POTAMOGETONACEAE FOSSIL FRUITS FROM THE TERTIARY OF PATAGONIA, ARGENTINA

The subcosmopolitan and aquatic monocot family Potamogetonaceae Berch. and J. Presl 1823 comprises extant and fossil genera. Its known fossil record is composed mainly of fruit remains, and it comes only from Eocene to Pliocene sediments of the Northern Hemisphere ( Europe, Saudi Arabia, and China). Recently, several fruits sharing characters with living and fossil Potamogetonaceae genera have been found within the Paleogene Baibian Beds, Chubut, Patagonia, Argentina. Fossils were collected at the Puesto Baibian locality, which outcrops at the eastern sector of the Sierra de La Colonia. Fossils are impressions/compressions of infructescences and isolated fruits and seeds preserved as molds and casts. The infructescences are probably racemes bearing fruits placed most likely in whorls of four each. Isolated fruits are small one-seeded bisymmetrical endocarps. Palynological studies of the beds show the presence of an assemblage similar to those found in sediments of the Northern Hemisphere where Potamogetonaceae fossil fruits were previously recorded. This report constitutes the first fossil record of Potamogetonaceae for the Southern Hemisphere.