Woodland Sunflower
Helianthus divaricatus
Aster family (Asteraceae)

Description: This perennial wildflower is 2-6' tall with a central stem that becomes branched where the flowerheads occur. This stem is light green to dark purple, slender, terete (round in cross-section), glabrous to sparsely covered with short stiff hairs, and sometimes glaucous. Upper secondary stems have similar characteristics. Pairs of widely spreading opposite leaves occur along the central stem and any secondary stems; each pair of leaves rotates 90 from the pair of leaves below. Leaf blades are 2-6" long and -2" across; they are lanceolate-oblong to ovate-oblong in shape, and either toothless or with widely spaced teeth along their short-ciliate margins. The base of each leaf blade is rounded-truncate, while its tip is long and gradually tapering. The upper surface of the leaf blades is yellowish green to medium green and sparsely to moderately covered with short stiff hairs, while the pale lower surface is short-pubescent, especially along the major veins. Three prominent veins join together at the base of each leaf blade. The leaves are sessile or they have short ascending petioles (up to 1/8" or 3 mm. long).

The central and secondary stems terminate in flowerheads on slender peduncles. Individual flowerheads are 1-3" across, consisting of 8-15 ray florets that surround numerous disk florets. The yellow corollas of the ray florets are petal-like and widely spreading.. The yellow corollas of the disk florets are narrowly tubular (less than 1/8" or 3 mm. long) with 5 spreading lobes. At the base of each flowerhead, there are light green phyllaries (floral bracts) that are arranged in several overlapping series. Individual phyllaries are linear-lanceolate and ciliate along their margins; the outer phyllaries are widely spreading or recurved when the flowerheads bloom. The peduncles of the flowerheads resemble the stems, except they are more likely to have short stiff hairs. The blooming period occurs from mid-summer to early fall for about 2 months. Afterwards, the disk florets are replaced by achenes about 2 mm. long; these achenes are ovoid-oblongoid and somewhat flattened. At the apex of each achene, there is a pair of tiny chaffy scales that easily become detached. The root system is long-rhizomatous. Vegetative colonies of plants are often formed by the rhizomes.

Cultivation: The preference is full or partial sun, moist to dry-mesic conditions, and soil that is loamy, sandy, or rocky. This wildflower is easy to cultivate, although it may spread aggressively.

Range & Habitat: The native Woodland Sunflower is common in NE and SE Illinois, while in the rest of the state it is occasional. Habitats include upland rocky woodlands, sandy woodlands, thinly wooded bluffs, upland savannas and sandy savannas, woodland borders, sandy and non-sandy thickets, limestone glades, hill prairies, and moist to dry-mesic sand prairies. While this sunflower is normally found in relatively dry upland habitats, sometimes it also occurs in moist sandy habitats. Occasional wildfires tend to increase populations of Woodland Sunflower as this reduces competition from woody vegetation.

Faunal Associations: The nectar and pollen of the flowers attract a wide variety of insects. The following bees are specialist pollinators (oligoleges) of Woodland Sunflower and other sunflowers: Andrena accepta, Andrena aliciae, Andrena helianthi, Dufourea marginatus, Melissodes agilis, and Pseudopanurgus rugosus. Other floral visitors include long-tongued bees (honeybees, bumblebees, digger bees, leaf-cutting bees, cuckoo bees, etc.), short-tongued bees (Halictid bees and Andrenid bees), miscellaneous wasps, miscellaneous flies (Syrphid flies, bee flies, thick-headed flies, etc.), butterflies and skippers, and Chauliognathus pennsylvanicus (Goldenrod Soldier Beetle). Other insects feed on the foliage, bore through the stems, suck plant juices, etc., from sunflowers. These species include caterpillars of the butterflies Chlosyne nycteis (Silvery Checkerspot), Chlosyne gorgone (Gorgon Checkerspot), and Vanessa cardui (Painted Lady); the caterpillars of Cochylis hospes (Banded Sunflower Moth), Papaipema necopina (Sunflower Borer Moth), Stiria rugifrons (Sunflower Seed Copper), and other moths also feed on these wildflowers (see Moth Table). Sunflowers are important host plants for many aphids, treehoppers, leafhoppers, plant bugs, leaf beetles, scarab beetles, the larvae of weevils, the larvae of midges and other small flies, grasshoppers, and other insects (see Insect Table). Some vertebrate animals use sunflowers as a food source. The seeds of these wildflowers are eaten by the Hungarian Partridge, Bobwhite, Mourning Dove, Eastern Goldfinch, Tufted Titmouse, Harris Sparrow, and many other birds. Small mammals that occasionally eat the seeds include the Gray Squirrel and other tree squirrels, Thirteen-Lined Ground Squirrel, Meadow Vole, White-Footed Mouse, and Plains Pocket Gopher. This gopher also feeds on the rhizomes of sunflowers in relatively dry sandy areas. The Cottontail Rabbit browses on the foliage of seedlings and lower leaves of mature plants, while the White-Tailed Deer occasionally chomps off the stems and upper leaves of mature plants. Because the Woodland Sunflower and other sunflowers are relatively tall and often form dense colonies, they provide good ground cover for many kinds of wildlife.

Photographic Location:
A moist sand prairie at the Indiana Dunes National Lakeshore in NW Indiana.

Comments: The Woodland Sunflower is easily identified by its sessile, or nearly sessile, opposite leaves. Other sunflowers (Helianthus spp.) have longer petioles. Its stems are usually hairless or mostly hairless, unlike Helianthus hirsutus (Hairy Sunflower) and some other species in this genus. Compared to some narrow-leaved sunflowers that occur in prairies, the leaf bases of Woodland Sunflower are more broad and nearly truncate. Some parasitic plants that occasionally attach their haustoria (root-like extensions) to sunflowers and other species in the Aster family include Cuscuta glomerata (Rope Dodder) and other Cuscuta spp. (generally in moist areas that are often sandy), and Orobanche ludoviciana (Prairie Broomrape) and other Orobanche spp. (generally in dry areas that are often sandy). These parasitic plants can significantly weaken the host plants to which they become attached.