The Collaborative International Dictionary of English v.0.48:

Stipe \Stipe\, n. [L. stipes a stock, post, branch: cf. F.
   stipe.] (Bot.)
   (a) The stalk or petiole of a frond, as of a fern.
   (b) The stalk of a pistil.
   (c) The trunk of a tree.
   (d) The stem of a fungus or mushroom.
       [1913 Webster]

WordNet (r) 3.0 (2006):

stipe
    n 1: supporting stalk or stem-like structure especially of a
         pistil or fern frond or supporting a mushroom cap