Our commonest quillwort, widespread in shallow water (from almost emergent to more than one meter depth) in ponds, lakes and slow-moving rivers with nutrient poor, acidic, sandy or gravelly bottoms.

The North American subspecies of this cosmopolitan species is ssp. muricata (Durieu) Á. Löve & D. Löve. The leaves of this diploid (2n = 22) species are narrow, flexible, and bright green to yellow green. The megaspores are small (up to 0.55 mm in diameter); the ornamentation makes them appear spiky (like a miniature medieval mace) under high power in a dissecting microscope or through a 10× hand lens.

The rare hybrid Isoetes × hickeyi W. C. Taylor & N. T. Luebke (I. echinospora × I. lacustris) has been collected in Alger and Gogebic Cos.