The aim of this study was to analyze the diverse fungal palynomorphs present in the Cullen Formation (Miocene), included in the Austral Basin, along the NE coastal region of the Isla Grande in Tierra del Fuego, Argentina. Fifty four form genera including eighty species of fossil fungal spores were recognized. In addition nine genera and eight species of fungal fruting bodies, most belonging to the extant Microthyriaceae (Ascomycota), are present. Other remains (hyphae, conidiophores) were also present. Many spores, fruiting bodies, and other fungal structures, could not be assigned to any known extant or fossil genera. Of the total fungal palynomorphs, 34 genera including 74 species of spores, as well as 5 genera and 4 species of fruiting bodies, are described for the first time in Argentina, enlarging the geographical distribution, and in some cases the stratigraphic occurrence. Several taxa suggest a tropical to subtropical paleoenvironment with high humidity indexes. The presence of certain fungal spores (Ornasporonites inaequalis, Brachysporisporites tenuis) and fruiting bodies (Microthyriella diporata, Phragmothyrites kiandrensis), provide a biostratigraphic index suggesting a Miocene age for the Cullen Formation. Both paleoenviromental and biostratigraphic conclusions are coincident with those based on other palynological and sedimentary evidence.

Key words: Argentina, Fungal spores, Microthyriaceae, Miocene