Ceratozamia euryphyllidia from Veracruz is described and illustrated. This species differs from all others in the genus in its very large, broad leaflets (9–16 cm wide) which have undulate margins, prominent veins, and a membranous to translucent texture at maturity. It is apparently related to a group of species which all have relatively small strobili and leaflets that are attenuate basally, oblanceolate to obovate, inequilateral, abruptly acuminate apically, and generally papyraceous to membranaceous. The allopatric species of this group inhabit moist to very wet areas. The wetter the habitat, the larger and thinner the leaflets. Thus, for example,C. latifolia which has the smallest leaflets grows in the driest habitat whereasC. euryphyllidia which grows in the wettest habitat has the largest leaflets in the genus.