Helianthus decapetalus
Helianthus strumosus
hélianthe à dix rayons, thin-leaf sunflower
hélianthe scrofuleux, pale-leaf sunflower, paleleaf woodland sunflower, rough sunflower, rough-leaf sunflower
erect, glabrous.
erect, glabrous or glabrate.
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.
cauline; mostly opposite, sometimes alternate (distal);
petioles 1–3 cm;
blades (light to dark green, 3-nerved distal to bases) lanceolate to lance-ovate or ovate, 7–18 × 2–10 cm, bases subcordate to ± cuneate, margins entire to ± serrate, abaxial faces glabrous or tomentulose, usually densely gland-dotted.
2–12 cm (not gland-dotted).
1–9 cm.
cylindric to hemispheric, 8–20 mm diam.
8–12;
laminae 20–25 mm.
10–20;
laminae ca. 12–20(–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.
35+;
corollas 5.5–6.5 mm, lobes yellow;
anthers dark, appendages dark or reddish brown.
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.
18–25 (erect, loose, or squarrose), lanceolate, 5.5–10 × 1.5–3 mm (equaling or slightly surpassing discs), (margins usually ciliate) apices acute to acuminate, abaxial faces glabrous or hispidulous, usually not gland-dotted.
3–6(–10).
3–15.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
4–5.5 mm, glabrate;
pappi of 2 aristate scales (1–)2–2.5 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
5.3–6.5 mm, 3-toothed.
= 34, 68.
= 68, 102.
Helianthus decapetalus
Helianthus strumosus
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 strumosus is variable, particularly for leaf shape and indument; sufficient study has not been undertaken to evaluate whether regional forms deserve taxonomic recognition. Hybridization with other polyploids, including H. decapetalus, H. hirsutus, and H. tuberosus, further complicates the situation. It differs from H. tuberosus in having glabrous (or glabrate) stems and in lacking tubers.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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