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Key to Rhynchospora, Key E: beaksedges with bristles smooth, or antrorsely barbed and filiform,
or absent, the achene surface smooth, minutely pitted, or finely striate
[subgenus Diplostylae; sections Chapmaniae, Fasciculares, and Fuscae]

Cyperaceae

Rhynchospora

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1 Bristles 12; [section Fasciculares]
1 Bristles 6 or fewer.
  2 Leaves with a short taper at the tip, blunt to acute, but not long-acuminate; achene surface minutely pitted near the margin; [section Chapmaniae].
    3 Basal leaves 4-6 mm wide, ciliate, rosulate; scales acuminate, the midrib ciliate; bristles 6, < ½ the length of the achene; achenes 1.6-2 mm long; [widespread in mesic to wet pinelands from VA s. to FL, w. to e. LA]
    3 Largest basal leaves 2.5-3 mm wide, eciliate, not rosulate; scales aristate, the midrib eciliate; bristles 3-4, 1 or more equaling or exceeding the tubercle; achenes (1.4-) 1.5-1.7 (-1.9) mm long; [rare, s. GA, disjunct in se. SC]
  2 Leaves long-acuminate at the tip; achene surface smooth or finely striate.
      4 Bristles absent or 1-3 rudimentary; scales white to pale tan (or pale reddish-brown in R. brachychaeta); [section Chapmaniae].
        5 Inflorescence composed of (1-) 2-3 turbinate to ellipsoid clusters; spikelets pale reddish-brown, (2.7-) 3-3.5 mm long; achenes usually 2 per spikelet
        5 Inflorescence composed of 1 (-2) hemispheric to broadly turbinate cluster(s); spikelets white to pale brown, either 2-2.5 (-3) mm or (3.5-) 4-5.5 mm long; achenes 1 per spikelet.
          6 Base of plant not bulb-like, not enclosed in bladeless sheaths; spikelets 2-2.5 (-3) mm long; achene 1.0-1.2 mm long, 0.8-1.0 mm wide
          6 Base of plant bulb-like, enclosed in bladeless sheaths; spikelets (3.5-) 4-5.5 mm long; achene 1.4-1.8 mm long, 1.2-1.5 mm wide
      4 Bristles present (if rudimentary, then 4-6); scales tan, pinkish-tan, rufous, or brown.
             7 Achene 0.6-1.1 mm wide, pyriform, obovoid, or narrowly elliptic, pale to dark brown but not blackish; tubercle margin setose (except R. setosa).
               8 Inflorescence of 1 cluster; tubercle 0.3-0.4 mm long, the margin smooth; [s. MS Coastal Plain; section Chapmaniae]
               8 Inflorescence of (1-) 2-4 (-10) clusters; tubercle 0.4-1.4 mm long, the margin setose; [widespread; section Fuscae].
                 9 Achene narrowly elliptic or narrowly obovoid, 1.2-1.5 mm long by 0.6-0.7 mm wide, twice as long as wide; tubercle 0.8-1.2 mm long
                 9 Achene broadly elliptic to obovoid or pyriform, < 2× as long as wide; tubercle 0.4-1.5 mm long.
                   10 Leaves 2-4 (-5) mm wide; stipe subtending achene 0.5-1.0 mm long
                   10 Leaves 0.2-1.5 (-2) mm wide; stipe subtending achene < 0.4 mm long.
                     11 Leaves to 1.5 (-2) mm wide; achene 1.0-1.7 mm long, 0.9-1.1 mm wide; tubercle 0.5-1.5 mm long, triangular-subulate, the margins typically conspicuously concave.
                       12 Culms solitary to loosely cespitose by slender rhizomes; terminal internode straight; clusters turbinate to ovoid; achene 1.0-1.3 mm long, uniformly medium to dark brown; tubercle 0.7-1.5 mm long; bristles usually of two lengths, some equaling the tubercle, and some equaling or shorter than the achene
                       12 Culms solitary to cespitose, without slender rhizomes; terminal internode often arched; clusters corymbose to hemispheric; achene 1.3-1.7 mm long, pale to reddish-brown, often translucent centrally, with a distinctly thickened wire-like margin; tubercle 0.5-1.0 mm long; all bristles more-or-less equaling the tubercle
                     11 Leaves filiform, < 1 mm wide; achene 0.8-1.3 mm long, 0.6-0.9 mm wide; tubercle 0.4-0.8 mm long, deltoid to triangular-subulate, the margins flat to concave.
                          13 Plants with delicate, long-creeping rhizomes; spikelets 5-7 mm long; achene uniformly opaque; tubercle 0.6-0.8 mm long
                          13 Plants without rhizomes; spikelets 2.5-5 mm long; achene translucent centrally; tubercle 0.4-0.7 mm long.
                            14 Achenes 1.5-1.9 mm long, 0.5-0.8 mm wide; stipes 0.2-0.3 mm long; tubercles 0.4-0.6 mm long
                            14 Achenes 2.1-2.3 mm long, 0.8-0.9 mm long; stipes 0.3-0.4 mm long; tubercles 0.6-0.7 mm long
             7 Achene > 1 mm wide (except 0.8 mm wide in R. fernaldii with a blackish surface), suborbicular or broadly ellipsoid; tubercle margin smooth or roughened but not setose; [section Fasciculares].
                              15 Achene 1.3-4.2 mm long, 1.1-3.6 mm wide, brown to dark brown.
                                  17 Leaves 2-4 mm wide; achene light to dark brown, usually at least somewhat rugulose in texture, 2.0-2.7 mm long, 2.0-2.5 mm wide, the tubercle base often somewhat rimmed
                                  17 Leaves 4-8 mm wide; achene blackened (when fully ripe), shiny and smooth in texture, 3.0-4.2 mm long, 3.0-3.6 mm wide, the tubercle base usually not rimmed (grading more smoothly between the dark achene body and lighter-colored tubercle
                                         20 Larger leaves to 1 mm wide; mature culms to 4.5 dm long; floral fascicles 1 (-2); tubercle 0.2-0.5 mm long
                                         20 Larger leaves 2-4 mm wide; mature culms to 13 dm long; floral fascicles (1-) 2-4; tubercle 0.4-0.7 mm long
                                           21 Basal leaves filiform to (rarely)1.3 mm wide, the longer approaching length of culm; tubercle narrowed above the base into a strap-like beak
                                             22 Longer bristles < ½ as long to exceeding achene body; achene suborbicular, 1.2-1.5 mm wide; tubercle triangular; larger basal leaves 2-4 mm wide