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 0.3-0.6 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; [primarily west of MS river, with very scattered locations eastward]

............ 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).

............ ..8 Achenes prominently reticulate-pitted or finely rugulose (at 10-20×); [of the outer Coastal Plain]

............ ..8 Achenes smooth to faintly reticulate; [of the Mountains, rarely Piedmont, or outer Coastal Plain].

............ ....9 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]

............ ....9 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.

............ ......10 Mature achenes reddish-black to black; tubercles subconic to umbonate (with a knob-like protuberance); leaf sheath apex not bearing a tooth; [series Maculosae].

............ ........11 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

............ ........11 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)

............ ......10 Mature achenes white, brown, yellow, or occasionally greenish (never black); tubercles deltoid; leaf sheath apex present on some or all culms; [series Ovatae].

............ ..........12 Tubercle < 0.5 mm wide, < 2/3 the width of the achene; achenes 0.75-1 mm long; spikelets ovoid.

............ ............ 13 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 Perianth bristles 5-7, retrorsely barbed, exceeding tubercle; tubercles 0.3-0.5 mm high; [widespread, VA w. to MO northward]

............ ..........12 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.

............ ............ ..14 Bristles much shorter than the achene, rudimentary, or absent

............ ............ ..14 Bristles as long as or exceeding the tubercle, present.

............ ............ ....15 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]

............ ............ ....15 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]

1 Tubercle (0.9-) 1.2-1.7 mm long, noticeably larger than achene

1 Tubercle distinctly smaller than and not exceeding the achene size; at least the length, width, or both, smaller than achene dimensions (typically < 0.8 mm long).

..2 Achene apex conspicuously truncate and flattened; mature achenes black

..2 Achene apex not truncate; instead rounded towards the tubercle, the junction of the achene and tubercle with or without a tapered transition zone ("neck"); mature achenes variously colored (sometimes dark brown or chestnut brown, but never black).

....3 Tubercle confluent with achene (not clearly differentiated); thus, tubercle base and achene apex merged and with little to no demarcation.

......4 Achenes (0.75-) 0.9-1.2 mm long, stramineous to golden-yellow or pale brown colored; plants with tubers or terminating rhizomes noticeably J-shaped, 0.5-1 mm wide; [mostly coastal, brackish, or tidal habitats, rarely occurring within inland salt marshes, sect. Parvulae]

......4 Achenes 1.5-2.5 mm long, stramineous, medium brown, to gray-brown colored (greenish on immature achenes); plants tufted, tip-rooting, or rhizomatous (if rhizomatous, then with terminating bulbs, but not J-shaped tubers); [plants usually of inland fens, seepages, or other similar calcareous, or lime-influenced habitats; also in coastal, brackish marshes].

........5 Spikelets with 3-10 scales; achene apex with thin "neck" below confluent tubercle, plants without tip-rooting culms or proliferous spikelets (instead plants erect, with terminal bulbs usually present on creeping rhizomes); culms subterete to slightly compressed; culms up to 2x as wide as thick; [subgenus Zinserlingia]

........5 Spikelets with 20-40 scales; achene apex without "neck" below confluent tubercle, plants usually with some culms tip-rooting; culms compressed, 1.5-3x as wide as thick; [subgenus Eleocharis, ser. Rostellatae]

....3 Tubercle not confluent with achene (these structures distinguishable, with a distinct separation between).

..........6 Achene 1.2-1.7 (2.5) mm long; culms usually spirally twisted, acutely triangular or elliptic; scales spirally arranged; achenes coarsely honeycomb-reticulate

..........6 Achene 0.45-1.2 mm long; culms not spirally twisted, variously shaped; scales distichous, spiraled, or spirodistichous; achenes smooth to finely or coarsely honeycomb-reticulate.

............ 7 Some or most culms with the distal leaf sheath apex bearing a distinct tooth, the tooth (usually at least 0.2 mm long) sharpened to an apical point and much thinned from the obtuse or subtruncate (sometimes acute in E. tenuis) sheath below; distal leaf sheaths persistent (not splitting).

............ ..8 Achene surface smooth to finely reticulate (at 20-30x), not distinctly rugulose or honeycomb-reticulate; achenes 0.6-0.8 mm long; culms 20-55 cm long; [rare, s. TX].

............ ....9 Bristles 3-6, rudimentary to < 1/2 the achene length; achenes 0.6-0.65 mm long, compressed-trigonous; culms soft and spongy, without internal septae; spikelets narrowly lanceoloid to cylindric, 1-1.5 mm wide

............ ....9 Bristles 5-6, their length equaling the achene; achenes 0.6-0.8 mm long, occasionally some appearing biconvex; culms with internal septae (these only evident after sectioning the culm); spikelets lanceoloid, 2-2.5 mm wide

............ ..8 Achene surface honeycomb-reticulate or finely rugulose; achenes 0.6-1.2 mm long; culms 5-90 cm long; [collectively widespread].

