2n = 42

Slender suffruticose perennial with dark brown subterranean stems < 2 mm diam. Branches prostrate and < 50 cm long, or erect and < 5 cm long, c. 0.7 mm diam., brown, hirsute, epidermis flaking with age; internodes < 3.5 cm long on prostrate stems. Leaves hairy; stipules 2-6 mm long, margins, tips and abaxial face hairy, free portion linear, entire or bifid, < sheath; leaflets 3 or 4 pairs, the distal leaflet and 2 upper pairs obovate to suborbicular in outline, truncate at apex, shallowly cuneate at base, 2-10 × 2-6 mm; upper surface dull green, glabrous, smooth, with secondary venation indistinct; lower surface pale, glaucescent, the veins with appressed hairs; teeth 7-9 with margins thickened and recurved, hydathodes pink. Basal leaflet pairs less than lh the size of the penultimate pair, or linear and smaller than stipule lobes. Hairs simple, unicellular, < 1.5 mm long, on stipules, rachis and leaflets. Scapes terminal on short shoots, 4-13 cm long at flowering, hardly elongating as fruit matures, c. 0.5 mm diam., moderately hairy, pale brown. Scape bract linear or foliose, occasionally subtending a single floret. Capitulum 4-6 mm diam. at flowering, 10-15 mm diam. (including spines) at fruiting. Bracteoles on receptacle linear, c. 3 mm long, with hairy margins. Florets c. 40-50, minutely stipitate. Hypanthium c. 1 mm long, enclosing perigynous ovary, densely hairy, bearing 4 barbed spines which reach above the hypanthium rim. Sepals 4, arising from hypanthium rim, shortly joined at base, c. 1.5 mm long, elliptic, narrowed and thickened at tip, sparsely hairy on abaxial face. Petals 0. Stamens 2; filaments unequal, up to 2 mm long; anthers 0.3 × 0.5 mm, white. Style 1, 1.5 mm long, including white, fimbriate stigma 0.6 mm broad and protruding from aperture of hypanthium. Fruit indehiscent with a single achene enclosed in the hypanthium, obconic, c. 2 × 1.2 mm, brown, moderately hairy, 4-ribbed; spines 1 per rib, slender, 4-6 mm long, pale rose or brown, bearing a single rank of translucent, retrorse barbs at tip.

Suffrutex tenuis; caules c. 0.7 mm diam., ad 50 cm longi; proni et radicantes. Folia ad 5 cm longa, imparipinnata; foliola 7-9, foliola distalia quinque obovata vel suborbiculata, supra viridia, laevia, subtus pallida, sericea, dentibus crenatis et politis; stipuli integri vel befidi. Scapus c. 10 cm longus. Stylus albus. Antherae albae. Fructus c. 2 × 1.5 mm, pilosus. Inter species sectionis Ancistrum bene evolutis glochideis fructus spinis carpelloque singulari. Differt a A. anserinifolia foliorum forma, crenis, stipulis integris, fructibus minoribus.