Stems freely branched, to 2.5 m, lvs to 1 m, with 3-7 strong nerves and many minute ones, on sterile stems to 1 cm wide, on fertile ones 2-5 mm wide; lf-sheaths closed, splitting in age; spadix 2-8 cm, lacking retinacula; frs ±exserted, the body 3-4 mm, the beak 1-2 mm; seed strongly ca 20-ribbed, the ribs visible through the pericarp; 2n=12. Shallow water (to 10 m) in sheltered bays and coves, usually wholly submersed; circumboreal, on the Atlantic coast from Greenl. to Fla. (Z. stenophylla)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.