Hydrocotyle

Hydrocotyle, sometimes called water pennywort, Indian pennywort, dollar weed, marsh penny, thick-leaved pennywort and even white rot 
is a genus of prostrate, perennial aquatic or semi-aquatic plants formerly classified in the family Apiaceae, now in the family Araliaceae.
Description.
Water pennyworts, "Hydrocotyles", are very common. They have long creeping stems that often form dense mats, often in and near ponds, lakes, rivers, marshes and some species in coastal areas by the sea. 
Selected species.
The genus "Hydrocotyle" has between 75 and 100 species. that grow in tropical and temperate regions worldwide A few species have entered the world of cultivated ornamental aquatics. A list of selected species:
Distribution.
"Hydrocotyleae" grow in wet and damp places in the tropics and the temperate zones.
Fossil record.
One fossil fruit of a "Hydrocotyle" sp. has been extracted from borehole samples of the Middle Miocene fresh water deposits in Nowy Sacz Basin, West Carpathians, Poland.