Laurencia laurahuertana Mateo-Cid, Mendoza-González, Sentíes & Díaz-Larrea sp. nov. is described from Quintana Roo, Mexican Caribbean, on the basis of comparative morphology and ribulose bisphosphate carboxylase gene sequence analysis. It is distinguished from other Laurencia species by the small size of the sporophytes and dioecious gametophytes, the branching thalli, and its epiphytic habits. The phylogenetic analysis showed that the Mexican Caribbean sample, from Punta Herrero (Quintana Roo), formed a distinctive and well supported clade segregated from other species of Laurencia from Brazil and Mexico. The Mexican entity is morphologically and genetically distinct from other Laurencia species, warranting description as a new species.