Economic and ecological problems brought by the invasion of non-native species can be prevented in part by identifying patterns in the invasion process. We tested hypotheses that address variation in the spatial, taxonomic, and temporal distributions of non-native floras in the large and diverse geographic area defined as California. Analyses reveal that in time, 79% of all non-native species will occur in disturbed habitat; polyploidy is not correlated with geographic spread; the Poaceae and Brassicaceae are the most broadly represented families across elevations; introductions increase from all geographic regions from 1925 to 1969, but more recently from Asia, Australia, Africa, South Africa, and South America; and more than 50% of all alien taxa recorded prior to 1925 have become widespread. Some taxa without native representatives contain some of the worst invaders in the flora, thus we suggest that control efforts should be directed to recent arrivals without native representation. Our conclusions support the need to control the spread of non-natives early in the invasion process but also emphasize the need to control invasions from a floristic perspective, both locally and regionally.
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Vol. 54 • No. 2