Helianthus decapetalus
Helianthus resinosus
hélianthe à dix rayons, thin-leaf sunflower
resindot sunflower
erect, glabrous.
(often reddish or purplish) erect, hirsute or villous.
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 0.5–2 cm (broadly winged);
blades lanceolate to ovate, 6.5–20 × 3.2–9 cm, bases gradually narrowed (onto petioles), margins entire or serrate, abaxial faces hirsute to tomentose, gland-dotted.
2–12 cm (not gland-dotted).
1–3 cm.
hemispheric, 15–27 mm diam.
8–12;
laminae 20–25 mm.
10–20;
laminae (often light yellow) 18–30 mm.
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
90+;
corollas 8–8.5 mm, lobes yellow;
anthers dark, appendages dark.
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.
20–30 (squarrose to reflexed, at least tips), lanceolate, 10–21 × 3–5 mm (notably surpassing discs), apices acute to attenuate, abaxial faces hispid to villous, densely gland-dotted (at least toward apices).
3–6(–10).
1–5.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
5–7 mm, glabrate;
pappi of 2 aristate scales 2.4–2.6 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
9–11 mm, 3-toothed (gland-dotted).
= 34, 68.
= 102.
Helianthus decapetalus
Helianthus resinosus
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.)
Consistent with its epithet, Helianthus resinosus has abundant subsessile glandular hairs (“resin dots”) on its leaves, phyllaries, paleae, and ray laminae. It intergrades and has been reported to hybridize with H. tuberosus. It is cultivated and usually sold under the long-misapplied name H. tomentosus Michaux.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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