A new Carboniferous Equisetal from western Gondwana

CÉSARI, S.N.; PEREZ LOINAZE, V.S.

Gramado, RS, Brasil

Otro; XI Reunião de Paleobotânicos e Palinólogos; 2004

Universidad Federal do Rio Grande do Sul

Fertile and vegetative equisetalean specimens from the El Retamo Formation (Calingasta-Uspallata Basin), Upper Carboniferous, of western Argentina are described for the first time. This stratigraphic unit also contains frond remains of Nothorhacopteris argentinica and Botrychiopsis weissiana, species that characterize the NBG biozone. The studied specimens show at least three-orders of branches that produce whorls of leaves or slender and narrow branches. Leaves are narrow, once or twice dichotomized, arranged in whorls of up to 15 foliar units apparentely free from the base. Three fertile specimens bear whorls of sporangia immediately below bract whorls, encompassing half of the internode. Despite being poorly preserved it is possible to observe at least three whorls of sporangia and their elongate shape. According to the classification of Boureau, only the families Archaeocalamitaceae and Autophyllitaceae have furcate foliar units. Archaeocalamites differs in the more furcate leaves and in the associated reproductive structures.  On the other hand, the family Autophyllaceae is characterized by sporangiophores contained in cones born in the axil of the foliar whorl. Among Gondwanic species, Barakaria dichotoma differs in the sporangiophores arranged in terminal cones. Giridia indica is similar in the fructification but the leaves are basally fused and they are assigned to Phylloteca indica. New Permian taxa from Patagonia, with whorls of sporangiophores in the internodes, were recently reported. They probably integrate, together with this Carboniferous species, a western gondwanic natural group.