Flowerheads about ¾" across occur individually on erect peduncles about 1-5" long. Each flowerhead has 5-10 ray florets surrounding numerous tiny disk florets (75 or more); both types of florets are yellow. The petal-like rays become wider toward their tips, where they are 3-toothed; their florets are pistillate and fertile. The disk florets have tubular corollas with 5 tiny teeth along their upper rims; they are perfect and fertile. At the base of each flowerhead, there are several linear-lanceolate bracts (phyllaries) that are light green; they extend downward while the flowerhead is blooming. The blooming period occurs from late summer into the fall and lasts 1½-3 months. Both the disk and ray florets are replaced by small achenes (about 1-1.25 mm. in length) that are reddish brown, oblanceoloid, angular, and hairy. Each achene has a crown of several awned scales at its apex. The root system consists of a short branching taproot. This wildflower spreads into new areas by reseeding itself.
Cultivation: The preference is full sun, dry-mesic to dry conditions, and barren ground containing gravel or sand. The lower leaves often wither away before the flowerheads bloom.
Range & Habitat: The native Bitterweed is occasional in southern Illinois, while in the rest of the state it is rare or absent (see Distribution Map). Habitats consist of upland prairies, rocky glades, gravelly areas along railroads, roadsides, pastures, and open sandy ground. Bitterweed is somewhat weedy, preferring disturbed areas. It is more common in the southeastern states.
Faunal Associations: The nectar and pollen of the flowerheads attract a wide variety of insect visitors, including long-tongued bees, short-tongued bees, wasps, flies, butterflies, skippers, and beetles. The caterpillars of two moths, Papaipema impecuniosa (Aster Borer Moth) and Papaipema rigida (Rigid Sunflower Borer Moth), bore through the stems and roots of Helenium spp., while larvae of Smicronyx discoideus (Sneezeweed Weevil) feed on the florets and seeds. Two plant bugs, Lygus lineolaris (Tarnished Plant Bug) and Polymerus basalis (Red-spotted Aster Mirid), feed on Bitterweed. In prairies and other open areas, the Greater Prairie Chicken eats the seeds and/or dried seedheads. Because the foliage is bitter and toxic, it is usually avoided by mammalian herbivores. When dairy cows graze on the foliage of Bitterweed in overgrazed pastures, it provides their milk with a bitter taste. If the foliage is eaten in sufficient quantities, it can kill horses and other domesticated farm animals.
Photographic Location: A flower garden at the Arboretum of theUniversity of Illinois in Urbana, Illinois.
Comments: This is one of many wildflowers in the Aster family that produces showy yellow flowerheads during the summer and fall. Like other species in its genus, the flowerheads of Bitterweed have very distinctive petal-like rays with broad 3-toothed tips. Bitterweed is also distinguished by its very narrow leaves (less than 1/8" or 3 mm. across) that are nearly filiform; they often occur in short clusters along the stems. Other Helenium spp. in Illinois have wider leaves and they prefer habitats that are more damp.