A multi-faceted approach to determine the origins of Myriophyllum spicatum L. in southern Africa

A multi-faceted approach to determine the origins of Myriophyllum spicatum L. in southern Africa 
Philip S.R. Weyl, Julie A. Coetzee
Zoology and Entomology Department, Rhodes University, Grahamstown

Controversy over the status of Myriophyllum spicatum L. in South Africa (i.e. whether it is native or exotic) needs to be resolved before any irreversible management strategies are put in place. In this study we used a multifaceted approach to determine the status of this plant including historical records of distribution in southern Africa, population matching using genetics, morphological studies and herbivore diversity. Historical records suggest anthropogenic point source introductions, possibly with the transport of ornamental fishes. The genetic analysis suggests the southern African populations are unique, and could possibly be native. There are three main morphological biotypes of plants in southern Africa which, despite growing conditions, will not revert to a uniform original type, suggesting separate introductions or evolutionary variations of a native population. The lack of herbivore diversity is in contrast to the native range where in Europe 44 species in 10 families have been recorded, which suggests a lack of evolutionary history in the southern African region.

The status of M. spicatum has not yet been resolved from this study as there is evidence for and against being introduced to southern Africa. The recommendations from this study are that a cost benefit analysis be done before any further control measures are implemented for M. spicatum in southern Africa.