THE BEAUTIFUL WATER HYACINTH EICHHORNIA CRASSIPES AND THE ROLE OF BOTANIC GARDENS IN THE SPREAD OF AN AGGRESSIVE INVADER

Abstract

Eichhornia crassipes originates from South America. It is an aquatic floating plant in freshwater lakes and slow-moving streams. Its growth is favored by nutrient rich water. Its native range is the Amazon basin, but nowadays it is introduced and cultivated in most warm countries. It has been imported from South America to decorate ponds and occasionally escaped into local environments and has thus spread to more than 50 countries on five continents. Nowadays, water hyacinth is one of the worst weeds in the world. Some cite the species as the worst aquatic weed worldwide. The Invasive Species Specialist Group (ISSG) has nominated this species as among 100 of the "World's Worst" invaders. After having been described scientifically in 1823 from the South American tropics it reached a botanic garden in Java because of its attractive flowers. From there – thrown into a river – it spread rapidly over tropical Asia. By 1905 it could be found all over the continent. 1880 it reached Europe and few years later Africa and North America. In 1962 the Kongo near Kinshasa carried 150 t of Eichhornia per hour. In the present study, we analysed the genetic diversity of populations in their native range and in invasive populations worldwide. The results showed that there were several diverse independent introductions worldwide, confirming worldwide weed reports which postulate different sites and origins of introductions. Given the environmental and economical dangers related to the expansion of E. crassipes – among others they affect boat traffic, fisheries and energy generation by plugging water turbines, they reduce flow velocity, choke irrigation channels, cause hypoxic conditions in the water, provide breeding grounds for disease-carrying insects – the role of botanic gardens as initiators of invasions must be taken seriously. Obviously their role for education and conservation prevails by far, but the historical dangers linked to the expansion of highly aggressive species with high growth rates and no local enemies should not be underestimated.