Morphological and molecular evidence is provided to further document the status of the enigmatic taxon known as Caulerpa floridana W.R. Taylor from White Shoal, Dry Tortugas, Florida. DNA sequencing of three historical herbarium specimens (WRT329, WRT345 and WRT349) housed at the University of Michigan Herbarium (MICH) demonstrated the molecular separation of this species based on the reconstruction of 931 nucleotides of the chloroplast gene tufA. Caulerpa floridana is sister to the western Atlantic endemic C. ashmeadii Harvey and an unknown Caulerpa taxon from the Florida Middle Grounds. Caulerpa floridana most reliably differs from C. ashmeadii by the presence of a sharp, unequivocal apiculus at the tip of each pinnule. A morphological review of southwestern Atlantic records of C. floridana from Brazil excludes these reports as representative of the species.