Cardamine Lyrata

Cardamine lyrata is actually a marsh plant from Japan. But it is also a familiar aquarium plant which thrives under water with 20-50 cm long stems. A characteristic trailing growth form makes it highly decorative, and ‘aerial’ roots often form on the plant itself.
Plant it in groups, and make sure the water temperature does not exceed 28 degrees C (this makes the leaves much smaller and the plant more leggy). Also suitable in garden ponds in the summer. 

 
*Exact plant may vary from photo shown