Alien Hydrocotyle species in Belgium
In Belgium, there is one native species of Hydrocotyle (Araliaceae): H. vulgaris, and three alien species, H. ranunculoides, H. sibthorpioides and H. verticillata.
Hydrocotyle ranunculoides was first recorded in Belgium in 1992 north of Gent. It is now a widespread invasive species and is common in Flanders though it also occurs in Wallonia. The species can cover slow moving water bodies and outcompetes vulnerable native aquatic vegetation and hinders human use of water bodies (for instance fishing or recreation).
Hydrocotyle sibthorpioides is believed to have been introduced into Belgium as a contaminant of bonsai plants from China. It is present in the Antwerp zoo since the 1980s where it grows on lawns and between pavement slabs. The species was originally identified as H. novae-zelandiae.
Hydrocotyle verticillata is morphologically very similar and often confused with the native, H. vulgaris. A well-established population of H. verticillata occurs in a recently created pond in the nature reserve D’Heye in Bredene (province of West Flanders). Here, H. verticillata completely covers the surface of the pond. H. verticillata is sold in plant nurseries and is likely to be more widely present in Europe than previously thought due to the misidentification with the native species.
Sources
Verloove F, Heyneman G (2021) A note on some alien species of Hydrocotyle (Araliaceae) in Belgium. Dumortiera 117 26-29.