Cryptogamie, Algologie, 2018, 39 (2): 215-226 © 2018 Adac. Tous droits réservés doi/10.7872/crya/v39.iss2.2018.215 A new Euastrum species (Conjugatophyceae, Streptophyta) from the Western Desert of Egypt Abdullah A. SABER a* , Frans A.C. KOUWETS b , Elizabeth Y. HAWORTH c & Marco CANTONATI d a Botany Department, Faculty of Science, Ain Shams University, Abbassia Square-11566, Cairo, Egypt b RWS Center for Water Management, Department of Hydrobiology, zuiderwagenplein 2, 8224 AD Lelystad, The Netherlands c Freshwater Biological Association, Far Sawrey Ambleside LA22 0LP, United Kingdom d Museo delle Scienze – MUSE, Limnology and Phycology Section, Corso del Lavoro e della Scienza 3, I-38123 Trento, Italy Abstract – 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 infraspecifc 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. Desmids / Egypt / Euastrum elfarafraense / new species INTRODUCTION The genus Euastrum Ehrenberg ex Ralfs is generally considered one of the most representative taxa in the family Desmidiaceae (Gontcharov, 2008; Guiry, 2013). To date, there are about 244 species and infraspecies which are accepted taxonomically (Guiry & Guiry, 2017). Euastrum is highly heterogeneous from the morphological point of view. Accordingly, the recent molecular concatenated study of Gontcharov & Melkonian (2008) showed using multi-locus data that this genus is polyphyletic in origin, forming three well-delimited phylogenetic lineages. * Corresponding author: abdullah_elattar@sci.asu.edu.eg