DIVERSITY OF EARLY PERMIAN SPHENOPSIDS FROM PATAGONIA, ARGENTINA

CÚNEO, RUBÉN; ESCAPA, IGNACIO

Praga, República Checa

Conferencia; 7Th European Palaeobotany Conference; 2006

Sphenopsids is a group of particular importance in early Permian floras from Patagonia in southern Argentina. Both Sphenophyllales and Equisetales are conspicuously represented and highly diversified in the Río Genoa Formation. Interestingly, most taxa recorded occur through- out vegetative and reproductive organs, which allows a better interpre- tation in terms of natural taxa and then true diversity. Sphenophyllales are of course identified from the presence of the genus Sphenophyllum, which includes at least five species that closely resemble any Euroamer- ican Westfalian or early Permian assemblage, a fact unique for Gond- wana. More recently, additional forms have been discovered, including classical ribbed axes with leaf whorls of Sphenophyllum type but bearing in the same axes intercalated reproductive parts that resemble sphe- nophyll strobili in having modified leaves or bracts with axillar sporan- giophores. This organization clearly differs from the classical terminal structures typically seen in Sphenophyllostachis/Bowmanites. The Equisetales, on the other hand, appear more diversified includ- ing the lately described genera Peltotheca and Cruciaetheca, plus pos- sible calamitacean representatives like Annularia and Asterophyllites, with several species. A new morphotype recalls Cruciaetheca in showing fertile internodes between unmodified leaf whorls, however sporangi- ophores are disposed on the lower half of the internodes and bear much larger sporangia. Clearly, these highly diversified sphenopsid representatives sug- gest a definitely anomalous situation in terms of Gondwana paleoflo- ras at the beginning of the Permian. In this regard, strong affinities of this group of articulate plants with coeval records from Euramerica and Angara suggest a particular phytogeographic role of the Patagonian region in the early Permian floristic context. This is also important in terms of the phylogenetic context for many of these sphenopsids, par- ticularly Equisetales, which suggest a possible alternative scenario from the historical one regarding the origin and relationships of the modern Equisetum.