The Collaborative International Dictionary of English v.0.48:

Trilobate \Tri*lo"bate\, a. [Pref. tri- + lobate.]
   Having three lobes.
   [1913 Webster]

WordNet (r) 3.0 (2006):

trilobate
    adj 1: (of a leaf shape) divided into three lobes [syn:
           trilobate, trilobated, trilobed, three-lobed]