Another common name for this plant is Common Ironweed. However, in southern Illinois, this species is not common. Smooth Ironweed is one of the smaller Ironweeds with a compact inflorescence and smooth hairless leaves. Other Ironweed species have hairy stems or leaves. An exception is Vernonia gigantea (Tall Ironweed), which has hairless leaves and stems upon occasion. However, Tall Ironweed has a spreading inflorescence, and it is usually a taller plant (as the name implies). The larger leaves of Tall Ironweed exceed ½" across, while the leaves of Smooth Ironweed are ½" or less. Some authorities state that Smooth Ironweed has black dots on the undersides of the leaves, but this is not always true. The species in this genus are occasionally difficult to identify because they can hybridize with each other.