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 absent, or if present, 1-4, rudimentary to shorter than achene length, colorless to white; achenes typically biconvex, but rarely trigonous; [GA and FL w. to MS]

                                           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]