Reproductive and vegetative organs with affinities to Haloragaceae from the Upper Cretaceous Huepac Chert Locality of Sonora, Mexico

From the Upper Cretaceous (Maastrichtian-Campanian) Huepac Chert Locality o f the Tarahumara Formation, a new extinct aquatic plant of the Haloragaceae (Subclass: Rosidae), Tarahumara sophiae Hernandez-Castillo and Cevallos-Fe rriz. is presented. It is reconstructed on the basis of both reproductive a nd vegetative organs preserved in chert. Its description and comparison wit h extant plants are based on the analysis of 350 permanent slides made with thin section and peel techniques. A mosaic of anatomical and morphological characters found in the extant Myriophyllum, Meziella, and Haloragodendron is used to characterize the new ta,von. The development from flower to fru it in the fossil plant follows similar stages found in some extant species of Myriophyllum. However, a floral cup is reported for the first time in th e family, and it is compared to the persistent fused sepals (terminal coron a) of Meziella. This plant reconstruction increases the morphological diver sity of the Haloragaceae, demonstrates the presence of a new dispersal mech anism compared with those known for the family, suggests that this lineage had originated by at least the Upper Cretaceous, and refutes the interpreta tion of several haloragacean Tertiary reports as representing genera of ext ant plants.