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Helianthus

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)

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