A study of Lestes “virens” in Algeria, based on SEM, size analysis, and molecular analysis of nuclear ribosomal DNA genes (18S, 5.8S) and spacers (ITS1 and 2), reveals the presence of two taxa that can be separated by the length and sequence of their ITS 1 and their adult coloration, but not by molecular features in their 18S and 5.8S genes, the ITS2 spacer, and morphology. This contrasts with the Enallagma cyathigerum-group, where geographically defined morphological differences were unaccompanied by differences in ITS1 and ITS2. Previous ecological data had shown the first lestid to be a summer, and the second an autumnal reproducer. The red autumnal species is here named Lestes numidicus sp. n. (holotype <J, allotype 9; Algeria, Lac des Oiseaux, X-1993; deposited in IRSN, Brussels); the status of the green summer species is discussed. It probably corresponds to L. virens, but this is likely to be a hybrid taxon, resulting from the postglacial introgression of L. numidicus with a taxon invading from the East, via the Iberian Peninsula, L. virens vestalis from France is likely to be introgressed as well. In case this hypothesis is confirmed, the first junior synonym available, L. marikovskii (Belyshev) from Kazakhstan, applies to the taxon extending from Kazakhstan-Tajikistan to Central Europe.