Hymenocallis ruenesiana is described and illustrated as a new species from the Yucatan Peninsula, Mexico. When comparing the morphological characters of the leaf, inflorescence, fruit and pollen, as well as the environmental conditions of the habitat of H. ruenesiana, discontinuities were found with those of Hymenocallis littoralis. Hymenocallis ruenesiana is endemic to the Yucatan peninsula, inhabiting seasonal savannas with clayey and floodable soils, while H. littoralis naturally inhabits the coasts, on easily drained sandy soils and it is also widely cultivated as an ornamental plant.