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1 Scales awned or cuspidate, cusp 0.3-0.5 mm long, excurved; achenes 0.6 mm long; [section Pumili]
..2 Floral scales divaricate (thus the spikelet margin appearing coarsely dentate), with whitish or hyaline margins; coarse, erect plants 30-75cm tall, inflorescence diffuse; [section Albomarginati]
......4 Scales 2.5-3.6 mm long, 1.6-1.8 mm wide; achenes 1.2-1.6 mm long, 0.6-0.9 mm wide, narrowly obovoid; [beaches, maritime habitats]
........5 Cespitose annual, < 12 cm tall; floral scales ovate, 1.3-1.6 mm long, loosely imbricate; styles 0.1-0.2 mm long; stigmas 0.3-0.4 mm long; filaments 1.2-1.4 mm long; anthers 0.1-0.2 mm long; achenes stipitate, strongly compressed laterally; [LA and westwards, rare]
........5 Shortly rhizomatous perennial, mostly > 12 cm tall; floral scales oblong, 1.8-2.4 mm long, closely imbricate; styles 0.6-1 mm; stigmas 1.4-2 mm long; anthers 0.6-0.8 mm long; achenes substipitate to cuneate, slightly compressed laterally; [widespread]
..........6 Achenes black to dark reddish brown, with encrusted transverse whitish lines, epidermal cells longitudinally elongate, rectangular; scales pale brown or yellowish, the dark achenes strongly contrasting and visible through the spikelets in life (without backlighting); fibrous-rooted annuals; [section Zonati].
............ ..8 Anthers ellipsoid, 0.3-0.6 mm long; spikelets 1.8-3 mm wide, with scales 1.8-2.6 mm long; achenes brown, ellipsoid, ovoid, or obovoid, 0.4-0.8 mm wide; [more widespread]
............ ..8 Anthers linear, 2-2.4 mm long; spikelets 3-5 mm wide, with scales (3.6-) 3.8-4.2 (-4.6) mm long; achenes black, broadly obovoid to orbiculate, 0.8-1 mm wide; [s. peninsular FL, rare waif]
............ ....9 Floral scales firmer, subcoriaceous, not bilaterally sulcate; reddish pigmentation ±uniformly distributed or concentrated basally and medially; floral scales 2.5-3 mm long; annuals, culms usually <25 (35) cm long
............ ......10 Cespitose annuals, culms usually < 25 (-35) cm tall; stamens 2; style divided nearly to base; style branches conspicuously exserted beyond floral scale, exposed portions about as long as floral scale
............ ......10 Rhizomatous perennials, culms usually > 25 cm tall; stamens 3; style divided less than half its length; style branches not so conspicuously exserted, exposted portions less than half as long as floral scale