Abstract

Recent studies have suggested that the species of Gelidiella and Parviphycus could be separated from small-sized species of Gelidium and Pterocladiella on the basis of attachment structures, in addition to or rather than by the presence or absence of internal rhizoids. Species of Gelidiella and Parviphycus attach to the substratum by single-celled rhizoids produced by the outermost cortical cells, while species of Gelidium and Pterocladiella attach by bundles of colorless rhizoidal filaments produced by inner cortical and external medullary cells. The type specimens of 12 species of Gelidiella were studied testing the above idea. Nine of these species (G. bornetti, G. hancockii, G. lingulata, G. lubrica, G. machrisiana, G. mexicana, G. nigrescens, G. ramellosa and G. stichidiospora) lacked internal rhizoids and attached to the substratum by single-celled, externally produced rhizoids. Two species (G. sanctarum and G. taylorii) exhibited internal rhizoids and Pterocladiella-type attachments, while specimens of one species (G. refugiensis) lacked attachment structures but exhibited internal rhizoids and polysporangia. Overall, results suggest that the presence of internal rhizoids and attachment structures are related characters that appear to be useful taxonomic tools to segregate Gelidiella and Parviphycus from other genera in the Order. Consequently, Gelidiella taylorii and Gelidiella sanctarum are transferred to the genus Pterocladiella and Gelidiella refugiensis to Gelidium.