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Published In: Species Plantarum 2: 904. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 8/11/2017)
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Project Data     (Last Modified On 8/10/2009)

 

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79. Helianthus L. (sunflower)

(Heiser et al., 1969)

Plants annual or perennial herbs, the annuals with taproots, the perennials usually with rhizomes. Stems erect or ascending, unbranched or more commonly several-branched, mostly above the midpoint, with several longitudinal lines or ridges, variously glabrous to roughened or hairy. Leaves opposite and/or alternate, in a few species mostly basal, sessile or petiolate, the bases sometimes somewhat expanded and wrapping around the stem. Leaf blades simple, narrowly linear to nearly circular, tapered to shallowly cordate at the base, mostly tapered or less commonly broadly angled to a sharply pointed tip (rarely rounded), the margins entire to variously sharply toothed, the surfaces variously glabrous to roughened or hairy, sometimes also with scattered, sessile, spherical, yellow glands. Inflorescences most commonly panicles (sometimes few-flowered and appearing racemose) or in some species loose axillary clusters or of solitary axillary or terminal heads, the heads with short to more commonly relatively long, usually bractless stalks. Heads radiate. Involucre cup-shaped to broadly cup-shaped or somewhat bell-shaped, the bracts in mostly 2–4 unequal to subequal, overlapping series. Involucral bracts 12–40, variously narrowly lanceolate to ovate, ascending or with the tips loosely spreading, green with often hairy margins, the outer surface glabrous or more commonly variously roughened or hairy, often also with scattered, sessile, spherical, yellow glands, with 1 to several fine nerves. Receptacle flat to convex or slightly conical, usually not elongating as the fruits mature (occasionally broadening somewhat as the fruits mature), with chaffy bracts subtending the ray and disc florets, these somewhat concave and wrapped around the florets. Ray florets sterile (lacking stamens and style at flowering and with an ovary that is shorter and thinner than those of the disc florets, not developing into a fruit), the corolla showy, relatively broad, yellow (often pale yellow in H. decapetalus), not persistent at fruiting. Disc florets numerous, perfect, the corolla yellow or purple to reddish brown, not expanded at the base or persistent at fruiting (but often with a swollen portion toward the midpoint of the tube). Style branches with the sterile tip somewhat elongate and tapered. Pappus of the ray and disc florets of 2 short awns 1–5 mm long, sometimes also with 1–6 additional inconspicuous scales or awns 0.2–2.0 mm long, not persistent at fruiting. Fruits obovate to somewhat wedge-shaped in outline, somewhat flattened and often somewhat 4-angled in cross-section, the surface smooth or sometimes with several fine lines or nerves, glabrous or hairy, purplish black, sometimes with lighter mottling, usually not shiny. About 51 species, U.S., Canada, Mexico.

The sunflowers are a variable group, but most species are relatively easily recognized as members of the genus. Sometimes specimens of Helianthus are confused with Heliopsis (see the treatment of that genus for further discussion) or with Silphium (whose species tend to be more resinous and to have larger, broader involucral bracts). Within Helianthus, delimitation of particularly the perennial species is complicated by the presence of polyploidy and hybridization. Determination of specimens is complicated by the widespread incidence of hybridization among several of the common species, but in Missouri the hybrids generally are encountered as solitary or few individuals within populations of one or both putative parents. The exception to this rule is H. ×laetiflorus, which occasionally occurs as small populations separate from either parent. In the Ozarks, the main problems of species-level recognition appear to center around H. divaricatus, H. hirsutus, and H. strumosus, although smaller plants of H. tuberosus also can be problematic to identify. See the treatments of those species for further discussion.

