TRANQUILOXYLON PETRIELLAI NOV. GEN. ET SP. (PTERIDOSPERMALES) FROM THE UPPER TRIASSIC LAGUNA COLORADA FORMATION, SANTA CRUZ PROVINCE, ARGENTINA

The stem of a new genus and species, Tranquiloxylon petriellai with pteridospenn affinities, from the Upper Triassic of Patagonia is described. It is characterized by a parenchymatous pith with cells with dark contents surrounded by a continuous ring of primary xylern; the eccentric pycnoxylic wood is composed of closely packed wedge-shaped sections of secondary xylem with well marked growth rings, separated by vertical radial parenchymatic rays. The xylern bears uniseriate araucarioid borde red pits. Complex leaf-trace fonning structures are also described. This stem is compared with the Triassic Rhexoxylon, the Pennian Antarcticoxylon both from the Gondwana realm, and with Hermanophyton from the American Jurassic.