Annual herb, usually up to 10 cm high but in temporarily swampy sites to 30 cm high; stems usually much branched, minutely scabridulous, with continuous wings up to 3 mm wide. Leaves subopposite, sessile, lanceolate, 2–5(–8) cm long, 0.4–1.5(–2.5) cm wide, base cuneate and decurrent, margins obscurely denticulate, apex acute with a spiny point, scabridulous and glandular on both surfaces. Capitula 7–10 mm long, solitary in leaf axils and branching points, sessile; phyllaries of two kinds, the outermost distally green and foliose, to 14 mm long and 4 mm wide, at anthesis spreading, the inner ones cream, ovate, 2–8 mm long, tapering to a spiny and outcurving tip, ciliate, glandular; receptacle with membranaceous paleae to 4 mm long, 3-lobed. Florets 10–12; outer florets with tube cylindric, 2–3.5 mm long, ray 2.5 mm long, 0.6–0.8 mm wide and glandular beneath, style 2.5–3.8 mm long; inner florets with tube cylindric and rather squat, 1–2.6 mm long, lobes 1.2–1.5 mm long and pilose and glandular, anthers 1.4–1.5 mm long, style 2.2–4 mm long. Achenes ellipsoid, 0.8–1.1 mm long, densely hairy; pappus of membranaceous scales, those of the inner series awned and to 2 mm long.