Western Sunflower
Helianthus occidentalis
Aster family (Asteraceae)

Description: This perennial wildflower consists of a rosette of basal leaves up to 1' across, from which a flowering stalk develops that is 2-4' tall. The blades of the basal leaves are 2-7" long and 1-3" across; they are oval to ovate in shape and their margins are smooth (entire) or serrulate with sparse small teeth. The blades of basal leaves usually have rounded bottom and blunt tips. Their upper blade surfaces are medium green and rough-textured, while their lower surfaces are light green. In addition to their central veins, the basal leaves have 1-2 pairs of lateral veins that originate from the bases of their blades. The slender petioles of the basal leaves are 1-4" long and light green. The flowering stalk is light green to greenish red and glabrous to hairy; it is mostly naked, except for 1-2 pairs of opposite leaves below and a few alternate leaves above. The blades of opposite or alternate leaves are 1-3" long and -" across; they are lanceolate or elliptic in shape and usually smooth (entire) along their margins. The blades surfaces of these leaves are similar to those of the basal leaves, while their petioles are either absent or up to " long.



The flowering stalk terminates in 1-12 flowerheads that are usually arranged in a panicle. The peduncles of these flowerheads are -6" long. Individual flowerheads are 1-2" across, consisting of 8-22 ray florets that surround numerous disk florets. The petaloid rays are yellow and oblong to elliptic in shape. The tiny disk florets have tubular corollas that are yellow and 5-lobed. Around the base of each flowerhead, there are several overlapping phyllaries (floral bracts). These phyllaries are 5-7 mm. long, light green, linear-lanceolate in shape, and ciliate along their margins. The blooming period occurs from mid-summer to early fall, lasting about 1 month for a colony of plants. Afterwards, the fertile disk florets are replaced by achenes about 3-4 mm. in length. These achenes are broadly oblongoid and somewhat flattened in shape; they have a pair of scale-like awns that are early-deciduous. The root system consists of a narrow taproot with shallow rhizomes. Vegetative colonies of plants are sometimes produced from these rhizomes.

Cultivation: The preference is full sun, mesic to dry conditions, and sandy soil. This wildflower will also adapt to partial sun and rocky soil. On deep fertile soil, it is not competitive with other species of plants. This is one of the less aggressive Helianthus spp. (sunflowers).

Range & Habitat: The native Western Sunflower is occasional in the northern half of Illinois, while in the southern section of the state it is uncommon or absent. Habitats include upland sand prairies, sandy hill prairies, upland sandy savannas, limestone and sandstone glades, sandy areas along railroads, and sandy abandoned fields. This sunflower is usually found in higher quality habitats where the original ground flora is still intact.

Faunal Associations: The pollinators of Western Sunflower are probably similar to those of other sunflowers that grow in relatively open areas. This includes such insects and long-tongued bees, short-tongued bees, miscellaneous flies, and occasional butterflies. The following bees are oligoleges (specialist pollinators) of sunflowers (Helianthus spp.): Dufourea marginata, Andrena accepta, Andrena helianthi, Andrena aliciae, Melissodes agilis, and Pseudopanurgus rugosus. Other insects feed on the foliage, bore through the stems, feed on the florets and seeds, or suck plant juices from sunflowers. These species include: the leafhoppers Mesamia straminea and Mesamia nigridorsum; the aphids Uroleucon illini and Uroleucon rudbeckiae; the plant bugs Ilnacora stalii and Plagiognathus nigronitens; Haplorhynchities aeneus (Sunflower Head-Clipping Weevil) and Cylindrocopturus adspersus (Sunflower Stem Weevil); the leaf beetles Physonota helianthi and Trirhabda adela; Contarinia schulzi (Sunflower Midge) and Neotephritis finalis (Sunflower Seed Maggot); Melanoplus packardii (Packard's Grasshopper) and Sparagemon collare (Mottled Sand Grasshopper); and the flower thrips Heterothrips auranticornis (see Insect Table for a more complete listing of these species). In addition to these insects, the caterpillars of such butterflies as Chlosyne gorgone (Gorgone Checkerspot), Chlosyne nycteis (Silvery Checkerspot), and Vanessa cardui (Painted Lady) feed on sunflowers, as do the caterpillars of many moths (see Moth Table).



The seeds of wild sunflowers are a nutritious source of food for many birds, including the Mourning Dove, Eastern Goldfinch, White-Winged Crossbill, Bobwhite Quail, and several species of sparrows (see Bird Table). The seeds are also eaten by the Thirteen-Lined Ground Squirrel, mice, and voles. White-Tailed Deer and other hoofed mammalian herbivores browse on the flowering stalks and leaves of sunflowers. Because the Plains Pocket Gopher prefers many of the same habitats as the Western Sunflower in Illinois (open sandy habitats that are well-drained), it likely feeds on the roots, foliage, and seeds of this sunflower in some areas of the state.

Photographic Location: A flower garden in Urbana, Illinois. Because of a hot dry summer, the foliage of the photographed plant was unusually yellow.



Comments:
Because of its prominent basal leaves and nearly naked flowering stalks, the Western Sunflower has a very distinct appearance among Helianthus spp. (sunflowers). It resembles a petite Silphium terebinthinaceum (Prairie Dock), however the seeds of this latter wildflower are produced by the ray florets, rather than the disk florets. Also, the basal leaves of this latter wildflower are more toothed along their margins, more erect, and much larger in size. In spite of its distinct appearance, the Western Sunflower can form both natural and artificial hybrids with several species of sunflowers. One of these hybrids, Helianthus cinereus, has Helianthus mollis (Downy Sunflower) as the other parent. The common name of this species, Western Sunflower, is somewhat misleading, because it isn't native to the western United States. Instead, its distribution is centered in the upper Midwest.

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