Species that are considered high risk have a well-documented history of invasiveness in at least one location globally, and a high or medium climate match to the contiguous United States.
The history of invasion of Crassula helmsii is high. C. helmsii has caused problems in Europe since being introduced. This species has supplanted native vegetation in a number of different cases (Dawson 1994, Dawson 1996). C. helmsii is a listed noxious weed in several U.S. states. Substantial resources have been invested to reduce its impact in some environments. Climate matching indicated the contiguous United States has a high climate match. The certainty of assessment is medium. The overall risk assessment category is high.
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High Risk
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