Kendall County (IL) Forest Preserve District
White Snakeroot
Ageratina altissima [C-value 4]
Aster family (Asteraceae)
Blooms
August -
October
The native White Snakeroot is common in our area. It prefers partial sun to light shade and moist to slightly dry loamy soil. Habitats include deciduous woodlands, woodland borders, thickets and partially shaded seeps. This perennial is 1½–4' tall, branching occasionally, with opposite leaves up to 5" long and 3½" across, becoming smaller as they ascend the stems. The leaves are hairless and strongly toothed with 3 prominent veins on the upper surface. The upper stems terminate in compound flat-headed panicles of flowers spanning 2-6" across. Each flower is about ½" across and contains 10-30 disk florets. Each disk floret is about 1/8" across with a small tubular brilliant white corolla with 5 lobes.
White Snakeroot at Richard Young Forest Preserve September 19, 2012
White Snakeroot foliage at Richard Young Forest Preserve August 13, 2013
White Snakeroot foliage at Richard Young Forest Preserve August 10, 2012
White Snakeroot often has these elaborate, curving "snake" trails on some leaves. They are the work of a species of fly (Liriomyza eupatoriella) that makes white snakeroot its host. The fly lays its eggs on the leaf, and after they hatch, the larvae feed on the leaf tissue, tunneling their way around and creating the beautiful patterns.
White Snakeroot (huge colony) at Richard Young Forest Preserve September 19, 2012
White Snakeroot (fall seed heads) at Richard Young Forest Preserve October 29, 2014
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 and caused fatalities from "Milk Sickness" because the toxins can pass through the milk of dairy cattle to humans. Abraham Lincoln's mother grew delirious and swiftly died with the "milk sickness". It wasn't until well into the nineteenth century before anyone finally deduced that the "bad milk" came from cows grazing on the pasture plant called White Snakeroot. The toxin tremetol in White Snakeroot remains active after the plant dies so farmers today have to make sure it is not growing in their hay fields as well as pastures.
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