The known collections of the genus Cora in continental North America north of Mexico, all restricted to Florida, are shown to belong to a single species, representing a previously unrecognized taxon formally described herein as C. timucua. Based on data of the fungal ITS barcoding marker, obtained through Sanger and Illumina sequencing from two historical collections, the new species is phylogenetically most closely related to C. casanarensis from Colombia and C. itabaiana from Brazil, although it is morphologically most similar to the only distantly related C. hymenocarpa from Costa Rica. Based on data from the Consortium of North American Lichen Herbaria (CNALH) and from the Global Biodiversity Information Facility (GBIF), most of the collections of C. timucua originate from around the turn of the 19th century, while a few were made in the second half of the 20th century, all between 1968 and 1985. Almost all collections originate from Florida sand pine scrub, apparently the preferred habitat of this taxon. Neither modern collections nor extant localities are known. Based on these findings and the substantial degree of land use change in Florida in the past decades, we assessed the conservation status of C. timucua using the IUCN Red List criteria and found that it should be classified as critically endangered (CR), in line with the status of another Florida endemic, Cladonia perforata, which was the first federally red-listed lichen in the United States. The most likely location where C. timucua may still be extant is Ocala National Forest in the north-central portion of the Florida peninsula, although recent macrolichen surveys in that area did not encounter this species.