Vascular Plants of North Carolina
Account for Giant Sunflower - Helianthus giganteus   L.
Members of Asteraceae:
Members of Helianthus with account distribution info or public map:
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Section 6 » Order Asterales » Family Asteraceae
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AuthorL.
DistributionLow Mountains, Piedmont, and the northwestern Coastal Plain. Not found (yet) south of Bertie and Halifax counties in the Coastal Plain.

N.B. to MN, south to northern GA, TN, and IL.
AbundanceFairly common in the northwestern Coastal Plain and northeastern Piedmont; infrequent over the rest of the Piedmont and mountains.
HabitatMoist to wet soil of damp meadows, forest borders, seepage slopes, roadsides ditches, and moist thickets. Strongly favors full sun and damp conditions, though is not a marsh species.
PhenologyFlowering and fruiting late July-October.
IdentificationTrue to its name, Giant Sunflower grows 3-9 feet tall, with a coarsely hairy stem, lance-shaped leaves that reach 7 inches long and are rough on the upper surface and that have very short stalks. The leaves are mostly alternate on the stem, a good field character, as most other sunflowers have opposite leaves. The disks and rays are yellow, but in this species the rays are often light yellow to canary yellow, a character from a long distance that can quickly identify this most striking species when in bloom. H. schweinitzii is also tall (to 9 feet) but differs in its green stems (vs. reddish), opposite leaves, revolute-margined leaves (vs. not curled under), and typically goldenrod yellow ray color (versus medium yellow to pale yellow).
Taxonomic CommentsNone

Other Common Name(s)Tall Sunflower
State RankS4
Global RankG5
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