Clear-water quillwort swards formed by the northern European and montane Isoetes lacustris and Isoetes echinospora or by the very local endemics Isoetes tenuissima of central western France and Isoetes brochonii of the eastern Pyrenees. Associated species may include Lobelia dortmanna, Sparganium angustifolium, Littorella uniflora, Hippuris vulgaris.