 

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1 1. Leaves all or mostly alternate (sometimes appearing relatively crowded along the stem)

2 2. Leaf blades very narrow (mostly 7–20 times as long as wide), those of the largest leaves 0.1–1.0(–1.5) cm wide, linear to narrowly lanceolate

3 3. Leaves mostly narrowly lanceolate, folded longitudinally along the midvein at maturity but with relatively flat margins; disc florets with the corollas yellow ... 7. H. MAXIMILIANII

Helianthus
4 3. Leaves all or mostly linear, not folded longitudinally but with the margins curled under; disc florets with the corollas reddish brown to dark purple (at least the lobes and the upper portion of the tube)

5 4. Stems sparsely to moderately hairy, especially toward the base, not glaucous; plants with rhizomes absent or very short, not occurring as colonies of stems ... 1. H. ANGUSTIFOLIUS

Helianthus angustifolius
6 4. Stems glabrous and often somewhat glaucous; plants with long-creeping, branched rhizomes, often colonial ... 13. H. SALICIFOLIUS

Helianthus salicifolius
7 2. Leaf blades broad to moderately narrow (mostly 1.2–10.0 times as long as wide), those of the largest leaves 1–35 cm wide, lanceolate to broadly ovate-triangular

8 5. Plants annual, with taproots; disc florets with the corollas reddish brown to dark purple (at least the lobes and the upper portion of the tube); receptacle flat to slightly convex; largest leaves with the blade usually ovate to triangular-ovate or broadly ovate, less commonly oblong-lanceolate

9 6. Involucral bracts with relatively long, spreading hairs along the margins and often also on the outer surface; chaffy bracts with inconspicuous, short hairs toward the tip; fruits glabrous or more often densely and minutely hairy when young, but usually appearing glabrous or nearly so at maturity ... 2. H. ANNUUS

Helianthus annuus
10 6. Involucral bracts with minute, ascending to sometimes more or less spreading hairs along the margins and the outer surface; chaffy bracts with the middle lobe densely pubescent with conspicuous, white hairs at the tip; fruits usually persistently moderately short-hairy, at least along the margins ... 12. H. PETIOLARIS

Helianthus petiolaris
11 5. Plants perennial, with a coarse, sometimes woody rootstock and short to long rhizomes; disc florets with the corollas yellow; receptacle convex to short-conical; largest leaves with the blade usually lanceolate to narrowly oblong-elliptic or narrowly ovate

12 7. Stems glabrous below the midpoint, often sparsely to moderately pubescent with short, ascending hairs toward the tip; leaf blades flat or only shallowly concave, not folded longitudinally, the upper surface sparsely to moderately pubescent with minute, broad-based hairs, usually not or only slightly roughened to the touch ... 5. H. GROSSESERRATUS

Helianthus grosseserratus
13 7. Stems moderately roughened-pubescent with short, ascending hairs throughout, more densely so toward the tip; leaf blades folded longitudinally along the midvein at maturity, the upper surface moderately to densely pubescent with short, pustular-based hairs, strongly roughened to the touch ... 7. H. MAXIMILIANII

Helianthus maximiliani
14 1. Leaves all or mostly opposite (sometimes appearing all or mostly basal in H. occidentalis)

15 8. Disc florets with the corollas reddish brown to dark purple (at least the lobes and the upper portion of the tube); involucral bracts in 3 or 4 noticeably unequal, overlapping series, tightly appressed at flowering

16 9. Leaf blades lanceolate to narrowly ovate, (2.0–)2.5–8.0 times as long as wide, tapered to a sessile base or to a short, mostly winged petiole, tapered gradually to a sharply pointed tip or angled more abruptly to a sharply or bluntly pointed tip ... 11. H. PAUCIFLORUS

Helianthus pauciflorus
17 9. Leaf blades ovate to broadly ovate or nearly circular, 1.0–1.7(–2.0) times as long as wide, rounded or abruptly short-tapered to an unwinged, short petiole, rounded or broadly angled to a bluntly pointed tip ... 14. H. SILPHIOIDES

Helianthus silphioides
18 8. Disc florets with the corollas yellow; involucral bracts in 2–4 subequal, more or less overlapping series, loosely appressed and sometimes with spreading tips at flowering (except in H. occidentalis, with often unequal, sometimes more or less appressed bracts)

19 10. Leaves mostly basal, the 3–8 pairs of stem leaves much smaller than those of the basal rosette (occasionally the lowermost pair of stem leaves nearly as large as the basal ones); involucral bracts in 3 or 4 noticeably unequal, overlapping series, usually appressed at flowering ... 10. H. OCCIDENTALIS

