Annual herb with a slender taproot (sometimes woody at the base in grazed-off plants with secondary growth), (12) 20–70 cm. tall, simple or with several stems from about the base and sometimes branched above with branches diverging at 45 degrees or less. Stem and branches terete, striate, very slender, thinly pilose above especially at the nodes, rapidly glabrescent. Leaves narrowly linear, 15–75 × 0.5–4.5 mm., sparingly pilose when young, the upper folded inwardly, the lower frequently flat, all with a sharp, acute mucro up to 0.75 mm. long; axillary sterile, fasciculiform short shoots frequently present, occasionally with solitary abortive flowers. Inflorescence white or pinkish, considerably lengthening, 1.5–20 × 1.2–1.75 cm., the axis densely white-lanate, formed of numerous densely set partial inflorescences comprising generally four fertile flowers, two central and solitary, the others set on each side of one of these and subtended by a modified sterile flower on each side, partial inflorescences falling as a unit in fruit, the persistent bracts deflexed. Bracts ovate-acuminate, 3.5–5 mm. long, furnished with flexuose white hairs, deflexed after fruit-fall, brownish-aristate with the excurrent green or brownish midrib. Bracteoles of the partial inflorescences broadly deltoid-ovate, 4–6 mm., hyaline, dorsally long-pilose along the darker midrib, which is excurrent in a rigid mucro; bracteoles of secondary triads more narrowly deltoid-ovate, c. 5–8 mm. long, dorsally long-pilose and sharply aristate; bracteoles of sterile flowers similar but narrower and slightly more longly aristate; all bracteoles more rigid and accrescent (the longest to 10 mm. long or more) in fruit. Sterile flowers of mostly two broad-based spine-like processes finally c. 4–8 mm. long, some shorter processes sometimes found. Outer 2 tepals of fertile flowers narrowly oblong, c. 5–7 mm. long, hyaline except for a narrow central, 3-veined vitta, the 2 lateral veins joining the midrib below the apex, densely pilose over most of the central dorsal surface, midrib excurrent in a short, sharp mucro; inner 3 tepals somewhat shorter and narrower; all tepals somewhat sinuose in outline. Ovary turbinate, c. 1.5 mm. long; style slender, c. 3–4 mm. long, slender, glabrous, white or pinkish. Stamens c. 4–6 mm. long, filaments white or pinkish; anthers shortly oblong, c. 1 mm. Fruit ovoid, densely pilose over the dome-like apex, gibbous unilaterally with an acute horn-like process near the style, c. 2–2.5 mm. long; seed brown, smooth and shining, c. 1.75–2.25 mm. long, very feebly reticulate, only slightly compressed.
