First record of Sparganium oocarpum in Italy and new regional distribution data for Sparganium erectum species complex

The results of herbarium investigation of the species belonging to the Sparganium erectum group are here presented. The study was based on the revision of specimens with ripe fruits preserved in the Herbarium Centrale Italicum (FI) of the Natural History Museum of the University of Florence and other local herbaria. The presence of Sparganium oocarpum, not yet recorded in Italy, has been confirmed by the evaluation and measurement of important diagnostic characters (shape of the fruit, length, and width of the fruit, length of the peduncle, length of the style) and by their statistical analysis. Finally, a new identification key for the four species belonging to S. erectum group, based on the Italian herbarium material studied, is proposed.