Dwarf Pennywort aka Lawn Marshpennywort
Hydrocotyle sibthorpioides
syn: H. tripartita
formerly:  H. maritima

Hydrocotyle sibthorpioides is a small foreground species native to southeastern Asia.  It is an adaptable plant that can be found growing in a wide variety of conditions ranging from relative dryness to full submergence.  In the past this plant was only found for sale through European plant nurseries.  Although it remains rare in the United States, Arizona Aquatic Gardens has it for sale. 

H. sibthorpioides features a creeping growth habit.  Under good conditions and high light, the leaves of this species may grow to be nearly as large as a nickel.
 
The propagation of H. sibthorpioides poses no difficulties, as the individual plants often develop an abundance of side shoots.  This species will grow somewhat faster emerged outdoors or in a hydroponic setup during the summer (where its inconspicuous white flowers and green fruit frequently appear), so take the opportunity to increase your stock in this way if you need a large amount of additional shoots and have the required space.

H. sibthorpioides is well-suited to the fore- and midground areas of an aquascape.  The species looks best when it is intertwined among other foreground plants, where its unique gray-green coloration stands out. It can be maintained in larger stands, but quite a bit of pruning may be necessary to maintain an attractive appearance.  For the initial planting, simply weigh down a clump of plants with a few small stones in the middle of the area where you would like it to spread.  It may grow slowly at first, but it will gain speed in time, eventually necessitating regular trimming to prevent it from overtaking neighboring plants.