XVI International Botanical Congess

Studies of the genus *Padina* along the Gulf of California were undetaken to determine how many species are present and which characters might be used to delimit species. After analysis of hundred of recent collections and material from several Herbaria our preliminar observations suggest that only 2 phenological groups could be segregated from five previously known. The presence of calcification, the combination in the number of cells in the base and the tip of the thalli and the morphology of reproductive structures were important to delimit phenological groups.