The Collaborative International Dictionary of English v.0.48:

Trifoliate \Tri*fo"li*ate\, Trifoliated \Tri*fo"li*a`ted\, a.
   [Tri- + foliate. Cf. Trefoil.] (Bot.)
   Having three leaves or leaflets, as clover. See Illust. of
   Shamrock.
   [1913 Webster]

WordNet (r) 3.0 (2006):

trifoliate
    adj 1: (of a leaf shape) having three leaflets [syn:
           trifoliate, trifoliolate, trifoliated]