Source : Webster's Revised Unabridged Dictionary (1913)

Volva \Vol"va\, n. [L. volva, vulva, covering.] (Bot.)
   A saclike envelope of certain fungi, which bursts open as the
   plant develops.

Source : WordNet®

volva
     n : cuplike structure around the base of the stalk of certain
         fungi
     [also: {volvae} (pl)]