Bacidia gullahgeechee is described as new to science and easily recognized by the combination of a leprose thallus, minute tan to dark reddish-brown biatorine apothecia, and production of perlatolic acid. The species forms extensive, conspicuous colonies on palmetto (Sabal palmetto) trunks in maritime forests of the Ashepoo-Combahee-Edisto (ACE) Basin of South Carolina, one of largest protected estuaries in the eastern United States, where it is presumed to be narrowly endemic.