Department of Computer Science Zhongshan University Guangzhou 510275 People's Republic of China

摘要

Four taxa were recognized which produce multi-spined and spineless coenobia. The spiny and spineless specimens had different cell wall ultrastructures. These taxa were: Desmodesmus abundans, D. multiformis, D. pleiomorphus and the new species D. multivariabilis. The Scenedesmus kanionensis was reduced to a variety of D. pleiomorphus. D. komarekii is a species which under the light microscope is similar to D. multivariabilis and which has a comparable light and electron microscopical variability, but is distinguishable by the lack of lateral spines and different cell wall ultrastructure of the short-spined coenobia. The strain UTEX 831 of D. multivariabilis was labelled Scenedesmus kissii in HEOEWALD (1989), but this identification was not accepted here. D. multivariabilis as also D. pleiomorphus and D. multiformis are hitherto known only from isolates. While all spiny specimens of the multispined taxa cannot be distinguished or only with difficulty under the light or electron microscope, they are all distinguishable by the cell wall ultrastructure of their spineless coenobia and they are distinguishable by their ITS-2rDNA base alingment. According to the ITS-2rDNA studies, D. multivariabilis, D. pleiomorphus and D. subspicatus each formed their own cluster, D. abundans was found in a cluster with D. maximus, D. hystrix and D. pirkollei and D. komarekii (and according to literature data also D. multiformis) in a cluster with D. armatus. ITS-2 could not solve the phylogeny of these taxa, but it did show their affiliation to clusters.