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Abstract
The generic placement of Gyrosigma obscurum (W. Smith) Griffith & Henfrey has been questioned in recent years, its position moving between Gyrosigma and Pleurosigma. The recent paper of Reid (2002a) caused some concern and Sterrenburg proposed that obscurum should be placed in Pleurosigma. This paper reinvestigates the claims of both Reid and Sterrenburg to conclude that the generic placement of obscurum is clearly more closely related to species of Gyrosigma than to species of Pleurosigma. Reanalyses of Reid's data set substituting the character coding advocated by Sterrenburg for striae arrangement and using the concepts of Sterrenburg in the cladistic analysis still shows that obscurum is more closely related to species of Gyrosigma than to species of Pleurosigma.