Morphological Variation of Cymbella delicatula and C. hustedtii from Northern Lake Michigan

Abstract

Morphological variation of 2 Cymbella spp. from a collection at South Fox Island, Lake Michigan [USA] is discussed. Populations are compared to treatments in the taxonomic literature, and variation indices are used to determine whether distinct growth forms or varieties are present. Although C. delicatula initially appeared to have 3 defined morphological series, these are interpreted as part of one continuously variable population. The C. hustedtii population appears to be a single variable group. Descriptions and photographs accounting for intraspecific variation are given for both species, and comparisons are made to other Cymbella spp. in the collection.