Helianthus debilis
Helianthus paradoxus
cucumberleaf sunflower, weak sunflower
Paradox sunflower, Pecos sunflower
decumbent to erect, glabrous, hirsute, or puberulent.
erect, glabrous or ± hispid.
mostly cauline; mostly alternate;
petioles 1–7 cm;
blades deltate-ovate, lance-ovate, or ovate, 2.5–14 × 1.8–13 cm, bases cordate to truncate or broadly cuneate, margins subentire to serrate, abaxial faces glabrate to hispid, not 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.
9–50 cm.
12–18 cm.
hemispheric, 10–22 mm diam.
hemispheric, 15–20 mm diam.
11–20;
laminae 12–23 mm.
12–20;
laminae 20–30 mm.
30+;
corollas 4.5–5 mm, lobes usually reddish, sometimes yellow;
anthers dark, appendages dark (style branches usually reddish, rarely yellow).
50+;
corollas 5–5.5 mm, lobes reddish;
anthers dark, appendages yellowish or dark (style branches reddish).
20–30, lanceolate, 8–17 × 1–3 mm, apices acute to long-attenuate, abaxial faces glabrous or ± hispid, not 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.
1–3.
1–5.
2.5–3.2 mm, glabrous or sparsely hairy;
pappi of 2 lanceolate or lance-linear scales 1.2–2.5 mm.
3–4 mm, glabrous;
pappi of 2 lanceolate scales 2.5–2.9 mm.
7.5–8 mm, apices 3-toothed (middle teeth acuminate, usually glabrous or hispid, sometimes ± villous or bearded).
8–9 mm, apices 3-toothed (apices glabrous).
= 34.
Helianthus debilis
Helianthus paradoxus
Subspecies 5 (5 in the flora).
C. B. Heiser (1956) placed 8 subspecies in Helianthus debilis; he noted that alternative taxonomic treatments might recognize these in as many as three species, or expand the single species to include H. petiolaris. Later, Heiser et al. (1969) separated three of the subspecies as H. praecox. Isozyme data (R. P. Wain 1982, 1983; L. H. Rieseberg and M. F. Doyle 1989) show that all are closely related. Documented hybridization with H. annuus further complicates the situation. The treatment by Heiser et al. is followed here.
Helianthus debilis is adventive beyond the Atlantic and Gulf coasts of the United States.
(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.)
1. Stems decumbent; peduncles 9–20(–22) cm | → 2 |
1. Stems erect; peduncles (15–)20–50 cm | → 3 |
2. Stems glabrous or puberulent; leaf blades serrulate or shallowly, regularly serrate, abaxial faces sparsely, if at all, gland-dotted | subsp. debilis |
2. Stems hirsute; leaf blades deeply, irregularly serrate, abaxial faces densely gland-dotted | subsp. vestitus |
3. Leaves 8–14 cm; peduncles (relatively slender) 20–40 cm; discs 10–15(–17) mm diam | subsp. silvestris |
3. Leaves 2.5–9 cm; peduncles (not notably slender) 10–50 cm; discs 14–20 mm diam | → 4 |
4. Leaf blades usually deeply, irregularly serrate; peduncles 10–25(–30) cm; ray lami-nae 12–20(–22) mm | subsp. tardiflorus |
4. Leaf blades usually shallowly, regularly serrate; peduncles 25–50 cm; ray laminae (15–)20–23 mm | subsp. cucumerifolius |
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