Fossil Araceae from the Upper Cretaceous of Patagonia, Argentina, with implications on the origin of free-floating aquatic aroids

• We describe a new fossil genus and species with affinities to aquatic Araceae.
• The new fossil taxon was found in association with Pandaniidites type pollen grains.
• Phylogenetic analysis places the new taxon in a close relationship with Lemnoideae.
• The fossil represents the first record of lemnaceous leaves for the S. Hemisphere.

Herein, we describe and name a new fossil genus and species, Aquaephyllum auriculatum, and report on the presence of Pandaniidites pollen grains from La Colonia Formation (Maastrichtian, Upper Cretaceous), Patagonia, Argentina. The new fossil taxon is based on leaf impressions and is morphologically similar to members of the family Araceae, subfamily Lemnoideae. The most important morphological characters comprise the adaxial venation with at least eight primary veins, the crenate margin, and the presence of an auricle with a floating function. Phylogenetic analysis places the new taxon in a close relationship within the subfamily Lemnoideae, which also includes the fossils Limnobiophyllum scutatum, Cobbania corrugata, and the extant Pistia stratiotes. Aquaephyllum auriculatum and Pandaniidites are the first fossil record of lemnaceous leaves and the oldest record for Pandaniidites pollen for the Southern Hemisphere respectively. The inclusion of Aquaephyllum and Pandaniidites within a phylogenetic context confirms the previously suggested hypothesis on the existence of close relationships between modern Pistia, and the fossils Limnobiophyllum and Cobbania.