Reproductive structures of Dictyopteris undulata (Dictyotales, Phaeophyceae) from Japan

sporophytes, and both male and female gametophytes of Dictyopteris undulata Holmes were collected from the Pacific coast and the Japan Sea coast of Japan. Female gametophytes are reported for the first time in the present study. All reproductive structures are aggregated in sori that form on both sides of the midrib in the upper and the middle parts of a blade. Tetraspor-angia are spherical and project from the cortical layer with a 2–4-celled stalk at the base. They are sometimes divided tetrahedrally to form four spores, but often remain undivided. Oogoniat sori also project from the cortical layer. Each oogonium is ovoid, sometimes borne on a single stalk cell at the base. Antheridial sori appear swollen above the cortex and each antheridium has a basal stalk cell. Fertile female gametophytes and te-trasporophytes are difficult to distinguish from each other in surface view because tetrasporangial and oogonial sori are similar in size and undivided tetrasporangia resemble oogonia. Oogonia are not so closely packed in small groups, unlike in Dictyota species, and they can be distinguished by the cell sizes (i.e. tetrasporangia are bigger in diameter than oogonia).