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Key to Fimbristylis

Cyperaceae

Fimbristylis

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1 Style branches 3; achene trigonous or terete; plant an annual.
  2 Achene trigonous; spikelets linear-oblong to lanceolate, 3-7 mm long; ligule present, as a line of short, pale hairs
1 Style branches 2; achene lenticular or terete; plant an annual or perennial.
    3 Plants diminutive annuals, the culms 1-6 (-30) cm tall; leaf blades < 1 mm wide.
      4 Achene cylindrical, 2-4× as long as wide, curved like a tiny banana; inflorescence bracts 1-2 cm long
      4 Achene obovate, 1-1.5× as long as wide, not curved; inflorescence bracts 4-10 cm long.
        5 Inflorescence compact, the spikelets sessile or subsessile, in a dense cluster; base of style smooth or papillate
    3 Plants small to large annuals or perennials, the culms (6-) 15-150 cm tall; leaf blades > 1 mm wide.
          6 Spikelets 2-3 mm long; inflorescence compact, complexly glomerate; achenes obovoid; [of peninsular FL and s. TX in our area]
          6 Spikelets > 5 mm long; inflorescence at least partly diffuse, with spikelets stalked; achenes lenticular; [widespread in our area].
             7 Plant a medium-sized to robust perennial, the culms generally 5-15 dm tall, either cespitose, with a hardened base, and deeply set in the substrate, or rhizomatous, the rhizomes either slender or thick
               8 Plant cespitose, lacking rhizomes; bases of leaves hard, leathery, dark brown, deeply set in the substrate, the base of the plant generally 5-15 cm below the ground surface; achene (1.3-) 1.5-2 mm long
               8 Plant rhizomatous, the rhizomes either thick and knotty or slender and scaly (rarely with both); bases of leaves often somewhat thickened, hardened, and brownish, the base of the plant not especially deeply set; achene 0.8-1.2 (-1.3) mm long.
                 9 Plant a robust perennial to 15 (-20) dm tall, with elongate, slender, scaly, pale-to-reddish rhizomes (excavate carefully); leaves usually flat or keeled, 2-5 mm wide; stem usually flattened and scabrous-edged above; ligule present, a line of short, pale hairs
                 9 Plant a medium-sized perennial to 10 dm tall, rhizomatous, the rhizomes either short, thick, and knotty or also with slender rhizomes); leaves usually involute, ca. 1 mm wide; stem usually terete or oval in cross-section, smooth; ligule either absent or present.
                   10 Ligule present; sheaths and fertile scales glabrous; culm bases swollen, knotty, closely joined, forming short thick, knotty rhizomes; leaves and sheaths mostly glabrous; ligule present, mostly complete; involucral sheaths and fertile scales usually smooth.
                   10 Ligule absent or poorly developed; sheaths and fertile scales puberulent; culm bases not swollen, producing several slender, scaly, orange rhizomes; leaves and sheaths totally pubescent or glabrous; backs of involucral sheaths and fertile scales puberulent at least distally.
             7 Plant a small to medium-sized annual or perennial, the culms to 8 dm tall, neither rhizomatous (except F. brevivaginata) nor with a hardened base deeply set in the substrate.
                     11 Spikelets pale, usually solitary (-3) on the scape (and thus appearing somewhat like an Eleocharis)
(c) Spaulding, Dan - CC-BY-NC, permission granted to NCBG
                       12 Face (one side) of the achene with 15 or more longitudinal rows of rounded pits, the achene margin noticeably paler
(c) Horn, Jay
                       12 Face (one side) of the achene with 13 or fewer longitudinal rows of rectangular pits, the achene margin not noticeably paler.
                          13 Plant a perennial; leaves spreading, 2-5 mm wide; achenes lacking warts.
(c) Milly, Gemma C.
                            14 Plant bulbous at base, and also with scale-covered short rhizomes; spikelet scales glabrous or puberulent; [plant a rare native of rock outcrops in GA and AL]
(c) Horn, Jay
(c) Horn, Jay
                            14 Plant neither bulbous nor rhizomatous; spikelet scales glabrous; [plant weedy, probably introduced in North America]
                          13 Plant an annual; leaves spreading or ascending, 1-4 mm wide; achenes with or without warts.
(c) Ward, Scott G - CC-BY
                              15 Achenes lacking warts or with warts scattered over the entire surface; primary rays of umbel spreading or ascending, the inflorescence generally longer than broad; leaves relatively soft
                              15 Achenes with a few low warts on the edges; primary rays of umbel stiffly spreading (even deflexed), the inflorescence therefore often as broad as long or broader; leaves relatively hard, broad (averaging 2 mm wide), and spreading subdistichously