Genus and species concepts inZonariaandHomoeostrichus(Dictyotales, Phaeophyceae), including the description ofExallosorusgen. nov

Examination of type material, comparative studies on vegetative characters and data from published accounts of sporangia, gametangia and spermatozoids are used here to further develop and strengthen generic and species concepts in Zonaria and Homoeostrichus. Zonaria is characterized by octosporangia which lack a stalk cell and occur among whitish paraphyses, by the presence of cortical cells in indusiate sporangial and oogonial sori, and by slightly elongate sterile cells bordering the antheridial sori. Other characters (mucilage in sporangial and oogonial sori, biflagellate sperm with a row of many tall spines along the anterior flagellum) may also be diagnostic of Zonaria but have not been demonstrated in the generitype. Eight species are retained in Zonaria. Generic placement of Zonaria stipitata, described on vegetative characters, requires confirmation. Homoeostrichus, as typified by Homoeostrichus sinclairii, is defined by the presence of brown paraphyses in nonindusiate sporangial and oogonial sori...