Image ©Henk Schulp
Vegetative cell of Euastrum oblongum showing a deep, closed median apical invagination and several lateral invaginations which are opened to a greater or lesser degree.
Cell dimensions (L x B): ca 150 x 75 µm.
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.
Image © Wim van den Broeke
Zygospore with adhering semicells of Euastrum oblongum as encountered in the Dutch nature reserve 'De Klosse', June 2003.