Annual or perennial strict erect herbs 15–60 cm. tall, with one to several unbranched stems from a short subterranean woody base; roots long, fibrous, occasionally with bead-like nodules; stems mostly glabrous to shortly pubescent at the base. Leaves (3)11–45(61) x 0.4–1.8(2) mm., narrowly linear to narrowly linear-lanceolate, rarely filiform, apex acute, slightly tapered to the base, ± scabrid above otherwise glabrous; stipular sheath (0.5)0.6–1.9(2.2) mm. long, glabrous, stipular lobes (0.3)0.9–3.5(4) mm. long. Inflorescences many-flowered with 5–12 flowered partial inflorescences capitate; peduncles (18)32–75(170) mm. long, glabrous. Calyx tube (1.4)1.6–2.8(3.2) x (1.1)1.3–2(2.4) mm., ovoid-elliptic, scabrid or ± glabrous; lobes (1.8)2–2.8(4) mm. long and 0.3–1.3(1.8) mm. wide at the base, narrowly triangular, glabrous. Flowers strongly scented in the afternoon and evening; corolla lobes above white, pinky white, cream, pale yellow or khaki yellow, tube and lobes beneath darker — usually olive green to brownish, glabrous or back of lobes scabridulous; tube often slightly bent, altogether (10.3)11–19.2(23.1) mm. long, the widened part (2.1)2.3–3.1(3.5) x 0.8–1.9(2.2) mm., the narrow part (0.3)0.5–1(1.2) mm. wide; lobes (3.9)4.4–8.5(8.8) x 0.9–2.7(3) mm., narrowly linear-elliptic to linear-oblong, parted to the base, ± acute. Anthers narrowly linear, c. 2–4 mm. long; pollen (3)4(5)-colporate. Style c. 3–5 mm. long; stigma lobes 1.5–3 mm. long. Capsules (2.1)2.4–3.2(3.9) x (3.1)3.4–4.2(4.8) mm., subglobose, glabrous. Seeds dark brown c. 0.8–1 mm. long, slightly flattened, ellipsoid.