Isothecium algarvicum W. E. Nicholson & Dixon, was discovered in Tunisia, which constitutes the first report of this Macaronesianoceanic 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.

To measure density and size of the prorate cells, we studied three species of Isothecium: I. algarvicum, I. alopecuroides and I. myosuroides (Table 1). Five leaves were dissected from each of five randomly chosen stems of each specimen, and measurements were made at 100 μm from the leaf apex in an area of ca 78 × 78 μm. For I. myosuroides, given the length of the leaf acumen, we took measurements where an area of 78 × 78 μm was reached.

Table 1. Provenance of the specimens used for the measurements of density and size of prorate cells.

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