Helianthus decapetalus
Helianthus microcephalus
hélianthe à dix rayons, thin-leaf sunflower
small woodland sunflower, small-head sunflower, woodland sunflower
erect, glabrous.
erect, glabrous.
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; opposite or alternate;
petioles 0.3–3 cm;
blades (greenish, at least abaxially, 3-nerved at bases) lanceolate, 7.2–15.5 × 1.3–4 cm, bases cuneate, margins entire or serrate, abaxial faces tomentulose, densely gland-dotted.
2–12 cm (not gland-dotted).
1–3(–8) cm.
cylindric, 5–7 mm diam.
8–12;
laminae 20–25 mm.
5–8;
laminae 10–14 mm.
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
15–22;
corollas 4–5.5 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.
12–17, lance-linear, 3–6.5 × 1.5–2.5 mm, (margins ciliate) apices acuminate, abaxial faces glabrate, not gland-dotted.
3–6(–10).
(1–)3–15+.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
3.5–4.2 mm, glabrous;
pappi of 2 aristate scales 1.5–2.2 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
5–7 mm, 3-toothed (apices hairy).
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus microcephalus
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 microcephalus is distinguished by its relatively small heads, which have relatively few phyllaries, ray florets, and disc florets, as well as the usually tomentulose abaxial faces of the leaves. Hybrids with H. divaricatus are known.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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