Two rare and ill-known subtidal species of stalked, net-forming green algae, Struvea gardineri A.Gepp & E.Gepp and Phyllodictyon orientale (A.Gepp & E.Gepp) Kraft & M.J.Wynne, are re-described on the basis of the examination of type material and recent collections from the Maldives, Seychelles, and Socotra Island in the tropical Indian Ocean. The taxonomic position of both species is re-appraised on the basis of morphological data (cell division, branching pattern, tenacular cells, crystalline cell inclusions, cell shape, and cell dimensions) and molecular phylogenetic evidence (partial large subunit nuclear ribosomal DNA sequences). On the basis of the occurrence of segregative cell division in young plants of S. gardineri, this species is returned to its original genus, Struvea. Cell division in P. orientale takes place exclusively by centripetal wall ingrowths, confirming its placement in the genus Phyllodictyon as currently defined. However, morphological observations and molecular phylogenetic studies indicate that the delineation of genera on the basis of modes of cell division is problematic, and that the genera Struvea and Phyllodictyon, as presently conceived, almost certainly do not represent natural groups. |
