Perennial herb 0.4–0.9 m tall, erect or decumbent and rooting at the nodes and sending up erect leafy branches; stems often reddish, winged or with interrupted wings, glabrous; wings 1–3 mm wide, entire or dentate. Leaves aromatic, narrowly elliptic to almost linear, 1–13 cm long, 0.1–1.3 cm wide, base decurrent, margins denticulate or subentire, apex acute or obtuse, glabrous or rarely sparsely puberulous along midrib and margins, glandular-punctate. Glomerules purple or mauve (rarely white), globose to ovoid, 7–15 mm long, 7–10 mm in diameter; peduncles 1–11 cm long, with or without very narrow wings; receptacle orbicular to ellipsoid; glomerule bracts hidden (apart from the apex) except for the lowermost in the early stages, ovate to obovate, 2.5–4 mm long, margins ciliate, apex apiculate, puberulous; capitula sessile, with 2–4 bracts, the laterals folded, cuneiform, 2–3 mm long, scarious, apiculate, distally papillose. Florets: outer florets 4(–6), tube narrowing from a slightly inflated and corky base, 1.3–1.6 mm long (only occasionally in var. randii, never in var. bibracteata), or more often cylindrical, 1.7–2.5 mm long, lobes 0.1(–0.3) mm long; style 2.5–3 mm long or more often included and invisible; inner florets (1–)2, tube widening from a narrow base, glandular and corky, constricted just below the lobes, 0.9–1.7 mm long, lobes glandular, 0.3–0.4 mm long, anthers 0.9–1.2 mm long, style 1.5–2.2 mm long, entire or minutely bifid. Achenes of outer florets narrowly ellipsoid, 1–1.2 mm long, puberulous and glandular, of inner florets glabrous, ?sterile.
