1. Culms terete or several-ridged, smooth; anthers 1.1-2.5 mm long (not including a short prolonged tip); body of achenes 1.5-1.7 mm long.

T. cespitosum

1. Culms 3-angled, scabrous; anthers 0.6-1.1 mm long; achenes various.

2. Perianth bristles ciliate, slightly or not at all exceeding the blunt achene; scales of spikelet not more than 7; achenes ca. 1.6-1.8 mm long.

T. clintonii

2. Perianth bristles smooth, several times as long as the apiculate achene at maturity; scales of spikelets slightly more than 7; body of achene less than 1.5 mm long.

T. alpinum