Prairie Sun

          Description: This herbaceous perennial plant is 2-4' tall. It is either unbranched or sparingly branched toward the apex. The central stem is green or reddish brown; it has scattered short white hairs that are quite stiff, providing a sand-papery texture. The opposite leaves are up to 6" long and 2" across, becoming slightly smaller and more narrow as they ascend the stem. However, one or two of the uppermost leaves may alternate along the stem. These leaves are lanceolate or narrowly ovate, tapering gradually at the base. They have short thick petioles, smooth or slightly serrate margins, and a rather rough texture because of scattered short stiff hairs and fine bumps on the surface. In hot dry weather, the leaves often curl upward along the central vein.
Each composite flower is about 2½–3" across, occurring individually at the apex of the central stem and any upper lateral stems. It consists of 10-25 yellow ray florets surrounding numerous reddish brown or yellow disk florets (the latter is atypical). Sometimes the ray florets fold along their length and assume a star-like quality in response to hot dry weather. The floral bracts (phyllaries) surrounding the base of each composite flower are triangular in shape and appressed together in 2-3 overlapping series. There is little noticeable floral scent. The blooming period occurs from late summer to fall, lasting 1-2 months. The root system produces numerous rhizomes, which enables this plant to form dense colonies quickly. These colonies of Prairie Sunflower tend to exclude other plant species because the roots exude allelopathic chemicals that inhibit seed germination and growth of young plants. Because Prairie Sunflower is somewhat vulnerable to these chemicals itself, the plants in the middle of a colony sometimes die out, creating a "fairy ring" effect.
Cultivation: The preference is full sun and mesic to dry conditions. The soil can contain significant amounts of loam, clay loam, sand, or gravelly material. This plant is easy to grow, but can spread and become very aggressive. Patches of powdery mildew may occur on the leaves. It is sometimes shy to flower.

Range & Habitat: The native Prairie Sunflower occurs occasionally in central and northern Illinois, but is uncommon or absent in many areas of southern Illinois (see Distribution Map). It is locally common in some prairie remnants, particularly along railroads. Habitats include mesic to dry black soil prairies, gravel prairies, sand prairies, hill prairies, limestone glades, and areas along railroads.