Helianthus decapetalus
Asteraceae tribe Heliantheae subtribe Helianthinae
hélianthe à dix rayons, thin-leaf sunflower
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.
usually mostly cauline, rarely mostly basal; mostly opposite (distal often alternate) or mostly alternate, rarely whorled; petiolate or sessile;
blades (often 3- or 5-nerved) orbiculate or deltate to lanceolate or linear (and intermediate shapes), sometimes lobed, ultimate margins entire or toothed, faces usually hairy (often hispid to scabrellous), often gland-dotted.
2–12 cm (not gland-dotted).
cylindric to hemispheric or rotate.
usually flat or convex, sometimes hemispheric or conic, usually paleate (epaleate in Lagascea; paleae usually falling, sometimes persistent, mostly oblong to linear, often conduplicate, herbaceous to scarious, apices sometimes ± 3-lobed or -toothed; becoming hardened perigynia completely investing cypselae in Sclerocarpus).
8–12;
laminae 20–25 mm.
0 or 5–30(–100+), neuter, or styliferous and sterile;
corollas usually yellow to orange, sometimes partly or wholly brown to purple or red-brown to reddish.
40+;
corollas 6.5–7.2 mm, lobes yellow;
anthers usually dark brown to black (rarely reddish brown), appendages dark or reddish brown.
1 (Lagascea) or 10–200(–1000+), bisexual, fertile;
corollas usually yellow to orange, sometimes brown to purple or reddish to red-brown, tubes shorter than or about equaling cylindric or funnelform throats, lobes 5, ± deltate (equal);
anther thecae dark or pale;
stigmatic papillae usually continuous.
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.
persistent, 4–45(–100+) in 1–6+ series (usually distinct, ± connate in Lagascea, broadly ovate to linear, subequal or unequal).
0.
3–6(–10).
usually radiate, sometimes discoid, borne singly or in corymbiform (paniculiform or racemiform) arrays (glomerules or second-order heads of 1–2-flowered heads in Lagascea).
3.5–5 mm;
pappi of 2 aristate scales 3–4 mm.
often ± compressed, flattened, biconvex, clavate, columnar, obovoid, obpyramidal, or prismatic (lengths usually 1–2 times diams.), glabrous or hairy (faces and/or angles);
pappi 0, or (often readily falling or fragile, sometimes persistent) usually of (1–)2(–8+) (sometimes aristate) scales and/or awns, sometimes coroniform.
-lucres hemispheric, 12–25 mm diam.
8–10 mm, 3-toothed.
= 34, 68.
Helianthus decapetalus
Asteraceae tribe Heliantheae subtribe Helianthinae
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.)
Genera 17, species 363 (8 genera, 69 species, including 1 hybrid, in the flora).
Circumscription of Helianthinae adopted here (i.e., that of H. Robinson 1981) is narrower than traditional circumscriptions (e.g., T. F. Stuessy 1977[1978]), which included genera here treated in Ecliptinae, Galinsoginae, and Rudbeckiinae.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Phyllaries 4–5 in ± 1 series (connate); disc florets 1(–2; the 1–2-flowered heads aggregated in glomerules or second-order heads) | Lagascea |
1. Phyllaries 5–45(–100+) in (1–)2–6+ series (distinct); disc florets (10–)15–200(–1000+) | → 2 |
2. Receptacles paleate (each palea completely investing and falling with a cypsela, eachforming a hardened perigynium) | Sclerocarpus |
2. Receptacles paleate (paleae sometimes conduplicate, ± enfolding cypselae, not forming perigynia) | → 3 |
3. Heads borne singly (peduncles usually distally dilated, fistulose) | Tithonia |
3. Heads borne singly or in corymbiform, paniculiform, racemiform, or thyrsiform arrays (peduncles rarely, if ever, notably dilated or fistulose) | → 4 |
4. Cypselae flattened, thin-margined | Simsia |
4. Cypselae ± compressed, biconvex, or 3- or 4-angled, often obpyramidal | → 5 |
5. Cypselae glabrous or glabrate; pappi 0 | → 6 |
5. Cypselae usually ± strigose, sometimes glabrous or glabrate; pappi of 2–6+, persistent, readily falling, or tardily falling scales | → 8 |
6. Shrubs (leaves often lobed, lobes usually 3–9, ± linear) | Viguiera |
6. Annuals or perennials (leaves not lobed) | → 7 |
7. Annuals; leaf blades lanceolate to linear; involucres 5–6 mm diam.;phyllaries 11–17 | Helianthus |
7. Annuals or perennials; leaf blades lance-linear, lanceolate, ovate, rhombic, or rhombic-ovate; involucres 6–14 mm diam.; phyllaries14–25 | Heliomeris |
8. Shrubs; involucres 5–9 mm diam | Bahiopsis |
8. Annuals or perennials; involucres (5–)7–40+ mm diam | → 9 |
9. Pappi readily falling | Helianthus |
9. Pappi persistent or tardily falling | Viguiera |
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