This perennial wildflower is 3-9' tall, forming a central stem that is unbranched, except along the upper one-third of its length, where there may be a few ascending lateral stems. These stems are predominately reddish purple and terete; they are covered with spreading white hairs. Abundant spreading leaves occur along these stems; they are usually opposite below and alternate above. Individual leaves are 3-7' long and ½-1½' across; they are lanceolate-elliptic in shape and usually crenate-serrate along their margins. The upper leaf surface is medium green and rough-textured from minute stiff hairs, while the lower surface is pale green with spreading white hairs along the major veins and minute stiff hairs inbetween. The minute stiff hairs of the leaves are sparsely to moderately abundant in their distribution. Individual leaves taper gradually into short petioles up to ½' long, and they taper gradually into acute tips. The upper stems terminate in one or more flowerheads about 2-3' across. Each flowerhead has 10-20 yellow ray florets that surround a dense circular cluster of yellow disk florets in the center. The petaloid extensions of the ray florets are oblong and slightly notched at their tips. The tiny disk florets are tubular in shape with 5 spreading to ascending lobes. The disk florets are perfect, while the ray florets are sterile. At the base of each flowerhead, there are floral bracts (phyllaries) that are loosely arranged in several series; they are ascending to widely spreading when the flowerhead is in bloom. Individual floral bracts are medium green, narrowly linear-lanceolate, and covered with stiff minute hairs; their margins are often ciliate. The peduncles (up to 6' long) of the flowerheads are similar to the stems, except they are usually light green. The blooming period occurs from mid-summer into the fall, lasting about 2 months. The disk florets are replaced by small achenes that are oblongoid and slightly flattened in shape; each achene has a truncate apex with a pair of membranous awns that soon become detached. The root system has fleshy fibrous roots and shallow rhizomes. Small colonies of plants often develop from the rhizomes.

The native Giant Sunflower is largely restricted to NE Illinois, where it is rare and state-listed as 'endangered.' It is more common in areas further to the north and east of Illinois. Habitats consist of wet sand prairies, sandy swales, calcareous fens, sedge meadows, and Tamarack bogs. This wildflower is found in higher quality wetlands.

Helianthus validus E. Watson:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Helianthus alienus E. Watson:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Helianthus giganteus L.:
Canada (North America)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Perennials, 100–400 cm (rhi-zomatous). Stems (usually reddish) erect, hairy. Leaves cauline; mostly alternate; petioles 0–1.2 cm (ciliate); blades (3-nerved from bases) lanceolate to lance-ovate, 7–20 × 1.2–3.5 cm, bases cuneate, margins serrulate to subentire (± flat), abaxial faces scabrous or ± hirsute, sometimes gland-dotted. Heads 1–12. Peduncles 8–12 mm. Involucres hemispheric, 10–24 mm diam. Phyllaries 20–25 (loose or spreading), linear, 8–15 × 1.2–2 mm, (margins usually ciliate) apices acute to attenuate , abaxial faces sparsely strigose, not gland-dotted. Paleae 7–9 mm, entire or ± 3-toothed (apices acute, hairy). Ray florets 12–20; laminae (often pale yellow) 15–25 mm (abaxial faces not gland-dotted). Disc florets 60+; corollas 5–6 mm, lobes yellow; anthers dark brown or black, appendages dark. Cypselae 3–4 mm, glabrate; pappi of 2 aristate scales 2.4–3 mm. 2n = 34.

Helianthus alienus E. Watson; H. validus E. Watson

The native Giant Sunflower is largely restricted to NE Illinois, where it is rare and state-listed as 'endangered.' It is more common in areas further to the north and east of Illinois. Habitats consist of wet sand prairies, sandy swales, calcareous fens, sedge meadows, and Tamarack bogs. This wildflower is found in higher quality wetlands.

The nectar and pollen of the flowerheads attract bumblebees and other long-tongued bees, Andrenid bees and other short-tongued bees, Syrphid flies and other flies, butterflies, and other insects. A variety of insects feed on the foliage, stalks, roots, and other parts of Giant Sunflower and other sunflowers (Helianthus spp.). These species include such beetles as Haplorhynchites aeneus (Sunflower Head-Clipping Weevil), Cylindrocopturus adspersus (Sunflower Stem Weevil), Rhodobaenus quinquepunctatus (Five-Spotted Billbug), Rhodobaenus tredecimpunctatus (Thirteen-Spotted Billbug), Systena blanda (Pale-Striped Flea Beetle) and other leaf beetles. The larvae of Contarinia schulzi (Sunflower Midge) cause club-shaped distortions in the buds and flowerheads, while the larvae of Strauzia longipennis (Sunflower Maggot) bore through the stems. The larvae of another fly, Neotephritis finalis (Sunflower Seed Maggot), feed from inside the achenes. Other insect feeders include the flower thrips Heterothrips auranticornis and the following plant bugs

Helianthus giganteus (Giant Sunflower)
(Bees collect pollen or suck nectar; flies feed on pollen or suck nectar; beetles feed on pollen only and are non-pollinating; other insects suck nectar; all observations are from Graenicher, except for those by Krombein et al. as indicated below)

Bees (long-tongued)
Apidae (Apinae): Apis mellifera sn cp; Apidae (Bombini): Bombus affinis sn cp, Bombus griseocallis sn, Bombus pensylvanica sn, Bombus vagans sn cp; Anthophoridae (Eucerini): Melissodes trinodis sn cp; Anthophoridae (Nomadini): Nomada graenicheri sn; Anthophoridae (Xylocopini): Xylocopa virginica sn; Megachilidae (Megachilini): Megachile latimanus sn

Bees (short-tongued)
Halictidae (Halictinae): Augochlorella striata sn; Andrenidae (Andreninae): Andrena accepta cp olg (Kr), Andrena aliciae sn cp olg (Gr, Kr), Andrena chromotricha sn cp, Andrena helianthi sn cp olg (Gr, Kr)

Wasps
Vespidae (Eumeninae): Euodynerus foraminatus

Flies
Bombyliidae: Sparnopolius confusus; Syrphidae: Eristalis tenax, Eristalis transversus; Calliphoridae: Lucilia illustris; Muscidae: Musca domestica

Butterflies
Pieridae: Colias philodice, Pieris rapae; Papilionidae: Papilio polyxenes asterias

Beetles
Chrysomelidae: Diabrotica undecimpunctata fp np

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 2
Species With Barcodes: 1

Rounded Global Status Rank: G5 - Secure

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: NNR - Unranked

The preference is full sun, wet to moist conditions, and sandy soil. The size of individual plants is highly variable, depending on the level of moisture, nutrients, and competition from other plants.

Helianthus giganteus was probably introduced in Newfoundland. It intergrades with H. nuttallii and H. grosseserratus; it is distinctive in its hairy, reddish-colored stems, dark anther appendages, and prominent setae on the petioles. The natural hybrid of H. giganteus with H. grosseserratus has been called H. luxurians E. Watson (R. W. Long 1954). Hybrids of H. giganteus with H. divaricatus have been referred to as H. ambiguus (Torrey & A. Gray) Britton and H. ×divariserratus R. W. Long (Long 1954).