Your help is appreciated.    We depend on donations to help keep this site free and up to date for you. Can you please help us?


See list of 15 species in this genus

Identification of Helianthus is complicated by phenotypic plasticity, polyploidy, and occasional hybridization. Micromorphological characters are a great asset within this genus and are used extensively in the key (e.g., anther appendage and style branch colors, disk corolla indument, cypsela size and indument). Reference: Schilling (2006).

  • 1a. Plants annual, with fibrous roots; leaves alternate (except the lowermost); receptacle flat or nearly so; disk corollas red-purple (sometimes yellow in H. annuus)
    • 2a. Involucral bracts narrow-oblong to ovate, (3–) 5–8 mm wide, abruptly narrowed to the apex, conspicuously long-ciliate; cypselas usually glabrous except near the pubescent apex, 4–8 mm wide; style branches yellow; leaf blades 5–25 cm wide, dentate; plants (0.5–) 1–3 m tall
    • 2b. Involucral bracts lanceolate, 1–4 (–5) mm wide, gradually narrowed to the apex, either eciliate or ciliate with short hairs of similar length to the hairs of the abaxial surface; cypselas pubescent, 1.2–2.5 mm wide; style branches red (rarely yellow in H. debilis); leaf blades 1.5–9 cm wide, entire to undulate-dentate; plants 0.4–1 (–1.5) m tall
      • 3a. Chaff near the center of the disk inconspicuously short-pubescent; cypselas mottled, pubescent with spreading-ascending hairs; stems frequently mottled; leaf blades dark green and scabrous
      • 3b. Chaff near the center of the disk conspicuously pubescent near the apex with long, white hairs; cypselas not mottled, pubescent with appressed-ascending hairs; stems not mottled; leaf blades pale green and strigose
  • 1b. Plants perennial, with rhizomes, stolons, tuberous roots, and/or tough, overwintering bases; leaves opposite (except often the upper); receptacle usually convex to some degree; disk corollas yellow (red-purple in H. pauciflorus)
    • 4a. Reproductive stems with 3–5 (–8) nodes bearing highly reduced leaves (rarely the lower 2–4 nodes with well-formed blades), often the upper 50% of the stem lacking leaves; plants with a basal rosette of leaves
    • 4b. Reproductive stems with (5–) 6–15 or more leaf-bearing nodes, the blades gradually, if at all, descreasing in size upward, only the upper 25% or less of the stem lacking leaves; plants without a basal rosette of leaves, during anthesis the leaves chiefly cauline (except sometimes in H. pauciflorus)

Show All Couplets

 Show photos of:   Each photo represents one species in this genus.