Description: The genus Neidium within the order Naviculales, contains a large array of species that are never really abundant, live in a wide range of autecological conditions from alkaline to acidic, and are exclusively freshwater. The genus is easily distinguished by valve morphology, chloroplast structure and specifically the autapomorphic presence of renilimbia on the internal valve. Taxonomically, the confusion in identifying species dates back to C.G. Ehrenberg and P.T. Cleve with poor line drawing and weak descriptions documenting some of the common American and European species. Further, species show a wide range in grading morphological forms, which has created additional confusion in the literature. With access to the original Ehrenberg material and genetic analyses we have been able to sort out many of the old problematic taxa and have a more developed understanding of the phylogeny. At present there are greater than 300 described species, varieties and forms, most requiring re-examination and validation. Using morphology and genetics this presentation will explore 20-30 of the more prominent Neidium taxa with an emphasis on morphological relationships including structural complexity of longitudinal canals and the valve wall. Some of the taxa discussed will include N. affine, N. amphigomphus, N. ampliatum, Neidium beatyi, N. boyeri, N. dilatatum, N. distinctepunctatum, N. firma, N. fossum, N. hitchcockii, N. iridis, N. potapovae, and N. rudimentarum. The primary objectives of this talk will be to explore the wide morphological variability of valve forms within the genus Neidium. The presentation will also introduce the utility of adding genetic analyses to taxonomic studies, including a short presentation on an efficient way to make micropipettes for single diatom cell isolations.

Target Audience: The talk is aimed at anyone interested in diatom phylogeny and classification.