Some extracts from Wikipedia link (for pictures & more details, click on the link): http://en.wikipedia.org/wiki/Marsilea_quadrifolia
'Four Leaf Clover'; European waterclover (USA); Sushni in parts of India
found in central and southern Europe, Caucasia, western Siberia, Afghanistan, sw India, China, Japan and North America. Considered a weed in some parts of the United States where it has been well established in the north eastern States for over 100 years. 
Aquatic fern bearing 4 parted leaf resembling '4-leaf clover' (Trifolium). Leaves floating in deep water or erect in shallow water or on land. Leaflets obdeltoid, to 3/4" long, glaucous, petioles to 8" long; Sporocarp (ferns) ellipsoid, to 3/16" long, dark brown, on stalks to 3/4" long, attached to base of petioles.
A juice made from the leaves is diuretic and febrifuge. It is also used to treat snakebite and applied to abscesses etc. The plant is anti-inflammatory, diuretic, depurative, febrifuge and refrigerant. 
The plant prefers light (sandy) and medium (loamy) soils. The plant prefers acid, neutral and basic (alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It requires moist or wet soil and can grow in water. 
Marsilea quadrifolia can be grown as a potted plant, either just with soil kept wet, or semi-submerged, with fronds emergent from the water, or fully-submerged, with the fronds floating on the surface of the water.
In the aquarium, water clover is grown fully submerged, usually in the foreground where it spreads by means of runners. It normally seems to be unfussy as to light and water conditions, and doesn't need a rich substrate.
Marsileas are very easy to germinate from their Sporocarp (ferns). However, the sporocarps must be abraded, cracked, or have an edge sliced off before submerging them in water so that the water can penetrate to swell the tissues, and germination is infrared-light dependent. Full sunlight is fine for this purpose.