Morphological observations of Aulacoseira using scanning electron microscopy

Authors:
  • PSPeter A. Siver
    Peter A. Siver
  • HKHedy Kling
    Hedy Kling
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Abstract
Despite the fact that the genus Aulacoseira Thwaites is a common component of phytoplankton communities in many North American water bodies, there are relatively few taxonomic based surveys utilizing the scanning electron microscope (SEM). In addition, based on the current literature, some species are difficult to identify or distinguish from other taxa. We present taxonomic and morphological observations on 19 taxa based primarily on collections made in Connecticut, U.S.A., and from central and northern Canada. Aulacoseira ambigua (Grunow) Simonsen, Aulacoseira subarctica (O. Müller) Haworth, and Aulacoseira tenella (Nygaard) Simonsen were the most common species encountered in Connecticut, while Aulacoseira islandica (O. Müller) Simonsen, Aulacoseira granulata (Ehrenberg) Simonsen, A. subarctica, and A. ambigua were the dominant species from many central Canada localities. In the Canadian Shield region, specimens of the Aulacoseira disions (Ehrenberg) Simonsen group, the Aulacoseira lirata (Ehrenberg) Ross in Hartley group, and Aulacoseira perglabra (Oestrup) Haworth were more common. We had the most difficulty identifying taxa in the A. distorts and A. perglabra complexes and distinguishing A. lirata from Aulacoseira alpigena (Grunow) Krammer. The primary objectives of the paper were to provide an additional source of high-resolution SEM micrographs for many of the more common species of Aulacoseira, comment on the morphological detail of each taxon, and to discuss the difficulties we encountered using the current literature to identify some of the species. A few ecological observations are also provided. Lastly, we propose two new combinations, Aulacoseira pseudoamericana (Camburn) comb.nov. and Aulacoseira distans var. nivaloides (Camburn) comb.nov. Key words: diatoms, Aulacoseira, North America, taxonomy, morphology.

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