Helianthus annuus
Helianthus paradoxus
common sunflower, hairy leaf sunflower, sunflower
Paradox sunflower, Pecos sunflower
erect, usually hispid.
erect, glabrous or ± hispid.
mostly cauline; mostly alternate;
petioles 2–20 cm;
blades lance-ovate to ovate, 10–40 × 5–40 cm, bases cuneate to subcordate or cordate, margins serrate, abaxial faces usually ± hispid, sometimes gland-dotted.
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.
2–20 cm.
12–18 cm.
hemispheric or broader, 15–40(–200+) mm diam.
hemispheric, 15–20 mm diam.
(13–)17–30(–100+);
laminae 25–50 mm.
12–20;
laminae 20–30 mm.
150+(–1000+);
corollas 5–8 mm (throats ± bulbous at bases), lobes usually reddish, sometimes yellow;
anthers brownish to black, appendages yellow or dark (style branches yellow).
50+;
corollas 5–5.5 mm, lobes reddish;
anthers dark, appendages yellowish or dark (style branches reddish).
20–30(–100+), ovate to lance-ovate, 13–25 × (3–)5–8 mm, (margins usually ciliate) apices abruptly narrowed, long-acuminate, abaxial faces usually hirsute to hispid, rarely glabrate or glabrous, usually gland-dotted.
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.
1–9.
1–5.
(3–)4–5(–15) mm, glabrate;
pappi of 2 lanceolate scales 2–3.5 mm plus 0–4 obtuse scales 0.5–1 mm.
3–4 mm, glabrous;
pappi of 2 lanceolate scales 2.5–2.9 mm.
9–11 mm, 3-toothed (middle teeth long-acuminate, glabrous or hispid).
8–9 mm, apices 3-toothed (apices glabrous).
= 34.
= 34.
Helianthus annuus
Helianthus paradoxus
Helianthus annuus is widely distributed, including weedy, cultivated, and escaped plants. It is the only native North American species to become a major agronomic crop. Despite its considerable variability, attempts have failed to produce a widely adopted infraspecific system of classification. Forms with red-colored ray laminae, known from cultivation and occasionally seen escaped, trace their ancestry to a single original mutant plant. It hybridizes with many of the other annual species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Of conservation concern.
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).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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SW CO Wildflowers, Turner Photog. 
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