Helianthus decapetalus
Helianthus deserticola
hélianthe à dix rayons, thin-leaf sunflower
desert sunflower
erect, glabrous.
(green or red) erect, densely hirsute and gland-dotted.
cauline; opposite (proximal or all) or alternate (distal);
petioles (1–)2–5 cm;
blades (green, 3-nerved distal to bases) lanceolate to ovate, 7–21 × 4–10 cm, bases rounded to cuneate (often shortly decurrent onto petioles), margins usually serrate (moderately to notably in larger leaves), abaxial faces ± scabro-hispidulous, relatively sparsely gland-dotted.
mostly cauline; mostly alternate;
petioles 1–6 cm;
blades lanceolate to lance-ovate, 2.5–5 × 1–2 cm, bases cuneate, margins entire, abaxial faces hispid-hirsute, densely gland-dotted.
2–12 cm (not gland-dotted).
1–3(–8) cm.
hemispheric, 13–25 mm diam.
8–12;
laminae 20–25 mm.
7–13;
laminae 10–30 mm (abaxial faces gland-dotted).
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
25+;
corollas 5.5–6 mm, lobes reddish;
anthers dark, appendages purplish (style branches reddish).
20–25 (often reflexed), lance-linear to lanceolate, 11–16 × 2–3 mm (sometimes leaflike, longest surpassing discs by 1/2+ their lengths), (margins ciliate) apices attenuate, abaxial faces strigillose to glabrate, not gland-dotted.
13–21, lanceolate to lance-ovate, 7–19 × 1.5–2 mm (equaling or slightly surpassing discs), (margins ciliate) apices acuminate, abaxial faces hispid (hairs erect, often 1+ mm) gland-dotted.
3–6(–10).
1–5.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
4–5 mm, pilose;
pappi usually of 2 linear scales 1.6–2.5 mm plus 4–6 linear or ovate, erose scales 0.5–1 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
8–9 mm, ± 3-toothed (middle teeth equaling or slightly surpassing discs, apices yellowish brown, usually hispid).
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus deserticola
Helianthus decapetalus is sometimes confused with Heliopsis helianthoides because of shared habitats and superficial similarities. The tetraploid cytotype of H. decapetalus intergrades (and apparently hybridizes) with H. strumosus, particularly in the southern Appalachians; individual specimens can be difficult to place in one or the other species. In addition to morphologic differences, H. decapetalus usually occurs in more mesic habitats, particularly along watercourses; H. strumosus is found in drier sites such as roadside slopes. Helianthus ×multiflorus Linnaeus is a sterile hybrid, often with “doubled” heads (in which disc florets are replaced by ray florets); it is cultivated and is sometimes included within H. decapetalus, e.g., H. decapetalus var. multiflorus (Linnaeus) A. Gray; its parents are H. decapetalus and H. annuus.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Helianthus deserticola is relatively uncommon; it is not federally listed. Abundant subsessile glands (“resin dots”) on stems, leaves, phyllaries, and abaxial faces of ray laminae help to distinguish H. deserticola from H. anomalus, with which it is sometimes lumped. L. H. Rieseberg (1991) demonstrated that it is of hybrid origin; parental species are H. annuus and H. petiolaris.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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