Comparative valve morphology of selected species of Eunotia Ehr. (Bacillariophyceae)

Abstract

The valve morphology of twenty four taxa of the genus Eunotia from Texas and Alaska was examined with the light and scanning electron microscopes with particular emphasis on the terminal nodules, raphe, hyaline areas, striae patterns and labiate process. The labiate process is a good diagnostic character because this structure is found in all the species examined (except E. triodon) and its location is consistent within a species. Taxonomic groupings based on the location of the labiate process, striate patterns, raphe placement and the presence of spines are proposed. Evolutionary trends of each morphological character are outlined. The evolution of Eunotia at the varietal rank seems to exemplify phyletic gradualism; however, evolution between species and closely related genera seems to exemplify punctuated equilibria. Species discussed include: E. arcus, E. bidentula, E. diodon, E. elegans, E. exigua, E. flexuosa, E. flexuosa var. eurycephala, E. formica, E. hexaglyphis, E. lunaris, E. lunaris var. subarcuata, E. monodon var. constricta, E. naegeli, E. parallela, E. pectinalis var. undulata, E. pectinalis var. ventricosa, E. praerupta var. bidens, E. quaternaria, E. serra var. diadema, E. sudetica, E. triodon, E. valida, E. vanheurckii and E. zygodon.