Ecological Risk Screening Summary - Tape Grass (Vallisneria spiralis) - Uncertain Risk

Species that are considered uncertain risk need a more in-depth assessment beyond the Risk Summary to better define the species’ risk to U.S. environments.

The history of invasiveness is uncertain. There are records of introductions attributed to Vallisneria spiralis around the world but recent molecular and taxonomic work has thrown uncertainty on the identifications of these populations outside of a European and Mediterranean range. There are records of generalized negative impacts, mostly replacement of native species as well as records of no impact and of beneficial impacts. Currently there is no way to determine if that range of impacts is the result of one species or different species in different locations. The climate match is high for both scenarios; however, the scenario using the more restricted range has a lower climate 6 score than the one using all potential populations as source points. The areas of highest climate match within the country change between the scenarios. The certainty of assessment is low due to the uncertainty in taxonomic classification and identification of populations. The uncertain history of invasiveness and low certainty in the assessment preclude a definitive risk assessment, combined with a high climate match it results in an overall risk assessment category of uncertain.