The Mediterranean Sea is a hotspot for introduced marine species, including seaweeds. Among red algae, Grateloupia, with no less than eight introduced species, occupies a prominent position. Here, we report a large foliose Grateloupia species collected in Eastern Harbour, Alexandria, Egypt, which had previously been reported as G. acuminata and G. doryphora. Comparison of rbcL gene sequences revealed that the specimens represent G. gibbesii, a species originally described from Charleston, South Carolina, USA and potentially distributed in the warm temperate and tropical western Atlantic Ocean. The species has been known only from a single location in Alexandria since the early 1990s, it has not been reported in extensive surveys prior to that date, and there are no reports from other Mediterranean sites. This indicates a recent introduction, with shipping the likely vector. We describe the vegetative and reproductive morphology of G. gibbesii as the basis for evaluating variation in female reproductive structures and generic concepts in Grateloupia.