A note on some alien species of Hydrocotyle (Araliaceae) in Belgium

An adventive Hydrocotyle (Pennywort) that has been established in lawns in the Antwerp Zoo since the 1980s appears to belong to H. sibthorpioides, not to H. novae-zelandiae as originally assumed. A second Belgian locality was recently discovered in Knokke. A few years ago, a population of H. verticillata has furthermore been found in Bredene. This is an aggressive, subtropical lookalike of native H. vulgaris. Diagnostic features of both H. sibthorpioides and H. verticillata are briefly discussed and both are depicted. A key for the identification of the species currently found in Belgium is presented.