Ranunculus inundatus

Ranunculus inundatus, or river buttercup, is an amphibic plant originating from south-eastern Australia. There it grows on wet mud or in the waters of ponds and rivers. Ranunculus (buttercup) species are found in many wetlands all over the world, however, R. inundatus is one of the few that grow submersed, too.
Ranunculus papulentus, another Australian buttercup species, and closely related to R. inundatus, is also said to be imported as aquarium plant. However, those plants named R. papulentus in trade do not differ at all from those hitherto identified as R. inundatus. Especially their emersed forms correspond much better to the descriptions and illustrations of R. inundatus than those of R. papulentus (e.g. Flora of New South Wales).