Rhynchospora

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  1a. Achenes 15–25 mm long including the 10–20 (–21) mm long tubercles; leaf blades 3–10 (–15) mm wide; style undivided or bifid only at tip
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    R. inundata

    2a. Stems not cespitose, produced from slender rhizomes, achene body 4–5 mm long; achene tubercle 10–15 mm long; spikes solitary or in clusters of 2–6
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    R. macrostachya

    2b. Stems cespitose, without rhizomes; achene body 5–6 mm long; achene tubercle (15–) 18–20 (–21) mm long; spikes mostly in dense clusters of 10–30
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  1b. Achenes 1–3 mm long including the 0.1–1.7 mm long tubercle; leaf blades 0.2–3 (–5) mm wide; style deeply bifid
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    3a. Plants annual; perianth bristles absent [Fig. 124]; inflorescences open, diffuse, cyme-like or panicle-like; spikes brown to nearly black, stalked
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      R. nitens

      4a. Tubercle depressed-triangular, 0.1–0.3 mm tall; achene body distinctly but irregularly transverse-rugose, with the marginal edges interrupted at the tubercle base
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      R. scirpoides

      4b. Tubercle narrow-triangular, 0.5–0.9 mm tall; achene body obscurely transverse-rugose, with the marginal edges flowing into the tubercle base
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    3b. Plants perennial; perianth bristles present (though sometimes caducous in 
 R. torreyana) [Figs. 122,123]; inflorescences of remote to congested clusters of spikes; spikes white to pale brown or red-brown to deep brown, usually clustered
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      5a. Perianth bristles retrorsely barbellate (smooth in rare forms of R. capillacea 
 and R. capitellata, antrorsely barbellate in rare forms of R. capitellata) [Fig. 122]; base 
of achene narrowed to a stipe-like process
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        R. alba

        6a. Flowers with 10–12 perianth bristles, these often antrorsely setose near base; floral scales white to light yellow-brown
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        6b. Flowers with 6 perianth bristles, without antrorsely oriented hairs at the base [Fig. 122]; floral scales pale brown to red-brown or deep brown
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          R. capillacea

          7a. Leaf blades filiform, 0.2–0.4 mm wide; spikes all ascending, in ovoid to ellipsoid clusters; achene body elliptic in outline, 1.5–2 mm long
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          R. capitellata

          7b. Leaf blades ± flat, 1.5–3 mm wide; basal spikes of each cluster spreading, 
the spikes in turbinate to hemispherical clusters; achene body obovate in outline [Fig. 122], 1.2–1.5 mm long
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      5b. Perianth bristles antrorsely barbellate (sometimes caducous, and therefore 
absent in fruit, in R. torreyana) [Fig. 123]; base of achene cuneate, not narrowed to a stipe-like process
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        R. fusca

        8a. Perianth bristles firmly attached to achene, reaching to base of tubercle or longer [Fig. 123]; tubercle (0.7–­) 1–1.3 (–1.5) mm long; achene bodies very finely transversely rugose (i.e., pattern not evident without high magnification)
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        R. torreyana

        8b. Perianth bristles weakly attached to achene, sometimes caducous, not extending more than ⅔ the length of achene body; tubercle 0.2–0.3 (–0.5) mm long; achene bodies finely transversely rugose with irregular horizontal ridges separated by intervals of narrow, vertical alveolae

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