Abstract
A new benthic diatom species, Gomphonema vidalii sp. nov., is described with light (LM) and scanning electron microscopy (SEM) observations. It was found in three Mediterranean watercourses: Farfa (Central Italy), Bévéra (France and Italy) and Paillon streams (South-Eastern France). Valves have a clavate shape and striae are slightly radial, the central ones being shorter than the others; one stigma is present in the central area. G. vidalii belongs to the group of Gomphonema species with doubly-punctate striae, a feature which is considered by some authors typical of the genus Gomphoneis. Distinct to Gomphonema vidalii is the presence of stigmoid areolae in the central area, different in structure from stigmata and stigmoids which can be found in some Gomphonema and Gomphoneis species.