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| 1 Apex of sheath thin, membranous, hyaline, often with a torn edge. |
| ..2 Culms 0.1-0.3 mm in diameter; achenes whitish to pale brown; leaf sheaths of the upper culm closely sheathing the stem, not wrinkled, the apex acute |
| ..2 Culms 0.3-0.6 mm in diameter; achenes rufous- or olivaceous-brown to black; leaf sheaths of the upper culm usually prominently wrinkled, inflated, membranous, and disintegrating. |
| ....3 Achenes rufous-brown to reddish-purple to black, (0.3-) 0.4-0.6 mm wide; longer bristles retrorsely barbed, shorter than to equaling achene body |
| ....3 Achenes olivaceous-brown to black, 0.5-0.7 (-0.8) mm wide; longer bristles either retrorsely barbed and equaling to exceeding the tubercle, or smooth and shorter than the tubercle. |
| ......4 Bristles retrorsely barbed, the longer equaling to exceeding the tubercle; [wet sandy or peaty habitats, widespread] |
| ......4 Bristles smooth, the longer shorter than the tubercle; plants of [tidal rivers, in s. NJ] |
| 1 Apex of sheath firm, somewhat thickened, opaque, with a definite edge. |
| ........5 Rhizomatous perennials growing from thick horizontal rhizomes. |
| ..........6 Basal (sterile) scales 2-3, the lowest not encircling the base of the spike; [of the Mountains, rarely the Piedmont] |
| ..........6 Basal (sterile) scale solitary and spathiform, encircling the base of the spike; [of either the Mountains, upper Piedmont, or outer Coastal Plain]. |
| ............ 7 Achenes prominently reticulate-pitted; [of the outer Coastal Plain] |
| ............ 7 Achenes smooth to faintly reticulate; [of the Mountains, rarely Piedmont, or outer Coastal Plain]. |
| ............ ..8 Culms slender to filiform; scales obtuse, 30-40 per spike; [of basic soils, of the Mountains and rarely Piedmont] |
| ............ ..8 Culms thicker, somewhat inflated; scales acute, 5-30 per spike; [of brackish habitats of the outer Coastal Plain] |
| ........5 Tufted or cespitose annuals without thick horizontal rhizomes. |
| ............ ....9 Tubercle nearly or actually as broad as the achene, and appearing confluent with it, broader than high. |
| ............ ......10 Tubercle flat-deltoid, 1/4 as high as the achene; bristles shorter than the achene body; [plants of clay soils only] |
............ ......10 Tubercle short-conic, 1/3-1/2 as high as the achene; bristles much exceeding the tubercle; [plants of a variety of soils] |
| ............ ....9 Tubercle < 2/3 as broad as the achene, conic, taller than broad. |
| ............ ........11 Achene body pale brown, about 1 mm long |
| ............ ........11 Achene body black, 0.5-1.0 mm long. |
| ............ ..........12 Spikes lance-ovoid to subcylindric; achene body -.5-0.6 mm long |
| ............ ..........12 Spikes ovoid to subglobose; achene body 0.7-1.0 mm long |