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.

Distribution

s United States, n Mexico.

Discussion

Species 4 (4 in the flora).

Selected References

None.

Lower Taxa

Tetragonotheca helianthoides, Tetragonotheca ludoviciana, Tetragonotheca repanda, Tetragonotheca texana

Key

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