............ ......10 Bristles present, 1-5 (E. fallax) or 5-6 (E. montevidensis), usually about as long as achene (rarely rudimentary); achenes compressed-trigonous with angles often obscured; [fresh to brackish habitats of the outer Coastal Plain].

............ ........11 Culms 40-70 cm tall; scales hyaline with red-brown to blackish brown central stripes; achenes prominently pitted like a honeycomb (prominently rugulose); tubercle 0.3-0.5 mm tall

............ ........11 Culms usually up to 37 cm tall (reportedly taller, but not verified; mostly < 25 cm tall in NC and SC); scales hyaline with orange-brown to dull orange central stripes (notably orangey on fresh specimens); achenes faintly or obscurely pitted (finely rugulose); tubercle 0.25-0.3 mm tall

............ ......10 Bristles absent, or if present only 1-3 (these usually falling at maturity); achenes keeled or prominently trigonous; [wet acidic or calcareous sites; throughout coastal plain or inland].

............ ..........12 Achenes with 3 prominent raised angles (keels); achene surface rugulose; bristles absent

............ ..........12 Achenes evidently trigonous, but lacking 3 prominent keels; achene surface finely to coarsely rugulose; bristles absent or present.

............ ............ 13 Achenes 0.7-1.2 mm long, persistent after scales fall; bristles absent or if present then to 1/2 the achene length; achene faces with 12-20 horizontal ridges (wavy rows) from apex to base of achene; culms usually 6-8 angled; [usually wet calcareous habitats; scattered PA southward, more common northward]

............ ............ 13 Achenes 0.6-0.9 mm long, not persistent (falling with or before scales); bristles absent or if present, 1-3, up to as long as achene length, and usually falling at maturity; achene faces with 6-12 ridges (or rows of depressed cells) from apex to base of achene; culms usually 4 (-5) angled; [widespread in e. US].

............ ............ ..14 Rhizomes (1.1-) 1.4-1.9 (-2.3) mm wide, appearing thick relative to short internode lengths of (0.9-) 1.3-2.6 (-4.4) mm, scales of rhizome (1.4-) 2.3-3.3 (-4.6) mm long; tubercles typically ¾ the width of achene, greatly depressed, rarely pyramidal; achenes 0.6-0.7 (-0.9) mm in length to base of tubercle by 0.5 (-0.7) mm wide, coarsely (to finely) rugose to cancellate (at 10× magnification); [intermittent from e. PA and NJ south to GA, west to e. NE, OK, and TX, where more common]

............ ............ ..14 Rhizomes 0.6-1.4 (-1.9) mm wide, appearing delicate or slender relative to long internode lengths of (2.6-) 3.5-7.7 (-10.0) mm, scales of rhizome (3.7-) 4.4-8.5 (-10.2) long; tubercles typically less than ¾ the width of achene, pyramidal to depressed; finely rugulose to finely cancellate (at 10× magnification).

............ ............ ....15 Culms sharply angled, usually deeply sulcate, to 0.8 mm wide; distal leaf sheaths usually with stout apical tooth 0.4-0.6(-0.9) mm; rhizomes slender, (0.8-) 0.9-1.4 (-1.9) mm wide, with longer internodes (3.2-) 4.6-7.7 (-10) mm, scales of rhizome (3.7-) 5.1-8.5 (-10.2) mm in length; tubercles depressed, rarely pyramidal (0.3-) 0.4-0.6 mm wide; achene elongate obovate to faintly spatulate, (0.7-) 0.9-1.1 mm long by 0.6-0.8 mm wide, obscurely to finely rugulose (at 10× magnification); [w. NC northeast to se. ME, disjunct to s. IL]

............ ............ ....15 Culms bluntly angled to smooth, seldom deeply sulcate, to 0.5 mm wide; distal leaf sheaths with or without apical tooth to 0.2 mm; rhizomes delicate to slender, 0.6-1.0 (-1.2) mm wide, with longer internodes (2.6-) 3.5-5.9 (-8.0), scales of rhizome (3.7-) 4.4-6.7 (-7.9) mm in length; tubercles pyramidal, rarely depressed (0.2-) 0.3-0.4 mm wide; achene obovate, rugulose to finely cancellate at 10×; [e. KY and w. NC northeast to NS]

............ 7 Distal leaf sheath apex of culms without a distinct, abrupt tooth; instead the sheath apex acute, blunt, or rounded; if sometimes with a subacute, linear blade (as in E. intermedia) then gradually widened at the base and otherwise with a papery or membranous texture; distal leaf sheaths often persistent, but sometimes membraneous and disintegrating.

