Hydrocotyle ranunculoides L.f. – Origins and Control Options.

Abstract

Hydrocotyle ranunculoides L.f. is an invasive aquatic macrophyte. The origin is considered by some to be North America, but the presence of co-evolved insect herbivores suggests a South American origin with spread through Central America to North America at some time in the recent past. Outside its’ native range it is widespread in the United Kingdom, the Netherlands, Belgium, and present in France, Ireland, Italy, Germany, Australia, Angola, Ethiopia, Kenya, Malawi, Tanzania, Uganda, Democratic Republic of Congo, Madagascar, Rwanda, Zimbabwe and possibly also Sudan. Wherever it grows in introduced areas it is considered to be a problematic invasive species, and although it can be dominant in some South American wetland sites, the scale of the habitat reduces the impact of the species in such situations. There is some evidence to suggest that warm tropical wetland sites encourage heterotrophic nutrition at the expense of photosynthetic C3 metabolism, and the evolution of aggressive floating macrophytes is a response to lack of carbon in the aquatic environment. H. ranunculoides is an example of such a species. Data from work on nutrient conversion in aquatic habitats in the UK will be presented. Control options for the species are limited, with mechanical control being the most popular option, although chemical control can be successful with adjuvants. Biological control offers the greatest potential for sustainable management of this species in introduced habitats and preliminary data will be presented that indicate the high potential for biological control of H. ranunculoides in Europe