The aims of this study were to evaluate the effects of light and temperature on seed germination and the effect of light on seedling emergence of Clausena excavata, an invasive exotic species. Seeds were incubated at constant temperatures (10 to 40 ºC), under continuous white light and darkness. Seedling emergence was evaluated under full sun and canopy shade. There was no significant difference between seeds germinated in the presence or absence of light at temperatures between 20 and 35 ºC. Seeds maintained at 20 ºC germinated more slowly than other temperatures. Independent of temperature, seed germination was much more synchronised under white light than under darkness. In the field, emergence occurred in both environments, but a greater percentage was observed under full sun. Seedling emergence occurred at the same rate and synchronisation index under both conditions. C. excavata has a high invader potential in open areas and shaded environments.