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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

Key to Rhynchospora, Key F: beaksedges with bristles smooth, or antrorsely barbed and filiform, or absent,
the achene surface transversely ridged, rugose, or honeycombed-reticulate
[subgenus Diplostylae; sections Globulares, Harveyae, Mixtae, Psilocarya, Pusillae, Rariflorae]

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1 Bristles absent (or apparently so at 10×); achene 0.5-0.7 mm wide; tubercle 0.1-0.2 mm long, skull-cap like; [section Pusillae].
  2 Achene including tubercle 1.0-1.2 mm long, the achene surface evidently reticulate and obscurely transversely ridged, the body ellipsoid; bristles present, white, barely visible at 20×, the longest shorter than the achene body
  2 Achene including tubercle 0.6-0.9 mm long, the body obovoid; bristles absent.
    3 Achene surface smooth, faintly reticulate, not transversely ridged
    3 Achene surface rough, distinctly transversely ridge
1 Bristles present or absent; if absent, then the achene > 1 mm long or > 0.7 mm wide, and tubercle triangular to subulate.
        5 Achene including tubercle 1.0-1.2 mm long; tubercle minute, skullcap-like; [section Pusillae]
        5 Achene including tubercle 1.5-2.9 mm long; tubercle triangular to triangular-acuminate; [section Rariflorae].
          6 Bristles subequaling to exceeding the tubercle; tubercle 0.75-1.4 mm long
          6 Bristles shorter than the achene body; tubercle 0.3-1.0 mm long.
             7 Achene 1.3-1.6 mm long, 0.9-1.4 mm wide; tubercle 0.3-0.6 (-0.75) mm long; bristles 1/3-1/2(-4/5) as long as achene body
             7 Achene 1.6-1.8 mm long, 1.35-1.5 mm wide; tubercle 0.6-1.0 mm long; bristles 2/3 to nearly as long as achene body
      4 Culms stouter; leaves wider, not filiform.
               8 Achene faces flat or concave; when one face is concave, the opposite face is sometimes slightly convex (slightly biconvex R. decurrens and R. microcarpa are keyed here for convenience).
                 9 Achene at least twice as long as wide, elliptic-oblong; tubercle subulate, 0.8-1.2 mm long; [section Mixtae]
                 9 Achene < twice as long as wide, obovate; tubercle triangular, 0.2-0.9 mm long.
                     11 Achene ±2.2 mm long, ±1.8 mm wide; tubercle ±0.9 mm long; [section Globulares]
                     11 Achene 0.8-1.2 mm long, 0.7-1.2 mm wide; tubercle 0.2-0.5 mm long; [section Mixtae].
                       12 Larger leaves (3-) 4-6 mm wide; bristles exceeding tubercle; achene faces flattened
                       12 Larger leaves 1-3 (-4) mm wide, bristles half as long as achene to equaling tubercle; achene faces slightly convex
                   10 Longer bristles shorter than to equaling achene body, or absent.
                          13 Larger leaves 3-5 mm wide; achene 1.4-1.6 mm wide; tubercle 0.6-0.8 mm long, abruptly rising from a flaring basal collar; [section Globulares]
                          13 Larger leaves 1-3 (-4) mm wide; achene 0.7-1.3 mm wide; tubercle 0.15-0.5 mm long, without a flaring basal collar; [section Mixtae].
                              15 Culms 20-50 cm long; leaves 1-2 mm wide; bristles ½ or less as long as achene body
                              15 Culms 50-110 cm long; leaves (1-) 2-4.5 mm wide; longer bristles more than ½ as long to exceeding achene body.
                                16 Achene 1.3-1.8 mm long, 0.9-1.2 mm wide, the faces flat with 10-12 transverse ridges
                                16 Achene 0.8-1.4 mm long, 0.7-1.2 mm wide, the faces slightly biconvex with 6-12 transverse ridges.
                                  17 Clusters elongate; achene 1.0-1.4 mm long, 0.8-1.0 mm wide, narrowly obovate to elliptic, averaging 8-12 transverse ridges; most tubercle bases convexly seated on the achene summit and somewhat decurrent along the achene margins, the tubercle surface often whitish-waxy
                                  17 Clusters usually compact; achene 0.8-1.2 mm long, 0.7-1.2 mm wide, suborbicular to elliptic, averaging 6-7 transverse ridges; most tubercle bases flat across the achene summit, not decurrent, the tubercle surface usually dark, not waxy
                                    18 Achene 1.4-4.2 mm long, 1.2-3.6 mm wide, the summit with a thickened bony to crustaceous rim surrounding the base of the tubercle; [section Harveyae].
                                       19 Achene tumid, lightly pitted or cancellate in a honeycomb pattern, 1.5-4.2 mm long, 1.4-3.6 mm wide.
                                    18 Achene 0.7-1.8 mm long, 0.7-1.5 mm wide, the summit without a textured rim surrounding the base of the tubercle (if the base of the tubercle is rim-like, then it is distinguished from the summit of the achene by a constriction or articulation).
                                                 24 Spikelets (5-) 6-10 mm long, tan or brown, with an acuminate tip; tubercle ends upturned away from the achene at about a 90 degree angle
                                             22 Bristles present (occasionally detached in R. decurrens and R. miliacea with achenes 1.0-1.4 mm long); achene 0.8-1.9 mm long.
                                                      26 Cluster branches flexuous (the branches curved), not uniformly erect and stiff; bristles one-half as long to equaling the achene (or longer in R. microcarpa); [section Mixtae].
