Annuals, 130-200 cm. Stems erect, glabrous or ± hispid. Leaves mostly cauline; opposite (proximal) or mostly alternate; petioles 1.5-6 cm; blades lanceolate to lance-ovate, 7-17.5 × 1.7-8.5 cm, bases cuneate, margins entire or (larger leaves) toothed, abaxial faces ± scabrous, not gland-dotted. Heads 1-5. Peduncles 12-18 cm. Involucres hemispheric, 15-20 mm diam. Phyllaries 15-25, lanceolate to lance-ovate, 6-19 × 0.7-4 mm (equaling or slightly surpassing discs), (margins ciliate) apices (spreading to recurved) acuminate, abaxial faces usually glabrate or sparsely hispid. Paleae 8-9 mm, apices 3-toothed (apices glabrous). Ray florets 12-20; laminae 20-30 mm. Disc florets 50+; corollas 5-5.5 mm, lobes reddish; anthers dark, appendages yellowish or dark (style branches reddish). Cypselae 3-4 mm, glabrous; pappi of 2 lanceolate scales 2.5-2.9 mm. 2n = 34. Flowering late summer-fall. Saturated saline soils, desert wetlands; of conservation concern; 1000-1200 m; N.Mex., Tex. Helianthus paradoxus is listed by the U.S. Fish and Wildlife Service as an endangered species and is in the Center for Plant Conservation´s National Collection of Endangered Plants. It is of hybrid origin; the parents are H.annuus and H. petiolaris (L. H. Rieseberg et al. 1990). It occupies a different habitat type than either parent (H. annuus usually on clay-based mesic soils and H. petiolaris usually on dry, sandy soils).