Hydrocotyle sp."Japan" is the popular name of the plant in different plant forums. It is a variant of Hydrocotyle tripartita ( Dwarf Pennywort ) from South-East Asia. It is characterized by fast, compact growth and small, intense green leaves on vertical stems. The plant is carpet-forming (5-10 cm tall), and its dense growth can be promoted by physically pressing the carpet with your hand when maintaining your aquarium. Carpet formation and compact growth do best in strong light.
Light Needs: Moderate
Plant Structure: Stem
Location: Southeastern Asia
Growth Rate: Medium
Potted plants are started in rock wool. To plant, remove as much rock wool as possible. Most of the rock wool will pull off. If you have any left and want it off, shake the plants gently by holding it by the roots and shaking in water. Leaving some rock wool will help anchor the plant in your substrate.
Separate the plant into 1/8" pieces with roots and plant 1/8" to 1/4" apart in your substrate. This will leave room for the plant to propagate and spread. If you want instant gratification, you can plant closer. It will take more plants to fill in the area you want to cover when planting closer.
Only plant the root in your substrate, not any of the plant itself or this can cause melting or shock, for more information on planting and caring for your plants, please go here