Ageratina altissima (White Snakeroot)

Native to eastern North America, this herbaceous perennial forms upright clumps about 2 to 5 feet tall in woodland habitats. Flat-topped clusters of small white flowerheads appear from late summer into fall. Each head contains tubular disk flowers without the outer ray petals seen in many daisies. The small fruits have tufts of white hairs that aid wind dispersal. The plant is highly poisonous; milk from cows that have eaten it can cause milk sickness. Photographed in Florida.