Laurencia translucida sp. nov. (Ceramiales, Rhodophyta) from Brazil

In the course of ongoing studies of the genus Laurencia Lamouroux in Brazil, an anatomically different species has been found. It is unusual in having two layers of cortical cells-the outer translucent and less-pigmented, the inner pigmented-and secondary pit connections between pigmented cortical cells but absent between outer translucent cells. The general aspect of male branches is also distinctive, in that numerous fertile branchlets are produced successively in subapical position around the previous branchlets, and each fertile branchlet exhibits a terminal cup-shaped spermatangial pit with a discernible axial cell row at its base when seen in longitudinal section. Within the spermatangial pit, the male structures are typical of the ‘trichoblast type’. Vegetative axial segments have a trichoblast and two pericentral cells and the tetrasporangia are cut off abaxially from the third and fourth additionally produced pericentral cells of the fertile axial segments. This occurs in the many species of subgenus Chondrophycus, but the tetrasporangial arrangement is of the parallel type, as in subgenus Laurencia. Procarp-bearing segments cut off five pericentral cells, the fifth of which becomes the supporting cell as in the majority of the species in both subgenera. This set of characteristics makes it impossible to identify L. translucida with any described species, or to include it in a known subgenus. The taxon is here proposed as new to science, and its infrageneric position is discussed.