Description: This native perennial plant is about 1½–3' 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 ½–2½" 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.