Sp. Pl. 2: 903. 1753

Gen. Pl. ed. 5, 384. 1754

Etymology: Greek tetra, four, gonio, angle, and theca, container, alluding to quadrangular involucres
Treatment appears in FNA Volume 21. Treatment on page 178. Mentioned on page 176.
Perennials, mostly 30–120 cm. Stems erect. Leaves basal and/or cauline; mostly opposite; petiolate, subpetiolate, or sessile (bases sometimes connate-perfoliate); blades lanceolate, ovate, rhombic, or rounded-deltate, sometimes pinnatifid, ultimate margins usually toothed, faces glabrate, sparsely hispidulous, or puberulent, gland-dotted. Heads radiate, borne singly or in loose, corymbiform arrays. Involucres obpyramidal to hemispheric, 12–25+ mm diam. Phyllaries persistent, 10–25+ in ± 2 series (outer 4 broadly lanceolate, foliaceous, the inner ovate to lanceolate, smaller, more scarious, each subtending a ray floret). Receptacles conic, paleate (paleae persistent, lanceolate to lance-ovate, flat or weakly conduplicate, apices acute). Ray florets 6–21+, pistillate, fertile; corollas yellow (often with reddish nerves). Disc florets 25–150+, bisexual, fertile; corollas yellow, tubes (basally dilated) much shorter than ampliate, cylindric throats, lobes 5, deltate. Cypselae ± ovoid or plumply 4- or 5-angled, finely 32–40-ribbed, sparsely strigose or glabrous; pappi 0, or of 1–10+ subulate to acerose scales (to 0.5 mm), or of 16–30, ± spatulate scales (0.5–2 mm). x = 17.


s United States, n Mexico.


Species 4 (4 in the flora).


1 Pappi of 16–30, ± obovate to spatulate scales 0.5–2 mm > 2
1 Pappi 0, or of 1–10+ subulate to acerose scales to 0.5 mm > 3
2 Leaves mostly cauline (distal connate-perfoliate); ray florets 12–13, laminae 8–18 mm Tetragonotheca ludoviciana
2 Leaves mostly basal (cauline much smaller, none connate-perfoliate); ray florets 16–21+, laminae 20–30+ mm Tetragonotheca repanda
3 Stems sparsely tomentulose or glabrous (nodes usually auriculate-appendaged); ray laminae 10–18 mm; cypselae ± quadrate, 2.5–4 mm Tetragonotheca texana
3 Stems patently to retrorsely ± villous; ray laminae 20–40+ mm; cypselae ± ovoid, 4–6 mm Tetragonotheca helianthoides