Eleocharis parvula

Eleocharis parvula is a species of spikesedge known by the common names dwarf spikerush, small spikerush and hairgrass in aquaria. It is a plant of brackish and saltwater habitat, such as marshes and mudflats. It is a perennial herb growing tufts of spongy, compressible stems not more than 10 centimeters tall. The plant grows from a tuber which is J-shaped or horseshoe-shaped, a characteristic that helps in the identification of the species. The inflorescence is an oval-shaped spikelet just 2 or 3 millimeters long, made up of several tiny flowers....read more on Wikipedia.