Structure and reproduction of the genus Ceramium (Ceramiales, Rhodophyta) from Oregon, USA

Six species of Ceramium (Rhodophyta) are recognized in the intertidal zone of Oregon, USA. Of these, C. californicum, C. codicola, C. gardneri, and C. pacificum are endemic to the north-eastern Pacific, while Ceramium cimbricum and Ceramium kondoi, previously known only from the north-western Pacific and Alaska, are newly reported from Oregon. Detailed descriptions and illustrations of vegetative and reproductive development in C. californicum, C. codicola, C. gardneri, and C pacificum are presented for the first time, and lectotypes of C. californicum, C. gardneri, and C. pacificum are designated. Although female and male reproductive structures of all these species were found to be similar and are characteristic of the genus, the development of the cortical nodes and tetrasporangia shows that these species fall into three groups: (1) C. codicola, C. kondoi, and C. pacificum, which are completely corticated and produce tetrasporangia in an alternate sequence; (2) C. californicum, which is incompletely corticated with filamentous rhizoidal cells and produces tetrasporangia in an opposite sequence; and (3) C. cimbricum and C. gardneri, which are incompletely corticated and produce tetrasporangia initially from the last-formed periaxial cell. Our morphological and anatomical observations suggest that the genus Ceramium may need to be divided into different infrageneric groups or into different genera.