304. Tetragonotheca Linnaeus, Sp. Pl. 2: 903. 1753; Gen. Pl. ed. 5, 384. 1754.
[Greek tetra, four, gonio, angle, and theca, container, alluding to quadrangular involucres]
John L. Strother
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.
Species 4 (4 in the flora): s United States, n Mexico.
Turner, B. L. and D. Dawson. 1980. Taxonomy of Tetragonotheca (Asteraceae–Heliantheae). Sida 8: 296–303.