Ageratina altissima

This herbaceous perennial plant is about 1.5 to 3 feet tall, branching occasionally. The light green to tan stems are terete and hairless. 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-crenate along their margins; they are medium to dark green on their upper surfaces and light green on their lower surfaces. There are 3 prominent veins on the upper surface of each leaf, while the lower surface has an elevated network of veins. The upper stems terminate in compound corymbs or flat-headed panicles of flowerheads. The branches of this inflorescence are light green and glabrous. Each flowerhead is about across and contains 10-30 disk florets that have brilliant white corollas and styles. There are no ray florets. At the base of each flowerhead, there is a single series of linear floral bracts that are light green and non-overlapping. The blooming period occurs from late summer through the fall, lasting about 2 months for a colony of plants. This is one of the last wildflowers to bloom during the fall. The flowers are often fragrant. White snakeroot got this name because early settlers believed it to be valuable in treating snakebite, but in fact, it is highly toxic, sickening cattle as well as humans who drink milk or eat meat from cows that have eaten the plant.