Paradox Sunflower

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).

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.