Description from Flora of China
Alga marina (Linnaeus) Lamarck.
Rhizomes creeping, 2-4 mm in diam., with elongated internodes. Leaves on non-flowering shoots 5-8, linear, longer than 50 cm, 3-6 mm wide, 5-7-veined, margin entire, apex rounded or mucronate; sheaths closed, tubular, membranous, splitting irregularly when old; auricle ca. 1 mm; ligule ca. 0.5 mm; intravaginal squamules 2 or 4, linear. Flowering stems ca. 1 m, branched; spathes with flattened stalk, narrower than leaves; spadix without projections. Anthers 4-5 mm. Ovary 2-3 mm; style 1.5-2.5 mm; stigmas ca. 3 mm. Fruit ellipsoid, ca. 4 mm. Seeds longitudinally ribbed. Fl. and fr. Mar-Jul. 2n = 12.
On fine gravel, sand, or mud near low tide mark. Coasts of Hebei, Liaoning, Shandong [coasts of Japan, Korea, Myanmar, Russia, Thailand; N Africa, Europe, North America].