Helianthus occidentalis
20 10. Leaves well distributed along the stems, gradually reduced toward the stem tip, the stem leaves usually 8–15 pairs (except rarely in depauperate plants); involucral bracts in 2–4 subequal, more or less overlapping series, the tips usually at least somewhat spreading at flowering

21 11. Heads relatively small, the involucre 5–7 mm long, 4–10 mm in diameter; ray florets 5–8, the corolla 1.0–1.5 cm long ... 8. H. MICROCEPHALUS

Helianthus microcephalus
22 11. Heads relatively large, the involucre 5–12 mm long, 15–30 mm in diameter; ray florets (8–)10–30, the corolla (1.5–)2.0–4.0 cm long

23 12. Stem leaves all sessile or with a minute petiole less than 5 mm long, the blade rounded or shallowly cordate at the base

24 13. Stems (at least above the midpoint) and leaves moderately to more commonly densely pubescent with short, spreading hairs and usually also shorter, ascending hairs, these mostly not pustular-based, usually appearing uniformly grayish, slightly to moderately roughened to the touch ... 9. H. MOLLIS

Helianthus mollis
25 13. Stems sparsely to moderately pubescent (at least above the midpoint) with short, stiff, loosely ascending to spreading, pustular-based hairs; leaves moderately pubescent, the upper surface with short, stiff, loosely ascending to spreading, pustular-based hairs, not appearing uniformly grayish, strongly roughened to the touch (the undersurface somewhat lighter in color and sometimes with somewhat softer hairs than the upper surface) (species sometimes difficult to distinguish)

26 14. Stems glabrous or hairy only toward the tip and along the inflorescence branches, sometimes somewhat glaucous; involucre 10–15 mm in diameter; disc florets with the corollas 4.0–5.5 mm long ... 4. H. DIVARICATUS

Helianthus divaricatus
27 14. Stems hairy throughout or at least above the midpoint, not glaucous; involucre (10–)15–20 mm in diameter; disc florets with the corollas (5.0–)5.5–6.5 mm long ... 6. H. HIRSUTUS

Helianthus hirsutus
28 12. At least the largest stem leaves short- to long-petiolate, the petiole more than 5 mm long or, if appearing nearly sessile, then the blade angled or tapered at the base to a poorly defined, winged petiole

15 Leaf blades with a single midvein; stems often with 20–25 pairs of leaves ... 5. H. GROSSESERRATUS

Helianthus grosseserratus
29 15. Leaf blades with 3 main veins, the lateral pair arching upward from at or near the blade base; stems usually with 8–20 pairs of leaves (species sometimes difficult to distinguish)

30 16. Stems glabrous or hairy only toward the tip and along the inflorescence branches, sometimes somewhat glaucous

31 17. Leaf blades relatively thin-textured, those of at least the larger leaves with the margins usually coarsely toothed; uppermost stem leaves usually alternate; petioles of at least the larger leaves 2–5 cm long; involucral bracts extending conspicuously beyond the disc florets (sometimes difficult to observe in pressed specimens) ... 3. H. DECAPETALUS

Helianthus decapetalus
32 17. Leaf blades relatively thick-textured, the margins entire or finely toothed; uppermost stem leaves usually opposite; petioles of the larger leaves 1–3 cm long; involucral bracts extending to about the tips of the disc florets ... 15. H. STRUMOSUS

Helianthus strumosus
33 16. Stems sparsely to moderately hairy, at least above the midpoint, not glaucous

34 18. Uppermost stem leaves usually opposite; largest leaves with the blade 0.7–9.0 cm wide, usually rounded or less commonly abruptly short-tapered to a relatively well-differentiated petiole 0.5–1.5 cm long; rhizomes not producing tubers ... 6. H. HIRSUTUS

Helianthus hirsutus
35 18. Uppermost stem leaves usually alternate; largest leaves with the blade 6–15 cm wide, tapered at the base to a partially winged, sometimes poorly differentiated petiole (1.5–)2.0–8.0 cm long; rhizome branches usually with small tubers at the tip ... 16. H. TUBEROSUS Helianthus tuberosus
 
 
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