PLEUROSIGMA OBSCURUMW. SMITH OR GYROSIGMA OBSCURUM(W. SMITH) GRIFFITH ET HENFREY? THE TALE OF TWO GENERA

The generic placement of Gyrosigma obscurum(W. Smith) Griffith & Henfrey has been questioned in recent years, its position moving between Gyrosigmaand Pleurosigma.The recent paper of Reid (2002a) caused some concern and Sterrenburg proposed that obscurumshould be placed in Pleurosigma.This paper reinvestigates the claims of both Reid and Sterrenburg to conclude that the generic placement of obscurumis clearly more closely related to species of Gyrosigmathan 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 obscurumis more closely related to species of Gyrosigmathan to species of Pleurosigma.