Paleozoic origin of the cycads - Mamay, Sergius H. 1920-2008 (Washington : United States Government Printing Office, 1976)
"Megasporophylls and associated plants parts from the Upper Pennsylvanian and Lower Permian rocks of the southwestern United States are interpreted as a lineage of cycads, derived from the pteridosperms. Cycadean foliage is thought to be derived from Paleozoic taeniopterids"
Keywords: CICADAS; PALEOBOTANICA -- ESTADOS UNIDOS