Preliminary phylogeny of the family Surirellaceae (Bacillariophyta)

The diatom family Surirellaceae Kützing (1844) currently includes seven genera: Surirella Turpin, Campylodiscus Ehrenberg ex Kützing, Cymatopleura Smith, Plagiodiscus Grunow & Eulenstein, Hydrosilicon Brun, Stenopterobia de Brébisson ex Van Heurck and Petrodictyon Mann (Round et al. 1990). A cladistic analysis using morphological data for 25 taxa was used to construct a preliminary phylogeny and investigate the evolutionary relationships at both the family and genus levels. Results from this analysis indicate that the family Surirellaceae is not monophyletic. The monophyly of the genera Cymatopleura and Stenopterobia was supported, while the genera Surirella and Campylodiscus were found to be polyphyletic. Mapping of character evolution has identified several instances of homoplasy including the circumferential raphe (the diagnostic feature of the family Surirellaceae ) and the position of the two valves of a frustule being perpendicular to one another (a diagnostic feature for the genus Campylodiscus ). In order to produce a more natural system of classification, a revision of the family Surirellaceae, especially within the genera Surirella and Campylodiscus, is reaquired.