Aster family (Asteraceae)
Description: This native perennial plant is about 1½3' tall, branching occasionally. The light green to tan stems are round and largely hairless. The opposite leaves are up to 6" long and 3½" across, becoming smaller as they ascend the stems. The lower leaves are cordate to cordate-ovate, while the upper leaves are broadly lanceolate to lanceolate. All of the leaves are largely hairless and strongly serrated along the margins. There are 3 prominent veins on the upper surface of each leaf (particularly the lower ones), while the lower surface has an elevated network of veins. The rather long petioles are ½2½" in length.
The upper stems terminate in compound corymbs of flowerheads that span several inches across. Each flowerhead is about ½" across and contains 10-30 disk florets that are brilliant white. There are no ray florets. Each disk floret is about 1/5" across when fully open; it consists of a small tubular corolla with 5 lobes that are spreading and pointed, and it has a divided style that is strongly exerted from the corolla. At the base of each flowerhead, there is a single series of linear floral bracts that are green and non-overlapping. The blooming period occurs from late summer through the fall and lasts about 2 months. This is one of the last wildflowers to bloom during the fall. The flowers are often fragrant. Each disk floret is replaced by a dark linear achene with a small tuft of white hairs. These achenes are distributed by the wind. The root system consists of spreading rhizomes and shallow fibrous roots. This plant can spread vegetatively by means of its rhizome, or it can reseed itself into new areas.
Cultivation: The preference is partial sun to light shade, moist to slightly dry conditions, and a soil that is loamy, slightly rocky, or slightly gravelly. This plant dislikes too much sun, otherwise it is easy to grow.
Range & Habitat: White Snakeroot is a common plant that occurs in almost every county in Illinois (see Distribution Map); it is quite likely that this species occurs in every county. Habitats include moist to slightly dry deciduous woodlands, woodland borders, thickets, partially shaded to shady seeps, bluffs, woodland meadows along rivers, powerline clearances in woodlands, shady corners of pastures and yards, fence rows with woody vegetation, and overgrown vacant lots. This species is especially common in wooded areas that are rather disturbed and degraded, although it also occurs at higher quality sites.
Faunal Associations: The nectar of the flowers attracts a variety of insects, including large Leaf-Cutting bees, Halictid bees, wasps, various flies (Syrphid, Tachinid, Bee flies, & others), butterflies, and moths. The bees also collect pollen. The caterpillars of some moths are known to feed on Eupatorium spp. (Bonesets), including White Snakeroot (probably). These species include Carmenta bassiformis (Eupatorium Borer Moth), Papaipema cataphracta (Burdock Borer Moth), Phragmatobia fuliginosa (Ruby Tiger Moth), and Phragmatobia lineata (Lined Ruby Tiger Moth). Because the foliage is bitter and toxic, mammalian herbivores avoid this plant as a food source. Sometimes cattle will eat it in overgrazed pastures, which can produce fatal results.
Photographic Location: A powerline clearance at Busey Woods in Urbana, Illinois.
Comments: The common name of this species derives from the erroneous belief among early settlers that the bitter rhizomes were beneficial in the treatment of snakebites. In fact, the foliage and rhizomes are highly toxic, causing fatalities from 'Milk Sickness' because the toxins can pass through the milk of dairy cattle to humans. White Snakeroot has been reassigned recently to the genus Ageratina, although it is still often referred to as Eupatorium rugosum. Normally, White Snakeroot is largely hairless, although some authorities describe a pubescent variety of this species. White Snakeroot resembles many of the white-flowered Eupatorium spp. (Bonesets), but these different species can be distinguished from each other by the appearance of their leaves. Among the species in this group, White Snakeroot has the broadest leaves; its lower leaves are cordate or broadly ovate, and these leaves have long petioles. White Snakeroot usually occurs in and around shady woodlands, while many of these other species are found in prairies and sunny wetlands.