Annual Sunflower

Annual Sunflower, Common Sunflower

Helianthus annuus L.

Asteraceae (Aster Family)

▲ ▼ young plants

▲ ▼ mature flowering plants

▲ ▼ flowers

▲ bracts at base of flower

▲ rough hairs on stems

▲ common sunflower along highway in western Kansas

Helianthus annuus L., Annual Sunflower: (Bayer Code: HELAN; US Code HEAN3)

U.S. native summer annual that grows 3-10 feet tall with ridged, green stems that often branch at the nodes, particularly in full sun; both leaves and stems are rough-hairy
Leaves are opposite, heart-shaped to triangular, large, with 3 main veins emerging at base where petiole joins the leaf and toothed margins; petiole is long--often equal to, or slightly less than, length of leaf
Head inflorescences are 3-6 inches in diameter, the typical sunflower shape, but usually smaller than the cultivated species
Each head has 15-30 bright yellow disk florets (“petals") that are have round-pointed tips, and are often kind of puckered where they join the head
There are from 100 to 1000 disk florets that are orange to brown
Bracts below the inflorescence are in several rows, large, oval-triangular or lanceolate, with an extended pointed tip; bracts are rough-hairy and stand out from the base of the head; edges of bracts have stiff hairs
Flowering from summer through autumn
Native annual sunflowers are usually have more branching and more, but smaller flowers than cultivated sunflowers
Allelopathic to itself (autotoxic) and other plants for several years after initial planting
Spreads rapidly by seed in cultivated fields, prairies, pastures, waste areas
Not often in strong competition with crops, but its allelopathic nature may make it undesirable in fallow field, where it can be a strong presence
A similar-appearing, more western relative, Prairie Sunflower (Helianthus petiolaris) has slightly smaller, more elongated-triangular to lanceolate leaves that are less hairy and somewhat glossy, with longer petioles, and much longer peduncles (stalks) below the inflorescences

(Updated January 21, 2021)

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