Helianthus decapetalus |
Helianthus nuttallii |
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hélianthe à dix rayons, thin-leaf sunflower |
hélianthe de Nuttall, Nuttall's sunflower |
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Habit | Perennials, 60–200 cm (rhizomatous). | Perennials, 100–400 cm (rhizomatous). | ||||||||
Stems | erect, glabrous. |
(usually yellow-brown or greenish, sometimes glaucous) erect, glabrous, hispid, ± hirsute, or scabrous. |
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Leaves | 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; all or mostly opposite to mostly alternate; petioles 0.5–1.5 cm; blades light to dark green, 3-nerved (distal to bases) ± lanceolate to ± ovate, 4–20 × 0.8–4 cm, bases cuneate, margins entire or ± serrate (flat), abaxial faces hispid to hispidulous or tomentulose to villous-tomentose, gland-dotted. |
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Peduncles | 2–12 cm (not gland-dotted). |
1–18 cm. |
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Involucres | hemispheric, 10–20 mm diam. |
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Ray florets | 8–12; laminae 20–25 mm. |
10–21; laminae 20–25 mm (abaxial faces not gland-dotted). |
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Disc florets | 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 5–7 mm, lobes yellow; anthers dark brown to black, appendages yellow. |
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Phyllaries | 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. |
30–38 (loose, spreading), lanceolate to lance-ovate, 8–16 × 1.5–3 mm, (margins ciliate) apices acute to acuminate, abaxial faces usually ± strigose, rarely glabrate, not gland-dotted. |
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Heads | 3–6(–10). |
1–6. |
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Cypselae | 3.5–5 mm; pappi of 2 aristate scales 3–4 mm. |
3–5 mm, glabrate; pappi of 2 aristate scales 2.2–4.5 mm plus 0–2 lanceolate scales 0.5–1 mm. |
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Invo | -lucres hemispheric, 12–25 mm diam. |
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Paleae | 8–10 mm, 3-toothed. |
8–12 mm, 3-toothed. |
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2n | = 34, 68. |
= 34 (subspecies unknown). |
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Helianthus decapetalus |
Helianthus nuttallii |
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Phenology | Flowering summer–fall. | |||||||||
Habitat | Mesic to wet woodland edges | |||||||||
Elevation | 10–1200 m (0–3900 ft) | |||||||||
Distribution |
AL; AR; CT; DC; DE; GA; IA; IL; IN; KY; LA; MA; MD; ME; MI; MO; MS; NC; NH; NJ; NY; OH; OK; PA; RI; SC; TN; VA; VT; WI; WV; NB; ON; QC
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AZ; CA; CO; IA; ID; KS; MN; MO; MT; ND; NE; NM; NV; OK; OR; SD; UT; WA; WY; AB; BC; MB; ON; QC; SK
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Discussion | 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.) |
Subspecies 3 (3 in the flora). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 21, p. 158. | FNA vol. 21, p. 166. | ||||||||
Parent taxa | Asteraceae > tribe Heliantheae > subtribe Helianthinae > Helianthus | Asteraceae > tribe Heliantheae > subtribe Helianthinae > Helianthus | ||||||||
Sibling taxa | ||||||||||
Subordinate taxa | ||||||||||
Synonyms | H. trachelifolius | |||||||||
Name authority | Linnaeus: Sp. Pl. 2: 905. (1753) | Torrey & A. Gray: Fl. N. Amer. 2: 324. (1842) | ||||||||
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