Cladistic analysis of some freshwater araphid diatoms (Bacillariophyta) with particular reference toDiatoma andMeridion |
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Authors: | David M Williams |
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Institution: | (1) Botany Department, The Natural History Museum, Cromwell Road, SW7 5BD London, UK |
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Abstract: | Interrelationships of the ribbed araphid diatoms have been reinvestigated using a cladistic analysis of a revised morphological dataset. The presence of silicified transapical ribs has previously been used to distinguish between different groups and its ability to serve as a distinguishing feature is reevaluated. The importance of valve symmetry, not fully appreciated in a previous paper, is examined. The evolution of heteropolarity, and its importance in taxonomy appear more complex than is implied by a simple dichotomy dividing groups of species into heteropolar and isopolar forms, involving an inferred evolutionary transformation from one condition to the other. This analysis proposes a close relationship betweenDiatoma, Fragilariforma, Asterionella, Distrionella, Meridion, Tabellaria, andTetracyclus. It also confirms the sub-division ofDiatoma into two closely related taxa. The genusMeridion, however, should not include both heteropolar and isopolar species in a single genus. Although the species are closely related, the isopolar species are more closely related toTabellaria andTetracyclus than they are to the heteropolar species ofMeridion. |
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Keywords: | Diatoms Diatoma Meridion Systematics morphology phylogeny cladistics |
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