A quote from "Flora of the A.C.T." Nancy T. Burbidge & Max Gray: "the uppermost leaf sheath thickened, truncate and mucronate at orifice". Mucronate means "ending with a stiff point". The Sample Photos show this feature, which is diagnostic of the species. The drawing below is from that book.
Eleocharis acuta is listed in the following regions:
Canberra & Southern Tablelands | Albury, Wodonga | South Coast | Far West New South Wales | Loddon Mallee