A reevaluation of Aulacoseira nygaardii ( Camburn ) Camburn & D . F . Charles ( Bacillariophyceae ) : based on scanning electron microscopy of type material

Aulacoseira nygaardii was originally described by Camburn (as Melosira nygaardii in Camburn & Kingston 1986) based on light microscopy. Because the fine structure of this taxon can be difficult to resolve with light microscopy, positive identifications can also be difficult. We present an emended description of this taxon based on an evaluation of type material with scanning electron microscopy (SEM). Although SEM micrographs reported as A. nygaardii were presented by Scherer (1988), our observations indicate that the specimens examined by him possess several characters that differ from those in the type material and may represent a different organism.