Helianthus decapetalus
Helianthus silphioides
hélianthe à dix rayons, thin-leaf sunflower
Ozark sunflower, rosinweed sunflower
erect, glabrous.
erect, hispid to strigoso-hispid proximally, glabrate distally.
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.
basal and cauline; mostly opposite;
petioles 0.1–5.5 cm;
blades ovate to broadly ovate or suborbiculate, 7–15 × 4.5–15 cm, bases rounded to truncate or ± cuneate, margins entire or crenate to serrate, abaxial faces usually scabrous, sometimes ± strigose (hairs on midribs to 1 mm), not gland-dotted (cauline 9+ pairs proximal to heads, smaller).
2–12 cm (not gland-dotted).
0.5–10 cm.
hemispheric, 10–20 mm diam.
8–12;
laminae 20–25 mm.
8–13;
laminae 15–20 mm (abaxial faces not 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.
75+;
corollas 6–7 mm, lobes reddish;
anthers dark, appendages dark (style branches yellow).
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.
16–23, oblong to obovate, 8–10 × 3–5 mm, (margins ciliolate) apices obtuse to acute, sometimes mucronate, abaxial faces glabrous or glabrate.
3–6(–10).
3–15+.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
3–4 mm, glabrous or distally puberulent;
pappi of 2 aristate scales 2.5–2.7 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
9–10 mm, entire or ± 3-toothed.
= 34, 68.
= 34.
Helianthus decapetalus
Helianthus silphioides
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.)
Similar to Helianthus atrorubens, H. silphioides is distinguished by shorter hairs (less than 2 mm) on stems proximally and on abaxial leaf midveins, and by petioles of basal leaves less than 1/2 lengths of blades and winged less than 1/2 their lengths. As befits the name, specimens of H. silphioides (and also H. atrorubens) are not infrequently misidentified as species of Silphium.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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