TAXONOMIC AND CULTURE STUDIES OF AGLAOTHAMNION OBSTIPUM SP. NOV. (CERAMIACEAE, RHODOPHYTA) FROM SOUTHEASTERN AUSTRALIA

A new member of the Tribe Callithamnieae, Aglaothamnion obstipum, is d escribed from shallow subtidal habitats in the Melbourne region of sou theastern Australia. Plants are delicate, caespitose, reach lengths of 35 mm, and grow primarily on two species of the encrusting corallinac eous genus Mesophyllum. Field populations are almost exclusively tetra sporic, although up to three successive cycles of a Polysiphonia-type life history have been completed in culture. Notable morphological fea tures of the new species are the 1-3 arching, adventitious branchlets that subtend the mature carposporophytes; the relatively large variabi lity in the shapes of the gonimolobes, which range in outline from rou nded to obcordate; the presence of 4-5(-7) simultaneously developing p rocarps irregularly distributed along the first 20 or so axial cells o n a given indeterminate axis; and the frequently recurved bearing bran ches of spermatangial axes, the cells of which are generally deflected at the point of attachment of the spermatangial clusters (the feature for which the species is named). Aglaothamnion obstipum appears to be anatomically similar to the cool-temperate Atlantic species A. westbr ookiae Rueness et L'Hardy-Halos, which apparently differs in the restr iction of procarps to a few axial cells near the apices of indetermina te axes; by the straighter, thinner and fewer numbers of subtending fi laments of the carposporophyte, the filaments also differing in having unmodified basal cells; by the undeflected bearing cells of spermatan gial axes; and the smaller and more widely spaced spermatangial cluste rs. Aglaothamnion obstipum is known for certain only from the Melbourn e region of Victoria, with a single W.H. Harvey record from 1855 sugge sting that the species could be native to that area.