In this work, a new genus and species, Natantisphyllum crenae from the Late Cretaceous, central-western Argentina, assigned to the family Araceae was described based on fossil vegetative remains. The morphology of the leaves, especially the venation pattern of several vein orders, were compared with leaves of fossil and extant floating aquatic aroids. We performed a phylogenetic analysis to test the position of the new fossil in a phylogenetic tree and its relationship with other living and fossil representatives of Araceae. Natantisphyllum crenae possesses an unique combination of characters, then it cannot be placed within any other fossil or extant recognised aroid taxa and constitutes the southernmost record of a floating aquatic aroid. The phylogenetic relationships of the new fossil with other members of Araceae suggest that N. crenae is closely related to the fossil Aquaephyllum auriculatum. Both fossils from South America appear related to the modern aquatic Pistia and Lemnoideae and the fossil taxa from North America (Lymnobiophyllum and Cobbania) sharing a common ancestor.