Dictyota crenulata J. Agardh is widely distributed throughout the Gulf of California. Comparative analyses of morphology, anatomy, and reproductive features of this species were conducted along the central western and southwestern regions of the Gulf of California. Thalli showed geographical variations in length and apical width. No differences were observed in anatomy of vegetative thalli or relative abundance of reproductive structures. Dictyota crenulata had unilayered or multilayered medullas in the basal region and in proliferations. Most thalli presented unilayered medullas in the middle section. Our observations indicate that number of medullary layers is indeed a phenotypically plastic character, in agreement with previously published results. Variations in thallus morphology such as proliferations and length are likely the result of environmental differences, also reflected in the reproduction of D. crenulata. The southwestern region had the highest percentage of all life cycle stages (female gametophytes and sporophytes, both 22%, and vegetative thalli, 14%). Our results demonstrate morphological variability in Dictyota crenulata across its distribution in the Gulf of California.