Isoetes pedersenii, a new species from Southern South America

the name isoetes pedersenii h.p. fuchs (lycophyta), a species known only from the mburucuyá national park, corrientes, argentina, is validated. observations were carried out on herbarium material with stereoscopic, light and scanning electron microscopes. the species is described and typified. a diagnosis and discussion about its distribution and its relationship with the morphology of other species of isoetes are provided.