The record of Upper Paleozoic fossil wood is very scarce in Argentina and up to date there are no Devonian fossil woods described. Several studies of Permian pycnoxylic woods have been carried out (Archangelsky, 1960; Herbst and Crisafulli, 1997; Crisafulli et al ., 2000). There are some reports of Carboniferous fossil woods without detailed studies (Mésigos, 1953; Pujana, 2003) and only two Carboniferous species were described, Medullopitys menendezii Petriella (1982) from Mendoza and Phyllocladopitys petriellae Brea and Césari (1995) from San Juan. The latter is here revised and its description complemented with the study of new specimens from the same fossiliferous bearing strata but from a different locality. The diagnosis of the species is emended, and a new combination is proposed.
The Jejenes Formation was defined by Amos (1954) for sedimentary sequences cropping out in the eastern margin of the Sierra Chica de Zonda, south of San Juan city (figure 1). The fossiliferous locality Quebrada de la Mina was described in detail by Cladera et al . (2000) and is the same locality which Bracaccini (1946) called Quebrada de la Cantera de Mármol. Bracaccini (1946) described, at the base of the sequence, conglomerates of glacial origin, and to the upper part of the sequence he noted the presence of abundant paleoflora (see Vega, 1995; Vega and Archangelsky, 2001). This upper section also bears the material here studied.
The paleoflora of this unit is referred to the NBG biozone that characterizes the Upper Carboniferous of Argentina (Archangelsky et al ., 1987). There are many species of leaves such as Nothorhacopteris argentinica (Geinitz) Archangelsky, Sphenopteris sarmientoi Vega and Iannuzzi, Fedekurtzia argentina (Kurtz) Archangelsky, Diplothmema bodenbenderi (Kurtz) Césari, Rhacopteris szajnochai Kurtz, Triphyllopteris cuyana Leguizamon and Vega, Eusphenopteris sanjuanina (Kurtz) Césari emend . Césari et al ., Ginkgophyllum diazii Archangelsky and Arrondo and Cordaites sp. Also, there are pteridosperm reproductive structures such as Rinconadia archangelskyi Vega, Austrocalyx jejenensis Vega and Archangelsky, Polycalyx laterale Vega and Archangelsky. The palynological record includes monosaccate pollen grains and spores (Gutiérrez and Césari, 1987; Césari and Bercowski, 1997) that are referred to the biozone Raistrickia densa-Convolutispora muriornata of north-western Argentina. The only wood already described is the one revised in this paper and a polixylic stem was reported by Césari et al . (2005).
According to Cladera et al. (2000) the depositional paleoenvironment of the upper section of the Jejenes Formation corresponds to a lacustrine type with sporadic occurrence of fluvial systems. Recently, Kneller et al . (2004) made a complete paleoenvironmental analysis of all the sequence in the nearby locality Quebrada Grande, and was interpreted as the fill of a glacial valley and its tributaries in a paleofjord environment with catastrophic sedimentation (Kneller et al ., 2004).
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