Helianthus L. (Asteraceae)

Helianthus comprises twenty-six species in North Carolina, including nine introduced taxa (i.e., H. annuus, H. argophyllus, H. grosseserratus, H. laetiflorus, H. maximiliani, H. mollis, H. petiolaris, and H. tuberosus). Only Helianthus schweinitzii is federally listed (Fed E, S3 G3). Helianthus floridanus (S1 G3G4) is currently state listed as threatened. Helianthus laevigatus is listed as SC-V (S3 G4). Helianthus occidentalis var. dowellianus is state historic (SC-H, SX G5T5).

North Carolina species of Helianthus can be divided into (1) annuals or perennials, and (2) species with basally disposed leaves or those with well-developed cauline leaves. As the listed species are all perennials and exhibit cauline leaves, no key is provided for the annuals or those species with basally disposed leaves (see Weakley [2010] for complete keys to these groups). Note that the color of the disk flowers can be variable within species and some, such as H. angustifolius, H. floridanus, and H. simulans, will exhibit red, yellow, or mixed red-yellow disk flowers.

Federally listed taxon—
Helianthus schweinitzii (Fed E, State E | S3 G3)

Habitat. Thought to occur historically in prairie-like habitats or Quercus stellata-Q. marilandica savannas maintained by fire; now often associated with roadsides, powerline cuts, open woodlands

Range. Endemic to the Piedmont of the Carolinas.

Additional resources. NHP | Recovery plan

Key to Helianthus in North Carolina

Key adapted from Schilling (2006 [FNA]) and Weakley (2008). Photos by Krings, unless otherwise indicated. Line drawings from Britton & Brown (1913). Maps courtesy of USDA PLANTS and the North Carolina Natural Heritage Program.

1. Leaves basally disposed, basal leaves persistent at anthesis [H. atrorubens, H. heterophyllus, H. longifolius, H. occidentalis var. dowellianus]...see Schilling (2006) or Weakley (2010)

1’. Leaves cauline, stem leafy for its length, basal leaves often lacking at anthesis...2.

2. Plant annual, tap-rooted (rarely surving to second year) [H. annuus, H. argophyllus, H. debilis ssp. cucumerifolius, H. petiolaris, H. porteri]...see Schilling (2006) or Weakley (2010)

2’. Plant perennial, rhizomatous and/or producing tubers...3.

3. Plant rhizomatous, but also producing tubers...4.

4. Tubers narrow, fusiform; leaves subsessile, petioles < 1 cm long...H. schweinitzii*

4'. Tubers broad, potato-like; petioles = or > than 2 cm long...H. tuberosus

3'. Plant rhizomatous only, not producing tubers...5.

5. Stems below the capitulescence glabrous or nearly so, sometimes glaucous; phyllaries usually not gland-dotted...6.

6. Abaxial leaf surface glaucous, glabrate or glabrous, not gland-dotted...7.

7. Phyllaries 12–15, laminae 12–14 mm long...H. glaucophyllus

7'. Phyllaries 23–28, laminae 15–20 mm long...H. laevigatus

6'. Abaxial leaf surface not glaucous, pubescent, gland-dotted...8.

8. Rays few (usually 5 or 8); involucres 9 mm wide or less...H. microcephalus

8’. Rays typically 10 or more (in larger heads); involucres usually > 9 mm broad...9.

9. Leaves sessile, bases rounded to cordate, trinerved from the base...H. divaricatus

9’. Leaves sessile to petiolate, bases narrower, triplinerved...10.

10. Anther appendages yellow...H. grosseserratus

10’. Anther appendages dark or reddish-brown...11.

11. Phyllaries equal to or slightly exceeding disk, apices acute; leaves moderately serrate to entire, abaxial surface usually densely gland-dotted; petioles 1–3 cm long...H. strumosus

11’. Longer phyllaries usually exceeding disk by half their length or more, apices acuminate; larger leaves moderately to notably serrate, abaxial surface sparsely gland-dotted; petioles 2–5 cm long...H. decapetalus

5’. Stems pubescent throughout, not glaucous; phyllaries gland-dotted, except not so in H. hirsutus and H. giganteus...12.

12. Leaves sessile, cordate...H. mollis

12’. Leaves petiolate or sessile, but not cordate...13.

13. Phyllaries attenuate, squarrose to reflexed, abaxial surface densely gland-dotted (at least apically)...H. resinosus

13’. Phyllaries acute to attenuate, not reflexed (or if so [H. giganteus], then not gland-dotted], abaxial surface sometimes gland-dotted...14.

14. Leaves usually 1-nerved, conduplicate, margins entire; inflorescence in spiciform or racemiform arrays...H. maximiliani

14’. Leaves triplinerved, not conduplicate; inflorescence more or less in corymbiform arrays...15.

15. Phyllaries usually appressed, strongly unequal...H. x laetiflorus

15’. Phyllaries usually loose or spreading, more or less subequal...16.

16. Leaves truncate to broadly rounded at base, shortly but distinctly petiolate; abaxial ligule surface gland-dotted...H. hirsutus

16’. Leaves cuneate to attenuate, gradually narrowing to base, sessile to petiolate; abaxial ligule surface gland-dotted or not (H. giganteus)...17.

17. Abaxial ligule surface not gland-dotted; leaves not strongly revolute...H. giganteus

17’. Abaxial ligule surface usually gland-dotted; leaves usually revolute...18.

18. Phyllaries appressed, ovate to broadly oblong, apex obtuse to acute...H. floridanus

18’. Phyllaries spreading, lanceolate to narrowly oblong, apex acute to acuminate...19.

19. Plants short, < 1.5 m tall; rhizomes lacking or poorly developed; leaves typically < 1 cm wide...H. angustifolius

19’. Plants robust, > 1.5 m tall; rhizomes well developed; leaves typically > 1 cm wide...H. simulans