An Euastrum species (Conjugatophyceae, Streptophyta) was found in an agricultural ditch fed by a rheocrenic, slightly-hot spring ‘Ain El-Balad’ in the El-Farafra Oasis, Western Desert of Egypt. Morphotaxonomic diagnosis and autecology of this desmid species are hereby documented in detail and compared to other morphologically similar species and infraspecific taxa, particularly those of the species complex E. spinulosum. As compared to most other species of that complex, the newly described Euastrum species is mainly characterized by its distinctive small-sized cells, rather shallow and widely open invaginations between the semicell lobes and less pronounced apical lobes. Moreover, the basal lobes are broadly rounded and larger than the lateral lobes. We have named this interesting species E. elfarafraense sp. nov. after the type locality, the El-Farafra Oasis.