Weeds of Container Nurseries in the United States

American burnweed

American burnweed and thickhead are very similar before they flower. Young seedlings have elliptic leaves with finely toothed margins; midveins are often tinged red. As plants mature they grow upright with toothed leaves clasping the stem. American burnweed is a native with more elongated leaves and white flowers, and can reach 5 to 8 feet in height. Thickhead is a recently introduced species with red flowers, broader leaves and a shorter stature, generally less than 4 feet tall. Additionally, flower heads of American burnweed are held upright, whereas thickhead flowers droop downward as though the plants were experiencing moisture stress. Both species are summer annuals with seedlings emerging from spring through late summer. Plants flower in summer to early fall then die after frost. Seeds are wind dispersed and can produce multiple generations each growing season. These species can be controlled by preemergence broadleaf herbicides registered for nursery use. Escaped plants will occur and are readily visible due to their height.

thickhead