Hydrocotyle sp.'Japan' is the popular name of the plant in different plant forums. It is a variant of Hydrocotyle tripartita from South-East Asia. It is characterised by fast, compact growth and small, intense green leaves on vertical stems.
The plant is carpet-forming (5-10 cm tall) and its compact growth can be promoted by physically pressing the carpet with your hand when maintaining your aquarium (mechanical retardation). Carpet formation and compact growth do best in good light. 
 
Plant info
Type:
Stem
 
Origin:
Asia
 
Country or continent where a plant is the most common. Cultivars arise or are bred in cultivation.
Growth rate:
High
 
Growth rate of the plant compared to other aquatic plants.
Height:
5 - 5+
 
Average height (cm) of the plant after two months in the tank.
Light demand:
Medium
 
The average or medium light demand of an aquarium plant is 0,5 W/L.
CO2 :
Low
 
A medium need in CO2 is 6-14 mg/L. A high demand in CO2 is approx. 15-25 mg/L.