Helianthus decapetalus
Helianthus tuberosus
hélianthe à dix rayons, thin-leaf sunflower
girasole, Jerusalem artichoke, Jerusalem sunflower, topinambour, tuberous sunflower
erect, glabrous.
erect, scabro-hispid to hirsute (sometimes glaucous).
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; opposite or alternate proximally, usually alternate distally;
petioles 2–8 cm (often ± winged);
blades (3-nerved from near bases) lanceolate to ovate, 10–23 × 7–15 cm, bases broadly to narrowly cuneate, margins entire or serrate (flat), abaxial faces puberulent or hirsutulous to tomentulose and gland-dotted (abaxial) or ± scabrous (adaxial).
2–12 cm (not gland-dotted).
1–15 cm.
hemispheric, (10–25 ×) 8–12 mm.
8–12;
laminae 20–25 mm.
10–20;
laminae 25–40 mm.
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
60+;
corollas 6–7 mm, lobes yellow;
anthers dark brown or black, appendages dark or yellowish.
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.
(often dark green, drying nearly black) 22–35 (bases appressed, apices ± spreading, sometimes reflexed in fruit), lanceolate, 8.5–15 × 2–4 mm (subequal), (margins ciliate) apices acuminate, abaxial faces hispidulous or puberulent, gland-dotted.
3–6(–10).
3–15.
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
5–7 mm, glabrous or distally hairy;
pappi of 2 aristate scales 1.9–3 mm plus 0–1 deltate scales 0.5–0.8 mm.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
8–9 mm, 3-toothed (apices hairy).
= 34, 68.
= 102.
Helianthus decapetalus
Helianthus tuberosus
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 tuberosus is variable, probably in part stemming from hybridization with other polyploids, including H. pauciflorus, H. resinosus, and H. strumosus. Helianthus tuberosus is so widely spread as a weedy species that its original distribution is difficult to discern. It has been used as a food plant for its tubers by native Americans (although not necessarily domesticated or even cultivated); it has been developed as a crop primarily in Europe, where it has become widely naturalized. The common name Jerusalem artichoke is a misnomer, as explained by C. B. Heiser (1976).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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