Technical Abstract: Invasive plants are considered to be a major threat to the earth’s biodiversity and cost U.S. agricultural and forest producers billions of dollars each year from decreased productivity and increased weed control costs. While considerable effort is being spent studying exotic plant pests, little consideration has been given as to how invasive plants might react to the increasing concentration of CO2 in the atmosphere. Tropical spiderwort is considered one the world’s worst weeds and is becoming more of a problem in agricultural settings of the southeastern U.S. Growth responses of tropical spiderwort were evaluated under ambient and elevated levels of CO2. Although plant height was unaffected by CO2, both leaf and flower number tended to increase (~23%) when exposed to elevated CO2. Aboveground plant parts exhibited significant increases in dry weight when exposed to high CO2; leaf, flower, stem, and total shoot dry weights were increased by 36%, 30%, 48%, and 44% respectively. Additionally, total plant dry weight was increased by 41% for plants grown under high CO2. Root dry weight, as well as root length, were unaffected by CO2 concentration. Tropical spiderwort allocated more biomass to stems and tended to allocate less to roots when plants were exposed to high CO2. The strong aboveground growth response of the invasive weed tropical spiderwort suggests that its competitive ability with native plants may be enhanced in a future high CO2 environment.