Clarifying the nomenclature of some Euro-Mediterranean quillworts (Isoetes, Isoetaceae): Indicator species and species of conservation concern

To stabilize the application of some names in the genus Isoetes in the Mediterranean biodiversity hotspot, we studied herbarium specimens and imaged spores with scanning electron microscopy, with special reference to those taxa in the I. longissima and I. histrix groups that were described from France, Algeria and Turkey, and are in need of a taxonomic revision. The following names are lectotypified: I. adspersa, I. boryana, I. delalandei, and I. viollaei. Holotypes of I. perralderiana and I. olympica were ascertained. We conclude that I. boryana (listed in the “Bern Convention” and in the European Union “Habitats” Directive) justifies consideration at species rank, but I. adspersa should be synonymized with I. longissima. Isoetes tenuissima and I. perralderiana are proposed as distinct species pending further studies. In the I. histrix group, we tentatively accept I. delalandei as a species, presenting some observations on “I. histrix f. subinermis” nom. nud. The latter might also represent a distinct species.