How many, and which, plants will invade natural areas?

Of established nonindigenous plant species in California, Florida, and Tennessee, 5.8%, 9.7%, and 13.4%, respectively, invade natural areas according to designations tabulated by state Exotic Pest Plant Councils. Only Florida accords strictly with the tens rule, though California and Tennessee fall within the range loosely viewed as obeying the rule. The species that invaded natural areas in each state were likely, if they invaded either of the other states at all, to have invaded natural areas there. There was a detectable but inconsistent tendency for species that invade natural areas to come from particular families. At the genus level in California and Florida, and the family level in California, there was also a tendency for natural area invaders to come from taxa that were not represented in the native flora. All three of the above patterns deserve further studies to determine management implications. Only the first (that natural area invaders of one state are likely to invade natural areas if they invade another state) seems firm enough from our data to suggest actions on the part of managers.