The Collaborative International Dictionary of English v.0.48:

Orbiculate \Or*bic"u*late\, Orbiculated \Or*bic"u*la`ted\, a.
   [L. orbiculatus. See Orbicular.]
   Made, or being, in the form of an orb; having a circular, or
   nearly circular, or a spheroidal, outline.
   [1913 Webster]

   Orbiculate leaf (Bot.), a leaf whose outline is nearly
      circular.
      [1913 Webster]

WordNet (r) 3.0 (2006):

orbiculate leaf
    n 1: circular or nearly circular leaf