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..2 Inflorescence bracts widened abruptly at its base, the widened portion prominently fimbriate-pectinate; perennial, culms 10-50 cm tall; achene 1-1.3 mm long, white or yellowish, the apex retuse (the three lobes projecting beyond and surrounding the tubercle)
....3 Inflorescence bracts numerous and conspicuous, several much exceeding the cluster of spikelets; achenes 0.8-1.2 mm long, transversely rugose; spikelet scales usually greenish or pale brown, dull, puberulent
....3 Inflorescence bracts few and inconspicuous, none or sometimes one exceeding the cluster of spikelets (and then only slightly); achenes 0.5-0.6 mm long, finely reticulate; spikelet scales usually reddish-brown, lustrous, smooth or nearly so
........5 Achenes rugose; plants with a soft base, annual; anthers ca. 0.6 mm long; [collectively widespread]
........5 Achenes rugulose and also papillate; plants with a hardened base, perennial; anthers ca. 1 mm long; [e. TX westwards and southwestwards]
..........6 Annual, to 1-2 (-3) dm tall; inflorescence a simple (rarely compound) umbel of few (3-9) lance-ovoid spikelets; longest involucral bract seldom exceeding the inflorescence; leaf margins usually hispidulous
..........6 Perennial, to 1.5-4 dm tall; inflorescence a compound (rarely simple) umbel of many (8-30) oblong or lance-linear spikelets; longest involucral bract commonly exceeding the inflorescence; leaf margins usually distinctly tuberculate-scabrid