Infl. a spadix or spike enclosed, at least at first, in a spathe-like If-sheath. Fls ∞, in 2 vertical rows on one surface of the flattened axis. Per. 0 or perhaps sts represented by a bract-like lobe (retinaculum). Stamen solitary; anthers sessile, dehiscence longitudinal; pollen thread-like. Carpel solitary, narrowing above to short style; stigmas 2, flagelliform; ovule solitary, pend. Achene ± beaked, indehiscent or bursting irregularly. Rhizomatous, glab., marine perennials with flattened stems and 2-ranked, linear, sheathing lvs. Two genera, monoec., widespread, dioec., from north Pacific coasts only.