1 Plants spreading primarily via proliferous spikelets and tip-rooting culms OR growing as submersed or floating aquatics with only vegetative culms present (these either simple and flaccid or proliferous); plants sometimes with a few fertile culms that bear spikelets but otherwise primarily vegetative; culms usually sprawling; tip-rooting culms dark green and firm, OR wiry, weak and light green colored; plants growing submersed in water or sprawling on moist exposed soil in areas with seasonal drawdown

1 Plants primarily with fertile spikelets born at the apex of culms, occasionally with a few proliferous spikelets, but rarely spreading primarily via vegetative means; culms erect, decumbent, or reclining, robust or diminutive; plants cespitose OR rhizomatous and mat-forming; plants growing as terrestrial or emergent wetland plants.

  2 Culms transversely nodose-septate, these cross partitions complete and evident through the outside of culms (fresh culms appear ribbed); achenes biconvex; [subgenus Limnochloa, in part]

  2 Culms not transversely nodose-septate OR if so, septae incomplete, internal, and not evident on the outside of fresh culms (only evident upon sectioning culm); achenes biconvex, terete, trigonous, or compressed-trigonous.

    3 Spikelets distinctly long and cylindric (> 4× as long as wide); the width of the spikelets the same as the culm width, thus not conspicuously expanded from the culms below; the base of the spikelets narrowly cuneate; achenes biconvex; [subgenus Limnochloa , in part]

    3 Spikelets typically ovoid, but also terete, lanceoloid, or ellipsoid and rarely cylindric (e.g. E. palustris), < 4× as long as wide; spikelets distinctly wider than the culms, thus obviously differentiated and expanded from the culms below; the base of the spikelets broadly cuneate, rounded, or truncate; achenes biconvex, terete, trigonous, or compressed-trigonous.

      4 Achenes bearing several (6-13) longitudinal ribs with very narrow horizontally elongate cells between, these ribs conspicuously raised from the achene surface; achenes diminutive, < 1.1 mm long; [subgenus Scirpidium]

      4 Achenes not bearing 6 or more longitudinal ribs; if bearing indistinct ribs, then achenes do not have thin horizontal intervening cells (as in E. tortilis and E. tuberculosa), or if bearing 3 distinct keels, these only along the margins of each achene face (as in E. tricostata); achenes diminutive to large (0.5-2.5 mm long), their surfaces smooth, finely reticulate or veined, rugulose, or honeycomb-reticulate.

        5 Achenes primarily lenticular or biconvex (therefore achene with only 2 prominent faces); styles mostly 2-branched (occasionally with some 3-branched).

          6 Plants without whorled vegetative proliferations; emergent in a variety of wetlands; spikelets with a few to many flowers or scales (usually 8 or more); achenes terminated by a tubercle; [subgenus Eleocharis, in part].

        5 Achenes primarily trigonous (sometimes compressed trigonous or plano-trigonous), therefore with 3 prominent to obscured faces OR achenes nearly terete; achenes bearing more than only 2 obvious sides, these marked with obvious keels or rounded edges, OR almost entirely rounded and thus without any prominent faces; styles mostly 3-branched (occasionally with some 2-branched); [subgenus Eleocharis, in part, except for E. quinqueflora].

1 Plants producing only vegetative culms, no reproductive culms present.

  2 Culms usually firm or hard, 0.35-3 mm wide, compressed; plants tip-rooting in terrestrial wetland habitats.

    3 Culms 0.35-2 mm wide; bearing up to 8 subacute ribs; distal leaf sheath not bearing an apical tooth [calcareous brackish or tidal habitats, inland calcareous fens, other similar limestone-influenced wetlands; ME, ON, south to FL, TX, further westward]

    3 Culms 0.5-1.3 mm wide; usually with 10 blunt ribs, finely ridged and minutely granular (at 20x); distal leaf sheath nearly always bearing an apical tooth up to 2 mm long; [freshwater habitats, coastal plain ponds, often acidic; MA w. to MI, south to TX and FL]

  2 Culms wiry, soft, 0.1-0.7 mm wide, variously shaped but not conspicuously compressed; plants growing submersed or floating in aquatic habitats (e.g. creeks, ponds, rivers).

      4 Plants with rhizomes (0.5-2 mm thick); with submersed flaccid culms internally spongy bearing incomplete transverse septae (aquatic forms).

