Isothecium algarvicum W.E.Nicholson & Dixon was discovered in Tunisia, which constitutes the first report of this Macaronesian-oceanic species in Africa. Three distinct populations were observed in ravines in the humid Meso-Mediterranean vegetation belt of Kroumiria. The Tunisian material is fully described, with particular attention to alar and supra-alar cells, prorate cells and other morphological characteristics. The density and size of the prorate cells appear to be a robust diagnostic characteristic for the separation of Isothecium algarvicum, I. alopecuroides and I. myosuroides. Detailed analysis of the forest habitat reveals a uniquely rich environment. The origin of a possibly relict species with Macaronesian-oceanic affinities is discussed.