The invasion status of Myriophyllum spicatum L. in southern Africa
The submerged aquatic macrophyte Myriophyllum spicatum L. (Haloragaceae) has been recorded in southern Africa since 1829. It was first considered problematic in 2005 on the Vaal River, which has highlighted the need for an assessment of the invasion status and an appropriate management strategy to be identified. We used a unified invasion framework to categorise M. spicatum in southern Africa and define appropriate management strategies. Historical records and field surveys were used to assess the invasion status. Populations were considered established if collection records from a particular catchment or river system spanned at least 10 years and in some cases several localities. Of the 21 river systems where it has been recorded, it was evaluated as established in 13 and in the D1-E category of invasion. The disjunct populations suggest that it was point source introductions and thus the major barrier that prevents M. spicatum from proceeding along the invasion framework is its inability to naturally disperse the greater distances between catchments. Appropriate management strategies need to be catchment or river system based depending on the stage or state and category of invasion. Where M. spicatum is in the D1-E stage – established and potentially spreading, the appropriate management strategies include containment, and where possible, mitigation.