                                                        27 Clusters elongate; spikelets 2.5-3.5 mm long; achene narrowly obovate to elliptic, averaging 8-12 transverse ridges; most tubercle bases convexly seated on the achene summit and somewhat decurrent along the achene margins, the tubercle surface often whitish-waxy
                                                        27 Clusters usually compact, branches ascending to spreading (sometimes widely so in R. vernalis); spikelets 1.5-3.0 mm long; achene suborbicular to elliptic, averaging 5-8 (-9) transverse ridges, most tubercle bases flat across the achene summit, not or only slightly decurrent, the tubercle surface usually dark, not waxy.
                                                          28 Inflorescence occupying the upper 2/3-3/4 of the length of the culm, the lowest lateral panicle at the first or second node above the base; spikelets 1.5-2.25 mm long, broadly ovoid to suborbicular, apically rounded; achene body averaging 5-6 (-7) horizontal ridges; tubercle 0.2-0.4 mm long
                                                          28 Inflorescence occupying the upper ¼-½ of the culm, the lowest 2-4 nodes barren; spikelets 2.0-3.0 mm long, ovoid, acute; achene body averaging 6-9 horizontal ridges; tubercle 0.25-0.85 mm long.
                                                            29 Inflorescence cluster branches ascending, the clusters mostly tightly congested; achene 1.0–1.7 times as long as wide, dark brown, shallowly nearly horizontally ridged or with nearly isodiametric alveolae, ridges 7–9; bristles of each achene nearly equal in length, from 0.5 to 1.5 times as long as the achene body; plants slender, mostly less than 1 meter tall, with leaves typically less than 40 cm long and 3 mm wide; [NC s. to s. FL, w. to s. MO and s. TX]
                                                            29 Inflorescence cluster branches widely spreading in flower, spreading to ascending in fruit, the clusters rather open, not congested; achene 1.0–1.2 times as long as wide, light brown, strongly transversely ridged with 6–8 irregular ridges and narrow rectangular alveolae; bristles unequal in length, from 0.9–1.5 times as long as the achene body; plants robust, typically more than 1.2 meters tall, with leaves often over 50 cm long and 4 mm wide; [FL]
                                                                 31 Larger culm leaves to 5 mm wide; achenes (1.2-) 1.4-1.6 (-1.9) mm long, (1.1-) avg. 1.4 (-1.75) mm wide; achene surface alveoli longitudinally narrow; tubercle 0.3-0.7 mm long, base 0.6-1.0 mm wide
                                                                 31 Larger culm leaves to 3 mm wide; achenes (1.0-) avg. 1.3 (-1.5) mm long and wide; if achene surface alveoli longitudinally narrow, then tubercle 0.2-0.4 mm long and base 0.5-0.7 mm wide (R. globularis).
                                                                   32 Longer bristles ⅓-½ (-¾)× the length of the achene; achene surface alveoli longitudinally narrow (typically 0.02-0.05 mm wide between the longitudinal walls), the latitudinal walls raised into horizontal ridges; tubercle 0.2-0.4 mm long, the base 0.5-0.7 mm wide
                                                                   32 Longer bristles ⅔-1× the length of the achene; achene surface alveoli nearly as wide as long (typically 0.05-0.1 mm wide between the longitudinal walls), the latitudinal walls obscurely or not at all raised into horizontal ridges; tubercle 0.35-0.7 mm long, the base 0.7-0.9 mm wide
                                                                     33 Primary branches of the inflorescence spreading at right angles from the culm, each spikelet or small cluster on slender spreading or reflexed stalks; [section Mixtae]
                                                                       34 Spikelets < 5 mm long; achene (body) 1.0-1.5 (-1.6) mm long (if ≥ 1.4 mm long, then the achene stipe either absent (R. saxicola) or the stipe ≤ 0.3 mm (R. caduca); [section Mixtae, except R. saxicola in section Globulares].
                                                                           36 Achene slenderly obovoid, 0.8-1.0 mm wide, latitudinal alveoli walls weakly or not at all raised into transverse ridges; achene stipe diminuitive or virtually absent
                                                                                38 Inflorescence occupying the upper 2/3-3/4 of the length of the culm, the lowest lateral panicle at the first or second node above the base; spikelets 1.5-2.25 mm long, broadly ovoid to suborbicular, apically rounded; achene body averaging 5-6 (-7) horizontal ridges; tubercle 0.2-0.4 mm long
                                                                                  39 Inflorescence cluster branches ascending, the clusters mostly tightly congested; achene 1.0–1.7 times as long as wide, dark brown, shallowly nearly horizontally ridged or with nearly isodiametric alveolae, ridges 7–9; bristles of each achene nearly equal in length, from 0.5 to 1.5 times as long as the achene body; plants slender, mostly less than 1 meter tall, with leaves typically less than 40 cm long and 3 mm wide; [NC s. to s. FL, w. to s. MO and s. TX]
                                                                                  39 Inflorescence cluster branches widely spreading in flower, spreading to ascending in fruit, the clusters rather open, not congested; achene 1.0–1.2 times as long as wide, light brown, strongly transversely ridged with 6–8 irregular ridges and narrow rectangular alveolae; bristles unequal in length, from 0.9–1.5 times as long as the achene body; plants robust, typically more than 1.2 meters tall, with leaves often over 50 cm long and 4 mm wide; [FL]