Eleocharis ovata (Roth) Roem. & Schult.
Family: Cyperaceae
oval spike-rush
[Eleocharis annua House,  more...]
Eleocharis ovata image
from USDA Plants website  
Eleocharis ovata image
University of Wisconsin-Stevens Point, Robert W. Freckmann Herbarium (UWSP)  
Etymology: Eleocharis: Greek elos for "marsh" and charis for grace, referring to marsh plant
Plants: erect, annual sedge