A new species of Echinodorus subg. Helianthum, E. zombiensis Jérémie, represented by a population discovered in a lake located in the southern part of Basse-Terre (Guadeloupe, Lesser Antilles), is described and illustrated. Close to E. tenellus (Martius) Buchenau [= E. bolivianus (Rusby) Holm-Nielsen, syn. nov.], the new species is distinguished by macro-morphological, anatomical, palynological, cytogenetical and chemical characters of which suggest that speciation is probably still in progress and that differenciation is not yet complete. The genus Echinodorus was previously known in the Lesser Antilles only by a single species, E. berteroi (Sprengel) Fassett, belonging to the subg. Echinodorus.