Source : Webster's Revised Unabridged Dictionary (1913)

Perfoliate \Per*fo"li*ate\, a. [Pref. per- + L. folium leaf.]
   1. (Bot.) Having the basal part produced around the stem; --
      said of leaves which the stem apparently passes directory
      through.

   2. (Zo["o]l.) Surrounded by a circle of hairs, or projections
      of any kind.

Source : WordNet®

perfoliate
     adj : of a leaf having the base united around (and apparently
           pierced by) the stem