Small leafy sedge carpeting the dry bed of Y Swamp, which I have seen it do in other areas too, during drought. Under the microscope the most distinctive feature of this thing is its hairy nuts! The base of the style is ciliate, giving it a little tuft of hairs at the top end of the nut. The zigzag stems where the nuts and glumes have fallen are also rather distinctive, and the fact that the involucral bracts are shorter than the inflorescence branches (2nd photo).