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KEY A: Subkey in Juncus

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1 Flowers borne in heads (glomerules) of 2-6 flowers per head; leaves spine-tipped; single bracteole subtending glomerule present at base of pedicel; [plants of brackish habitats]; [subgenus Juncus, section Juncus]
..2 Capsule 3.5-5 mm long, obviously longer than the tepals
..2 Capsule < 3.5 mm long, shorter than or nearly equaling the tepals
....3 Capsule length nearly equal to perianth length; seeds tailed; [historically known only from Kings County, NY; no longer persisting]
....3 Capsules distinctly shorter than perianth length; seeds not tailed; [common in coastal marshes; MD s. to FL, w. to TX]
1 Flowers borne singly on branches of inflorescence; leaves not spine-tipped; each flower subtended by two bracteoles in addition to bracteole at base of pedicel; [plants of various habitats].
......4 At least a few sheaths at base of plant with well developed blades; inflorescence bract channeled on one side; [subgenus Agathryon, section Steirochloa]
......4 Sheaths at base of plant bladeless; bract not channeled; [subgenus Agathryon, section Juncotypus].
........5 Culms well spaced along creeping rhizomes.
..........6 Anthers longer than filaments
..........6 Anthers shorter than filaments.
............ 7 Rhizomes 1.5-2 mm diameter; culms 1 mm diameter; inflorescence 3-12 flowered; [boreal, south to ne. WV]
............ 7 Rhizomes 2-4 mm diameter; culms 1.5-2.5 mm diameter; inflorescence 8-30+ flowered; [from NC and TN south to Panhandle FL]
........5 Culms cespitose or tufted on short branching rhizomes.
............ ..8 Perianth much shorter than capsule (about ½ as long); stamens 6; [from NC and TN south to Panhandle FL]
............ ..8 Perianth > 3/4 length of capsule; stamens 6 or 3; [collectively widespread].
............ ....9 Capsules 3-4 mm long; stamens 6; [rare alien in piedmont and mountains of VA]
............ ....9 Capsules 1.5-3.2 mm long; stamens 3; [widespread native].
............ ......10 Stems with 10-20 prominent ridges just below the inflorescence, with a firm texture; fresh upper stems dull or matte; dried stems coarsely ridged, ridges visible in high relief at 10×, dried ridges capped with shiny bulging cells; perianth 2.7-3.6 mm long, sepals slightly exceeding the petals and capsule.
............ ........11 Inflorescence bract sheathes swollen and dilated at the base of the inflorescence; inflorescence bract often reflexed after fruit ripening; sheath bases of leaves on the lower stem warm reddish-brown to brown; infructescences capitate, occasionally lobed; [introduction in few sites in our region]
............ ........11 Inflorescence bract sheathes narrow and not swollen; inflorescence bract erect after fruit ripening; sheath bases of leaves on the lower stem usually purplish-black, occasionally dark red-brown; infrustescences usually open, diffuse; [widespread native]
............ ......10 Stems with 25-30 relatively inconspicuous ridges just below the inflorescence, with a soft texture, easily compressed; fresh upper stems shiny; dried stems with lower ridges, fine or coarse, ridges visible in low relief at 10×, dried ridges capped with low dull cells; perianth 1.9-2.8 mm long, the sepals equaling the petals.
............ ..........12 Tepals soft, spreading or curving away from capsule at maturity; leaf sheaths 6-14 cm long, usually dark margined, clasping the stem
............ ..........12 Tepals hard, tightly appressed to capsule at maturity; leaf sheaths (11-) 15-27 cm long, lacking dark margin, often not clasping the stem
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