Carya porcina

from The Collaborative International Dictionary of English v.0.48

Pignut \Pig"nut\ (p[i^]g"n[u^]t), n. (Bot.)
   (a) See {Groundnut}
   (d) .
   (b) The bitter-flavored nut of a species of hickory ({Carya
       glabra} syn. {Carya porcina}); also, the tree itself.
       [1913 Webster]