In controlled-environment chambers, serrated tussock achieved maximum growth in temperature regimes of 18/11, 18/23, 24/23, or 24/17 C day/night. Growth was significantly reduced at 30/11 C, and no plants survived at 36/29 C. Serrated tussock seedlings grew slowly at first but eventually produced vigorous tussocks with as many as 2800 tillers after 140 d in the 24/17 C regime. Comparisons of climatic conditions in New South Wales, Victoria, New Zealand, South Africa, and the United States revealed that similar temperature conditions occur during the warmest eight mo of the year in areas as diverse as Oregon, Washington, the Sierran Nevada foothills of California, upper elevation rangelands in Arizona, and the southern Appalachian highlands. None of these areas has a precipitation pattern similar to those of the sites of serrated tussock weed infestation in the Southern Hemisphere. However, poorly managed pastures and unimproved rangelands in these diverse areas may be vulnerable to invasion by serrated tussock, should the weed become established in the United States.