Isolates of Oscillatoria cluster 5, with distinctly pointed or "hooked" terminal cells, conform to some species included by Anagnostidis and Komarek (1988} in the genus Gcitknnema. However, the reference strain of this cluster (PCC 6504) shows a high degree of genetic relatedness neither to members of Geitknnema, nor to any representatives of the other four subclusters of Oscillatoria.