............ ............ ......16 Achenes smooth, sometimes finely pitted (as in E. brittonii) or finely reticulate, i.e. with a network of veins or appearing lattice-like (as in E. baldwinii), but never bearing a distinctly wrinkled, honeycomb-reticulate, or otherwise textured surface.

............ ............ ........17 Proximal (bottom-most) scale of spikelet not amplexicaulous (only spanning 1/2 the width of culm); scales 10-100 per spikelet; culms elliptic, subterete, or terete (occasionally polygonal, but not conspicuously quadrangular or sulcate); plants without proliferous spikelets.

............ ............ ..........18 Bristles absent; plants cespitose annuals; achene length 0.5-0.6 mm, achene width 0.33-0.4 mm; culms 1-9 cm long, very soft; achenes pearly white to grayish; [primarily FL, rare further north; flatwoods and other moist, terrestrial sites]

............ ............ ..........18 Bristles present, 5-8 (usually 6); plants perennial with soft rhizomes; achene length 0.8-1 mm, achene width 0.7-0.8 mm; culms 10-40 cm long, soft to firm; achenes dark brown when mature; [MD to FL, w. to TX; brackish or highmarsh sites, usually coastal].

............ ............ ............ 19 Spikelets (2.3-) 2.4-3.2 (-3.7) mm wide; plants 15-24 (-28) cm tall, culm ± erect; achenes 0.65-0.8 mm wide; tubercles 0.25-0.3 (-0.35) mm wide; bristles rarely exceeding the tubercle, (0.8-) 1-1.1 (-1.2)× as long as achene-tubercle complex; [widespread from MD to FL, w. to TX]

............ ............ ............ 19 Spikelets 1.5-2.3 (-2.4) mm wide; plants 30-40 cm tall, culm lax; achenes 0.5-0.6 mm wide; tubercles 0.1-0.2 mm wide; bristles exceeding the tubercle, 1.2-1.7 (-2)× as long as achene-tubercle complex; [Camden Co., GA; perhaps to be found to be somewhat more widespread]

............ ............ ........17 Proximal (bottom-most) scale amplexicaulous (or nearly so); scales 2-28 per spikelet (13-76 in E. brittonii); culms typically quadrangular or sulcate (grooved), sometimes broadly elliptic; plants with or without proliferous spikelets.

............ ............ ............ ..20 Plants never with proliferous spikelets, rhizomes present (but plants still appearing cespitose or tufted); achenes white or brown, not spotted.

............ ............ ............ ....21 Bristles 6, equaling to far exceeding tubercle, red-brown; achenes trigonous with prominent angles; [FL]

............ ............ ............ ..20 Plants often with a few to many proliferous spikelets, without rhizomes; achenes white, brown, grey, green, olive, or reddish-brown, spotted or not.

............ ............ ............ ......22 Scales 2-ranked, obviously distichous; scales fewer, typically 2-4 (-9); bristles 6

............ ............ ............ ......22 Scales spirally imbricate or spirodistichous (i.e. appearing superficially spiraled as in E. minima); scales >10 per spikelet (occasionally as few as 4 in E. minima); bristles present or absent.

............ ............ ............ ........23 Spikelets with proximal scale deciduous or sometimes persistent on some spikelets, proximal scale appearing similar to other scales (when still present); achenes greenish to pale or reddish brown, usually broadest near the middle; perianth bristles present, slightly shorter than achene to exceeding tubercle; culms (1-) 3-7 (-13) cm long, usually flexuous and recurved; tubercle 0.15-3 mm long, broad, covering most of achene summit; [GA and FL w. to TX]

............ ............ ............ ........23 Spikelets with proximal scale persistent, clearly different from floral scales, usually longer and often resembling involucral bract, often with an excurrent midrib; achenes white or pale gray, broadest above the middle; perianth bristles present or absent, rudimentary to equaling achene; culms 2-40 cm long, ascending or arching; tubercle 0.05-0.2 mm long, shortly pyramidal or birettaform, perched at achene summit and not covering most of it; [collectively widespread].

............ ............ ............ ..........24 Proximal scale with rounded apex, the scale elliptic or lanceolate, the tip appressed; scale apices rounded throughout spikelet; perianth bristles shorter than achene or absent; tubercle birettaform (with 3-4 small peaks; resembling a biretta); culms 7-37 cm long

............ ............ ............ ..........24 Proximal scale with subacute to acute apex, the scale ovate or lanceolate, the tip free; scale apices attenuate to acute throughout spikelet; perianth bristles vestigial to equaling achene or sometimes absent; tubercles pyramidal, semicircular, or birettaform; culms 2-40 cm long.

