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1 Leaves with smooth or slightly scabrous margins; spikelets glabrous or nearly so; [of salt to brackish coastal marshes]; [section Spartina; subsection Alterniflori]
....3 Spikes (6-) 15-75 per inflorescence, tightly appressed; leaves 1.5-4.5 mm wide, strongly involute; [section Spartina; subsection Ponceletia]
......4 Upper glumes 3-4-veined; [native, SC to s. FL, west to e. TX]
......4 Upper glumes 1-veined; [alien, e. TX]
........5 Spikes 1-9 per inflorescence; culms 0.5-1 m tall; leaves 0.5-4 (-7) mm wide, usually involute when fresh
..........6 Second glume acute, not awned; first glume averaging ca. 1/2 as long as the lemma; spikes (6-) 20-50 (-more) per inflorescence; [of fresh to brackish coastal marshes]
..........6 Second glume with an awn 3-10 mm long; first glume averaging ca. 7/8 as long as the lemma; spikes (5-) 7-27 per inflorescence; [of fresh marshes, either inland or coastal]