PALYNOLOGICAL STUDY OF THE PUNTA DEL BARCO FORMATION (APTIAN), SANTA CRUZ PROVINCE, ARGENTINA: GYMNOSPERM POLLEN GRAINS AND CHARACTERIZATION OF THE FLORA. This contribution completes the palynological investigation of the Punta del Barco Formation (Baqueró Group) with gymnosperm pollen analysis, including a new species-Microcachryidites cesariae-, and provides a comprehensive analysis of the flora. This taphocenosis is an interesting example of the biota disturbances by volcanic events prevailing in Patagonia during the Aptian. Through the integration of megafloristic, lithological and palynological data an open forest is interpreted, which gradually lost its tree layer after successive episodes of volcanic ash fall, with the consequent progressive decrease in taxonomic diversity. The palynological assemblage allows recognizing the fern family Gleicheniaceae as a dominant component of this Aptian flora, being highly resistant to strong environmental stress. Primitive angiosperms and lycophytes also developed successfully in this context, being linked to freshwater bodies. In contrast, gymnosperms were the most vulnerable group to environmental stress caused by volcanic eruptions. Among them, the Araucariaceae and Podocarpaceae families are the most resistant and the only conifers -with Cupressaceae- inhabiting Andean-Patagonian forests today. In contrast, Cheirolepidiaceae, Pteridospermales and Bennettitales were most affected, and although restored from Albian, they became extinct later.