In the southwestern United States, Brassica tournefortii (Gouan) is a highly invasive plant that threatens native annuals. We conducted 5 experiments to help define the environmental limits for B. tournefortii germination. We found that this species germinates at a wide range of temperatures (16°C to 32°C), under moderate salt concentrations (up to 3.20 dS · m⁻¹), in 24 hours of light or darkness, and after 10 weeks of submergence in water. These germination characteristics make B. tournefortii a potentially vigorous competitor of native annuals in the Mojave Desert. The fact that B. tournefortii can take advantage of and effectively reproduce in habitat altered by Tamarix spp. adds to management concerns for controlling this species. That B. tournefortii seeds remain viable after extended submergence, combined with our observation that B. tournefortii can float across large bodies of water with seed pods intact, indicates that this species is a highly successful invader and may be a threat to natural environments, including remote shoreline habitats. We can no longer assume that shoreline habitats experiencing little to no human contact will be safe from invasions initiated by humans.