............ ............ ............ ............ 25 Perianth bristles 0.6-1.0 mm long (shorter than to equaling the achene); proximal scale of the spikelets 0.8-1.0 mm wide

............ ............ ............ ............ 25 Perianth bristles 0.2-0.4 mm long (shorter than the achene); proximal scale of the spikelets 0.4-0.5 mm wide

............ ............ ......16 Achenes finely rugulose (with a wrinkled texture) or honeycomb-reticulate, bearing some texture.

............ ............ ............ ............ ..26 Culms distinctly compressed (sometimes subterete-compressed in E. compressa var. acutisquamata); at least some scales bifid or shallowly cut; [habitat often calcareous or limestone-derived].

............ ............ ............ ............ ....27 Plants densely cespitose (rhizomes present, but concealed by persistent living or dead culm bases); spikelet scales primarily bifid throughout.

............ ............ ............ ............ ......28 Culm width 0.7-2.3 mm; proximal-most scale of spikelet clasping 2/3-3/4 of culm; flowering and fruiting mostly May-June; [KY and w. VA south through TN to nw. GA and n. AL]

............ ............ ............ ............ ......28 Culm width 0.2-0.5 (-0.7) mm; proximal-most scale of spikelet amplexicaulous; flowering and fruiting mostly March-May (-July); [endemic to OK and TX]

............ ............ ............ ............ ....27 Plants perennial, mat-forming (rhizomes not hidden by culm bases); spikelets a mix of entire and bifid scales (the proximal-most scale entire, remaining proximal 1/2 of scales bifid or shallowly cut, and distal scales often entire).

............ ............ ............ ............ ........29 Culms subterete to slightly compressed, not more than 2 times as wide as thick, (0.2-) 0.5-1 mm wide; [IN, MO, OK, TX, westward]

............ ............ ............ ............ ........29 Culms bi-laterally compressed, 2-5 times as wide as thick, 0.5-1.8 mm wide; [widespread east of Mississippi River, also north of LA and OK]

............ ............ ............ ............ ..26 Culms not compressed; instead terete, subterete, elliptic, sulcate (grooved) or with 4-many ridges; if culms ridged, the ridges sometimes sharp and often most evident when culms have dried; apex of scales entire, not bifid (except for E. occulta); [habitat calcareous or acidic].

............ ............ ............ ............ ..........30 Spikelets with 2-6 scales; achene apex broad and flattened; tubercle base trilobed, the lobes decurrent along achene angles; [rare, possible ballast waif near Mobile, AL and potentially other Gulf coastal sites]

............ ............ ............ ............ ..........30 Spikelets with 5-60 scales; achene apex not flattened, instead constricted gradually or abruptly towards apex at junction with tubercle; tubercle not trilobed; [widespread]

............ ............ ............ ............ ............ 31 Culms bluntly, smoothly, or deeply sulcate, usually 4 (-5) angled with evident ridges or angles; achenes coarsely honeycomb reticulate

............ ............ ............ ............ ............ 31 Culms not sharply angled; instead terete, subterete, broadly elliptic, or subterete-compressed; achenes papillose, or finely to coarsely honeycomb reticulate.

............ ............ ............ ............ ............ ..32 Scales of spikelet bifid, 20-50 scales per spikelet; plants densely cespitose and with horizontal rhizomes present (although these obscured by persistent leaf bases); [endemic to OK and TX]

............ ............ ............ ............ ............ ..32 Scales of spikelet acute or obtuse, not bifid; 5-35 scales per spikelet; plants cespitose or with proliferous spikelets, but lacking horizontal rhizomes; [collectively widespread]

............ ............ ............ ............ ............ ....33 Achenes 0.6-0.8 mm long, gray or greenish colored, trigonous with prominent angles; plants often bearing some proliferous spikelets; tubercle > 1/3 the length of the achene; [VA s. to FL, w. to TX]

............ ............ ............ ............ ............ ....33 Achenes 0.9-1.1 mm long, golden yellow to golden brown colored, compressed-trigonous to nearly terete; plants without proliferous spikelets; tubercles typically 1/3 or less than the length of the achene; [TN and NC northward].

............ ............ ............ ............ ............ ......34 Plants rhizomatous perennials; achene compressed-trigonous, obovoid to obpyriform; tubercle pyramidal, the width equaling the length; [of coastal fresh to brackish ponds, lakeshores, marshes, and similar habitats; NS s. to NJ, disjunct in e. NC]

............ ............ ............ ............ ............ ......34 Plants annual, cespitose (with inconspicuous rhizomes); achene nearly terete, narrowly obpyriform; tubercle slender-conic with narrow base; [of basic soils inland, common northeast, scattered southward in WV, VA, and TN] .