An analysis of the vegetative and reproductive anatomy of Sargassum lapazeanum was performed based on extensive sampling in three areas within its geographical range: a) San Juan de la Costa, b) Punta Calera, c) Punta Machos. Material was collected from low intertidal to subtidal populations and evaluated based on variations present within and between populations. Our goal was to comprehensively analyze the features of the vegetative and reproductive anatomy of this species. Our observations showed that this species has cauline, which is anatomically composed of three tissues layers. This species is dioic, with male and female conceptacles in the same receptacle but with different maturation times. The present study confirmed the presence of cauline in this species; this structure was previously described for some species in the Gulf of California, such as Sargassum horridum, and for several species in Japan. This structure could be responsible for the growth of primary branches and may also generate a new plant. This trend might explain the perennial nature of this species at the population level. Field and laboratory experiments could help to delimit the ecophysiological conditions under which this structure starts to develop.