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Key to Eleocharis, Key E: spikerushes with achenes lenticular or biconvex and styles mostly 2-branched (2-fid)

Cyperaceae

Eleocharis

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1 Distal leaf sheath apex delicate, membranous, or disintegrating (thus, sometimes not readily apparent); usually inflated or wrinkled, often with a torn edge; culms 0.1-0.6 (to 1 mm on fresh specimens) mm wide.
  2 Culms 0.1-0.3 mm in diameter; achenes whitish to pale brown; leaf sheaths of the upper culm closely sheathing the stem, not wrinkled, the apex acute
  2 Culms 0.3-0.6 mm in diameter; achenes rufous- or olivaceous-brown to black; leaf sheaths of the upper culm usually prominently wrinkled, inflated, membranous, and disintegrating.
    3 Achenes rufous-brown to reddish-purple to black, (0.3-) 0.4-0.6 mm wide; longer bristles retrorsely barbed, shorter than to equaling achene body
    3 Achenes olivaceous-brown to black (often olivaceous), 0.5-0.7 (-0.8) mm wide; longer bristles either retrorsely barbed and equaling to exceeding the tubercle (E. olivacea var. olivacea), or smooth and shorter than the tubercle (E. olivacea var. reductiseta).
      4 Bristles retrorsely barbed, the longest bristles equaling to far exceeding the tubercle; [wet sandy or peaty habitats, NS to FL, w. to MS and TX]
      4 Bristles smooth, the longest bristles shorter than the tubercle; [tidal rivers, in s. NJ]
1 Distal leaf sheath apex firm, opaque, somewhat thickened, with an acute to obtuse apex, and sometimes bearing a small tooth; rarely disintegrating, not inflated or wrinkled; culms 0.3-5 mm wide.
        5 Rhizomatous perennials growing from evident horizontal rhizomes; achenes not persistent in the spikelet after scales have fallen, 0.9-1.9 mm long; tubercles pyramidal or mammillate (nipple-like); [E. palustris complex].
          6 Basal (proximal) scale of spikelet encircling 2/3-3/4 of the culm; culms terete to markedly compressed; (rarely amplexicaulous in E. macrostachya, if so then culms also usually markedly compressed).
             7 Basal 2-3 scales empty or fertile; spikelets 5-40 mm long, 2-5 mm wide; achene yellow, yellow-brown, or dark-brown; leaf sheath apex often with tooth (except E. macrostachya); [primarily west of MS river, with very scattered locations eastward]
               8 Culms terete or slightly compressed; distal leaf sheath apex often obtuse, rarely with a tooth present (if so to 0.1 mm); spikelets broadly lanceoloid to ovoid, the scales 3.5-4.0 (-4.5) long; achenes 1.3-1.5 (-1.8) mm long
               8 Culms markedly compressed, 3x wider than thick; distal leaf-sheath apex subtruncate, often with a tooth .6-1 mm long; spikelets narrowly lanceoloid, the scales 2.5-4 mm long, lanceolate and carinate; achenes 1.1-1.5 mm long, 0.8-1.2 mm wide
             7 Basal 2-3 scales sterile; spikelets 5-25 mm long, 3-7 mm wide; achene stramineous to dark brown; leaf sheath apex without tooth; [of the Mountains, rarely the Piedmont and scattered southwestward, widespread northward; e. and w. of MS river]
          6 Basal (proximal) scale of spikelet amplexicaulous (encircling the culm).
                 9 Achenes prominently reticulate-pitted or finely rugulose (at 10-20×); [of the outer Coastal Plain]
                 9 Achenes smooth to faintly reticulate; [of the Mountains, rarely Piedmont, or outer Coastal Plain].
                   10 Culms slender to filiform; scales obtuse, 30-40 per spikelet; scales 2-3.5 mm long; achenes 0.9-1.6 mm long; leaf sheath apex with tooth (0.1 mm long) sometimes present; [of basic soils, southward in the Mountains and rarely Piedmont, widespread northward]
                   10 Culms thicker, somewhat inflated; scales acute, 5-30 per spikelet; scales 3-4 mm long; achenes 1.3-1.8 mm long; leaf sheath apex without tooth; [of brackish habitats of the outer Coastal Plain, NC northward]
        5 Tufted or cespitose annuals without thick horizontal rhizomes; achenes persistent in spikelets, 0.3-1.2(-1.5) mm long; tubercles deltoid, or umbonate to subconic.
                     11 Mature achenes reddish-black to black; tubercles subconic to umbonate (with a knob-like protuberance); leaf sheath apex not bearing a tooth; [series Maculosae].
                       12 Spikes lance-ovoid to subcylindric; achene 0.3-0.5(-0.6) mm long, apex often constricted at junction with tubercle (achene with thin neck); bristles colorless or white
                       12 Spikes ovoid to subglobose; achene 0.7-1.0 mm long, apex rarely constricted at junction with tubercle (achene without thin neck); bristles red-brown (sometimes whitish)
                     11 Mature achenes white, brown, yellow, or occasionally greenish (never black); tubercles deltoid; leaf sheath apex present on some or all culms; [series Ovatae].
                          13 Tubercle < 0.5 mm wide, < 2/3 the width of the achene; achenes 0.75-1 mm long; spikelets ovoid.
                            14 Perianth bristles 2-4, or absent, if present then highly reduced or rudimentary (or rarely, equaling achene), never exceeding tubercle; tubercles 0.2-0.3 mm high; [fresh tidal river shores, rare; DE, NJ, and PA northward]
                          13 Tubercle > 0.5 mm wide, > 2/3 the width of the achene (often nearly as wide as achene); achenes 0.9-1.2 mm long; spikelets broadly ovoid to narrowly lanceoloid.
                                16 Spikelet narrowly lanceoloid, apex acute; scales ovate with acute apices; styles 2-fid only; tubercle 0.5-0.7 mm wide; culms typically 20-35 cm long; [west of MS river, disjunct and rare in TN]
                                16 Spikelet mostly broadly ovoid (sometimes ellipsoid/lanceoloid), apex usually rounded (sometimes acute); scales elliptic with rounded apices; tubercle 0.7-0.9 mm wide; styles 2-fid AND 3-fid; culms 3-50(-90) cm long; [widespread e. and w. of MS river]