Stems slender, branched, wiry, ± pilose, creeping, rooting; plant forming patches up to ± 4 dm. diam. Lvs mostly clustered at nodes; petioles slender, ± pilose, 1-2 cm. long; sheaths scarious, ± 5 mm. long, us. pilose. Lamina of narrow-obovate order, membr., clad in soft hairs to almost glab.; ± 3-5 cm. × 5-10 mm. (shade forms may be much longer, insolated much smaller); pinnate in lower part, pinnatisect to pinnatifid in upper; costa narrow, flat, ± pilose. Pinnae 8-15 pairs; mid-pinnae up to c. 5 mm. long, upper margins deeply incised, teeth triangular, acute, apiculate, up to 1∙5 mm. long; lower margins curved, us. entire. Lowest pinnae minute, narrow. Scapes of very diverse lengths, ranging from 10-75 mm. long, slender, with delicate spreading hairs, nude; receptacle slightly convex. Capitula of ♂ 4-5 mm. diam.; phyll. few in 2 series, broadly obovate-oblong, ± purple-tipped and -margined, silky outside, scarious. Capitula of ♀ 6-9 mm. diam.; phyll. in 3-4 series, c. 3 mm. long, broad, obtuse, silky, purple-margined, incurved over eglandular florets. ♀ ∞, with ovoid corolla, much-constricted at minutely 4-toothed apex; ♂ funnelform, minutely 4-toothed. Achenes ± curved, obconic, glab., grooved, almost subtrigonous.

A creeping, rapid-growing perennial herb, us. intermingled with other species in a turf, sts in patches colonising sand. Rhizomes at or near soil surface, green or dark, flexible, pilose, becoming pale, wiry and glabrous if buried; branches us. single at flowering nodes; leaves in two rows, single at the apex, 0.5-3.0 cm apart. Short shoots alternate on both sides of the rhizome, with 3-8 clustered leaves, under favourable conditions converted into rhizomes with distant leaves. Roots slender and weak, up to 0.8 mm diam. Leaves 1-pinnatifid, 0.5-10.0 × 0.3-2.0 cm; blade; 0.4-6.0 cm, elliptic or obovate, membranous (fleshy on coastal cliffs), bright green and often with brown pigment especially on proximal pinnae, us. sparsely pilose but glabrous to moderately pilose, midrib raised along most of ventral surface; pinnae 6-20 pairs, oblong to elliptic, often falcate, either all equidistant, not overlapping and cut to rhachis or (in subsp. squalida) distal pinnae closer and overlapping and not quite cut to rhachis; teeth us. present on larger pinnae at least, up to 10 per pinna, on distal margins, cut 1/3—2/3 across pinna, oblong, acute or acuminate. Peduncles us. borne on rhizomes, longer than leaves, 1-6 cm, nude or with 1 simple bract, sparsely pilose. Dioecious. Pistillate heads 3-5 mm, ca. 10 mm in fruit; surface convex; involucre urceolate; phyllaries 15-40 in 3 or more subequal rows, broadly elliptic, green, ± villous, with a broad brown-tipped scarious margin; inner phyllaries grow after anthesis to enclose subglobose fruiting head; florets 15—70, ca. 2.25 mm long, curved, yellow-green; corolla slightly longer than wide, with unequal teeth. Staminate heads 4-7 mm diam.; involucre hemispherical; phyllaries 5-10 in 1-2 rows, not growing after anthesis; florets slightly more numerous. Achenes up to 1.9 × 0.9 mm, slightly compressed, in section almost round or irregularly angled, with a pale unwrinkled papery surface turning brown and smooth. Flowers in spring and summer.