Desmid of the month
December 2004

Euastrum oblongum

Like Staurastrum, Euastrum is an artificial genus, involving groups of species which apparently are but little related. The decisive (artificial) characteristic of the genus is in the cell apex showing a median incurvation, combined with an elliptic-rhomboid outline of the cell in top view. The apical incurvation in question may be a sharp (V-shaped) incision, a deep invagination or only a shallow depression. Euastrum oblongum is characterized by a deep, closed invagination *. Eu. oblongum is a fairly large-sized species, hardly to be confused with other species. Besides the median apical invagination there are several lateral invaginations resulting into multi-lobed semicells. In the Netherlands, Eu. oblongum is a common species in benthos and tychoplankton of sligthly acidic, mesotrophic water bodies. Zygospores, which are globular with numerous mamillate projections, on the contrary are of rather rare occurrence.

* For an example of a Euastrum species marked by just a shallow median apical depression, see Euastrum verrucosum.