Casuarinaceae, today restricted to the Australasian region, has an extensive fossil record. In this article, we evaluatepreviousrecordsandrecentfindingsfromPatagonia,whereCasuarinaceaeareknownfromtheTufolitas Laguna del Hunco (early Eocene) in northwestern Chubut, Argentina. Based on characters found in numerous branchlets, infructescences, and male inflorescences with pollen of theHaloragacidites harrisiitype, the presence of three fossil species within the genusGymnostoma is confirmed:G. patagonicumcomb. nov., G. archangelskyi sp.nov.,andG.argentinumsp.nov.Thisistheoldestworldwidereportofmaleinflorescences andthefirstrecord ofvegetativebranchletsandmaleinflorescencesforSouthAmerica.Thesefossilsareofparticularinterestbecause Casuarinaceae is now extinct in South America, and they support the view that the family was diverse and had widespread distribution during the early Eocene climatic optimum. The diverse Gymnostoma described here further strengthens biogeographic links between Paleogene floras of Patagonia and Australasia.