Perennial, shortly rhizomatous, greenish herb, (10-) 15-50 (-80) cm tall, erect to almost prostrate, sometimes rooting from the lower nodes, non-stoloniferaus; stem terete, faintly sulcate with 2-6 cauline leaves. Leaves shorter than stem linear transversely 15-25 septate-nodose, subterete, green, usually 1-2 mm broad; basal sheaths usually brownish, auricled. Inflorescence terminal, often richly and somewhat dichotomously branched, with many shortly stalked heads, each consisting of (4)6-10(-12) flowers, 5-10 mm across; lowest bract erect, usually c. half as long as the inflorescence, leafy. Flowers (2-)2.5-3 mm long, brownish to greenish, sessile; perianth segments lanceolate, acute inner subobtuse with broad whitish margins. Stamens 6, much shorter than the perianth, with anthers c. as long as the filaments. Capsules 34 mm long, 1.5-2 mm broad, oblong-ovoid or ellipsoid, usually contracted abruptly into a short beak, conspicuously exceeding the perianth, brownish to greenish, often lustrous, many seeded (3040); seeds c. 0.4(-0.5) mm long, ovoid or ellipsoid, brownish 2n=80.

Type: Habitat in Europe aquosis.

Distribution: Most of Europe, N. Africa, Central and S.W. Asia, to Pakistan and the Himalayas; eastern N. America; widely introduced reaching Australia and New Zealand.

A widely distributed and very variable species, known to have: (i) several ecotypes (Clapham et al, Fl.Brit. Isles 990, 1962); (ii) larger forms with 80 chromosomes and up to 18 flowers in each head; (iii) and hybrid, with sterile capsules and usually 3-6 flowers in each head.