A charophyte assemblage composed of six species has been recovered from lower Oligocene deposits of the Dâncu Formation at the fossil site of Suceag (Transylvanian Basin, Romania). The assemblage is dominated by the two varieties of the species Lychnothamnus pinguis (L. pinguis forma pinguis and L. pinguis forma major). Accessory species include Lychnothamnus prealangeri, Nitellopsis (Tectochara) merianii, and few Sphaerochara sp. and Harrisichara sp. gyrogonites. L. pinguis is the index species of the homonymous Rupelian European biozone which was previously correlated in Western Europe with the Mammal Paleogene Reference Levels of MP21–MP23, and calibrated with the Geomagnetic Polarity Time Scale (GPTS), chrones C13N and C12R. From a paleobiogeographic viewpoint, this study confirms the presence of L. pinguis forma pinguis and L. praelangeri in Romania and in the whole Eastern Europe. Moreover, the charophyte assemblage from Suceag belongs to the Priabonian–Rupelian European charophyte bioprovince. While the vertebrate fossils reported in the same fossil locality indicate that the Dâncu Formation at Suceag sedimented in an estuarine environment, the charophyte assemblage suggests a more complex pattern, with presence of freshwater lakes too.