1 Mature leaves broader, to ca. 1.5 cm wide; inflorescence a long, slender raceme, often with > 5 clusters of spikelets; plants tall, often > 1 m; [non-native; s. FL]

1 Mature leaves thinner (or reduced to sheaths), typically < 1 cm wide; inflorescence terminal or racemose, typically with < 5 clusters of spikelets; plants shorter, < 1 m tall; [collectively widespread].

..2 Sheaths of leaves glabrous, the largest leaf blades 0-2 (-5) cm long; plant strongly rhizomatous, the culms usually spaced about 10 cm apart.

....3 Blades of culm leaves < 5 cm long; spikelets mostly lance-ovoid, sessile in terminal clusters and also often with additional sessile or peduncled clusters lower on the culm; involucral bract longer than the spikelets

....3 Blades of culm leaves essentially reduced to sheaths, or very short (< 0.5 cm long); spikelets mostly ovoid, sessile in terminal clusters; subtending involucral bract shorter than the spikelets

..2 Sheaths of leaves sparsely to densely hirsute, the largest leaf blades 5-20 cm long; plant more-or-less cespitose, annual or perennial, if perennial the rhizomes short and scaly or cormlike, the culms usually arising together.

......4 Perianth bristles no longer than the achene stipe (not nearly reaching halfway up the achene body), without barbs (sometimes very finely toothed, the teeth ascending); blades of the perianth scales with a blunt or short-apiculate apex

......4 Perianth bristles longer than the achene stipe, reaching the middle of or exceeding the achene body, strongly and retrorsely barbed (if smooth as in F. bushii, then scales of the spikelets also with strongly retrorse apical cusps); blades of the perianth scales with an acuminate to awned apex.

........5 Plants perennial, the rhizomes scaly or elongate and slender; anthers 0.9-1.3 mm long.

..........6 Upper leaf sheaths glabrous; perianth blades typically bearing a subapical bristle; perianth blades rounded or retuse, rarely acute; rhizomes without corm-like buds

..........6 Upper leaf sheaths pubescent; perianth blades lacking a subapical bristle; rhizomes with corms or corm-like buds or shoots present; perianth blades acute to acuminate.

............ 7 Perianth bristles retrorsely barbed, reaching perianth blade base or beyond; scales of the spikelets with 3-5 (-7) lower ribs, the apical cusp 1/2-1x the length of the scale; [MA s. to FL, w. to c. TX]

............ 7 Perianth bristles mostly smooth and shorter than perianth blades; scales of the spikelets with 3 prominently raised medial ribs, the apical cusp ≥ the length of the scale; [s. AR s. to LA, w. to se OK and e. TX]

........5 Plants annual, not bearing scaly rhizomes; anthers ca. 0.5 mm long.

............ ..8 Blades of the perianth scales acuminate, narrowed into an awn (the awn without barbs)

............ ..8 Blades of the perianth scales rounded, retuse, or rarely acute at the tip, bearing a subapical bristle which is retrorsely barbed