        5 Tubers absent; culms emerging from jointed elongate stolons; [Sinkhole ponds, depression ponds, sawgrass sloughs, lakeshores, creeks, canals, ditches; NC to FL, w. to TX]

        5 Tubers sometimes present; plants with rhizomes but typically growing more tufted; [Sinkhole ponds, depression ponds, blackwater impoundments, natural lakes, millponds, springs; typically fresh-water habitats; Ont. and Que. south to MS and FL]

      4 Plants without pronounced rhizomes (sometimes with short caudexlike rhizomes in E. vivipara), submersed or flaccid culms lacking transverse septae.

          6 Culms producing secondary or tertiary proliferations (proliferous spikelets branching more than once per culm).

             7 Base of whorl gradually widened from culm, vase-shaped, not forming a distinct shoulder; whorl divisions fewer per whorl (commonly 15 or less); whorl divisions usually 0.3 mm or more wide (0.5 mm or more, but the finest secondary or tertiary divisions as slender as 0.15 mm); surface texture of divisions not beaded (under dissecting microscope); plants appearing less "fan-like" towards terminal whorls

          6 Culms producing a single proliferous spikelet (not proliferating more than once per culm).

               8 Upper portion of sheath thin and scarious, the edge not differently colored (sometimes with a few red-brown spots or streaks, but not with concentrated red dots at the tips); sheath tip 1-2 mm long; plants usually filiform and capillary; without rhizomes

               8 Upper portion of sheath firm, the edge closely red-dotted; sheath tip < 1 mm long; plants soft or firm (emergent plants typically more robust); with thin caudex-like rhizomes

1 Plants with a few reproductive culms present; plants thus a mix of predominantly vegetative culms (bearing proliferous spikelets) and a few spikelet-bearing culms.

                 9 Culms wider, 0.35-2 mm in diameter, typically strong or firm, usually darker green colored with erect and arching culms, not spotted.

                   10 Leaf sheath summit with narrow tooth (up to 1 mm long); achene blackened, apex widened and truncate; [widespread, primarily in Coastal Plain, disjunct in Ridge and Valley province of VA]

                   10 Leaf sheath summit truncate, sometimes with callous swelling; achene green to medium or dark brown, apex rounded, not widened and truncate; [widespread northward within calcareous fens and brackish wetlands, scattered southward in brackish habitats]

                 9 Culms thinner, 0.1-0.4 (-0.6) in diameter, soft and wiry, often arching and light green colored, sometimes spotted or red-brown streaked.

                     11 Culms producing 2 or 3 proliferous whorls; plants usually growing aquatically or submersed under water in ponds, lakes, or depressions.

                       12 Spikelets with 5-25 scales, spiraled; achenes trigonous with prominent angles, with a pronounced tubercle (plants often with some reproductive culms)

                     11 Culms only producing 1 proliferous whorl; plants growing submersed in water or emergent in drawdown zones of ponds and other aquatic or wetland habitats.

                          13 Achenes finely to coarsely honeycomb-reticulate or with an otherwise reticulate or porose surface.

                            14 Scales 2-6 per spikelet, arranged distichously; tubercle trilobed and decurrent on achene sides; [waif; Mobile, AL]

                            14 Scales 5-25 per spikelet, spiraled; tubercle trigonous, not decurrent on achene sides [widespread in southeastern Coastal Plain]

                          13 Achenes smooth to finely reticulate, but lacking a defined porose or textured surface.

                              15 Achenes often spotted, gray or greenish to red-brown; spikelets distichous or spirodistichous; sheath apex obtuse, acute, or narrowly acute; bristles clearly or sparsely retrorsely spinulose

                                16 Sheath apex obtuse or acute; spikelets distichous at maturity; bristles 3-7

                                16 Sheath apex narrowly acute, membranous, usually with torn edge; spikelets spirodistichous at maturity (appearing superficially spiraled); bristles 6

                              15 Achenes not spotted (or rarely spotted), usually white or light grey colored; spikelets spiraled; sheath apex narrowly acute; bristles not evidently spinulose

                                  17 Scale apices rounded throughout, typically more uniform white-colored; proximal scale tip appressed to basal scales; tubercle birettaform; bristles to 0.3 mm long (distinctly shorter than achene) or absent

                                  17 Scale apices subacute to acute throughout (sometimes a few obscurely rounded), typically with red-tinging on the scale margins; proximal scale free (i.e. not tightly appressed to basal scales); tubercle pyramidal, semicircular, or birettaform; bristles 0.2-1.0 mm long (shorter than or equaling achene, rarely absent)

                                    18 Perianth bristles 0.6-1 mm long, shorter than to equaling achene; proximal scale of spikelets 0.8-1 mm wide

                                    18 Perianth bristles 0.2-0.4 mm long, shorter than achene; proximal scale of spikelets 0.4-0.5 mm wide