Problems in the identification of "Sargassum duplicatum" group

The morphological variations of characteristics of leaves and vesicles were studied in a Sargassum duplication Bory population from Owase, Mie Prefecture, Japan. Even in this small population, four morphologically different plants (type 1, 2, 3 and 4) were distinguished by their characteristics of leave and vesicles, as follows. Type 1 had slender oblanceolate leaves and entire vesicles, type 2 had broader elliptical leaves and apiculated, or crowned or phyllocyst vesicles, type 3 had slender lanceolate leaves and variable vesicles, and type 4 had broader elliptical leaves and entire or apiculated vesicles, respectively. However, these all plants from Owase showed scutellate holdfasts and slightly compressed primary branches. From the characteristics of holdfast, primary branch and dioecious sexuality, all these plants (type 1 to 4) from Owase should be identified as Sargassum duplicatum Bory having very wide variation ranges of leaves and vesicles, regardless of few cup-shaped characteristic leaves. Typical S. duplicatum has been usually distinguished its morphology of cup-shaped leaves, vesicles with horn-like appendages and dioecious sexuality in the receptacles. On the other hand, typical S. crassifolium showed the leaves with double seriated margin, phyllocyst-like vesicles, and monoecious sexuality in the receptacles. However, there were some confusing on the morphology of these leaves and vesicles, so these two species were now called the member of "S. duplicatum" group including several species (S. cristaefolium, S. turbinatifolium, S, turbinarioides et al.). From the wide variation in the leaves and vesicles of S. duplicatum in Japan as above, we need furthermore study of morphological variations and DNA analysis on these species in the East Asian and Southeast Asian populations