Eleocharis engelmannii
Family: Cyperaceae
Engelmann's spike-rush
Eleocharis engelmannii image
from USDA Plants website  
Eleocharis engelmannii 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: annual sedge