DASYA ROSLYNIAE SP-NOV (DASYACEAE, RHODOPHYTA), WITH A DISCUSSION ON GENERIC DISTINCTIONS AMONG DASYA, EUPOGODON, RHODOPTILUM, AND POGONOPHORELLA

Dasya roslyniae sp. nov. (Dasyaceae, Rhodophyta) is described from sub tidal habitats at Split Solitary Island (30 degrees 14'S, 153 degrees 11'E), New South Wales, Australia. The new species Is distinct within the genus due to its strongly compressed and secondarily bilaterally b ranched axes, differing from the majority of Dasya species that are te rete and secondarily radially organized. Pseudolaterals are quickly ca ducous on ventral and dorsal (transverse) surfaces but are persistent on lateral surfaces for short distances from the apex, leaving the bul k of the plants flattened and denuded. Its gross morphological charact ers are thus similar so those displayed by the genera Pogonophorella, Eupogodon (formerly known as Dasyopsis), and Rhodoptilum. Characters u sed for separating these genera and Dasya are, in some cases, overlapp ing and in need of critical evaluation. To the primarily radially orga nized taxa, determined by examination of divisions of the apical cell, are placed species of Dasya, six species now included in Eupogodon, a nd the type and only species of Pogonophorella californica. Examinatio n of the activity of the apical cells of Eupogodon planum and Rhodopti lum plumosum, the type species of their genera, confirms the primary b ilaterality of these two genera, and the traditional defining feature of Eupogodon (lack of discernible pericentral cells in cross-section o f indeterminate axes) is shown to be untenable. A secondary character that would separate Eupogodon and Rhodoptilum is the polysiphonons bas es of otherwise monosiphonous laterals (pseudolaterals) in Eupogodon a nd the monosiphonous bases in Rhodoptilum.