,
   fr. Gr. ?, ?, foot.] (Bot.)
   A stalk which bears the fructification in some lichens, as in
   the so-called reindeer moss.
   [1913 Webster]

WordNet (r) 3.0 (2006):

podetium
    n 1: an organ or body resembling a stalk; especially the
         outgrowth of the thallus of certain lichens on which the
         ascocarp is borne