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Wisconsin Plant of the Week

Helianthus giganteus L.

Asteraceae (Sunflower Family)

Common Name:

tall sunflower


Tall sunflower is a native perennial of moist, usually calcareous soil, in prairies, fens and openings in tamarack swamps. Like most of the sunflowers, characters of any individual plant can vary, but itís usually easily identified by its size -- up to 4 m tall -- and mostly alternate leaves on a rough, dark red or purple stem. Many other sunflowers have opposite leaves.

The flower heads are up to 7 cm across and bloom from July until mid-October. The leaves are lance shaped, shallowly toothed with a stalk or petiole less than 15 mm long.  Roots are short and thickened with no long rhizomes, so the plants grow quickly but usually in clumps rather than in large patches.

Only sawtooth sunflower (H. grosseserratus, FACW-, C = 2), another giant, is similar and more common. Sawtooth sunflower is distinguished by its smooth, often waxy, red stem,  sharply toothed leaves and longer petioles.

For more tips on identifying Helianthus, check out Helianthus strumosus in the Archive.

Wild Helianthus are an important source of genetic diversity to maintain production of cultivated sunflower (H. annuus). Like most crop plants it has rather narrow genetic variability. H. giganteus has been a particularly good source of traits for resistance and tolerance to damage by fungus, to predation by sunflower moth, and to variable moisture conditions, all of which severely limit crop production.

  • Origin of the name: Helianthus: helio, Gr., sun; antho-, Gr., flower; giganteus: gigas, Gr., a man of great size and strength.
  • Range:  N.B. to GA, w. to MN, MS
  • WI Range:  Statewide
  • Common associates: New England Aster, Joe-Pye Weed
  • Wetland Indicator Status: FACW
  • Coefficient of Conservatism: C = 9 (S&W), C = 5 (MI)
  • Reference:  H.-J. Henn, R. Wingender, H. Schnabl. (1998). Regeneration of fertile interspecific hybrids from protoplast fusions between Helianthus annuus and wild Helianthus species. Plant Cell Reports 18: p. 220-224.
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