Plants perennial or annual, sometimes with spikelets proliferating or some culms arching or decumbent and rooting at tips. Rhizomes present or absent, without bulb; tubers rarely present (in 8a3. Eleocharis sect. Parvulae), terminating rhizomes or among culm bases. Culms usually spongy with incomplete transverse septa, seldom hollow with complete transverse septa in 8a1a. E. sect. Eleocharis ser. Eleocharis. Spikelets mostly ovoid, seldom cylindric or narrowly ellipsoid, usually much narrower than their culms; proximal internodes of rachilla as long and as thick as middle and distal internodes; proximal scale usually empty; floral scales with 1 vein, or rarely to 10 longitudinal parallel veins; basal spikelets rarely present in 8a1d. E. sect. Eleocharis ser. Tenuissimae. Achenes smooth, rugulose, or reticulate, or with longitudinal rows of enlarged cells, without fine horizontal ridges between more prominent longitudinal ridges, rarely distally narrowed into distinct beak. Tubercles clearly distinct from achene apex, or if merging with achene apex in color, texture, and form, then achenes mostly with distinct distal beak and many culms usually arching or decumbent and rooting at tips (8a1c. E. sect. Eleocharis ser. Rostellatae).
Contents
Distribution
Worldwide.
Discussion
Species ca. 160 (49 in the flora).
Selected References
None.
Lower Taxa
None.
Key
Key to the species of Eleocharis subg. Eleocharis
| 1 | Styles 2-fid, sometimes to 1/3 3-fid; achenes biconvex or sometimes to 1/3 trigonous, smooth or finely rugulose at 10–20X; plants never stoloniferous or proliferating from spikelets. | > 2 |
| 1 | Styles 3-fid, sometimes to 2/3 2-fid; achenes trigonous, or subcircular in cross section, or sometimes mostly biconvex, smooth to prominently variously sculptured at 10X; plants sometimes stoloniferous or proliferating from spikelets. | > 22 |
| 2 | Distal leaf sheaths often disintegrating, delicately membranous, usually prominently inflated and conspicuously wrinkled; culms 0.1–0.6 mm wide; creeping rhizomes present (often inconspicuous). | > 3 |
| 2 | Distal leaf sheaths evident, rarely disintegrating, firmly membranous to papery, not prominently inflated or conspicuously wrinkled; culms 0.3–5 mm wide; creeping rhizomes present or absent. | > 4 |
| 3 | Culms 0.3–0.6 mm wide; distal leaf sheaths distally inflated, conspicuously wrinkled, apex blunt; achenes green to dark brown; locally common, widespread. | Eleocharis flavescens |
| 3 | Culms 0.1–0.3 mm wide; distal leaf sheaths often not evident, closely sheathing, not wrinkled, apex acute; achenes whitish to pale brown; very uncommon, se coastal plain. | Eleocharis bicolor |
| 4 | Plants annual (rarely perennial?), without creeping rhizomes; anthers 0.2–1 mm; achenes green, stramineous, pale brown, dark brown, or black; distal leaf sheath apex narrowly acute to acuminate. | > 5 |
| 4 | Plants perennial, with creeping rhizomes; anthers 1–2.5 mm; achenes yellow to dark brown or sometimes green; distal leaf sheath apex truncate to subacute. | > 12 |
| 5 | Tubercles not strongly dorsiventrally compressed, cross section shape similar to shape of achene, not sessile on achene; achenes brown ripening to black; distal leaf sheath apex not toothed. | > 6 |
| 5 | Tubercles strongly compressed dorsiventrally, cross section shape proportionally much thinner than shape of achene, sessile on achene; achenes stramineous to dark brown; distal leaf sheath apex often toothed. | > 7 |
| 6 | Achenes 0.5–1.1 × 0.3–0.7 mm, apex rarely constricted proximal to tubercle; perianth bristles red-brown, rarely whitish; spikelets with scales membranous to often cartilaginous; culms 3–45 cm. | Eleocharis geniculata |
| 6 | Achenes 0.3–0.5 × 0.3–0.4 mm, apex often constricted proximal to tubercle; perianth bristles colorless or white; spikelets with scales membranous; culms 2–12(–19) cm. | Eleocharis atropurpurea |
| 7 | Tubercles not more than 1/4 as high as achene (rarely to 2/5 as high as achene in E. engelmannii var. robusta, 1/10–1/2 as high as wide); perianth bristles shorter than achene to ± equaling tubercle, or often absent. | > 8 |
| 7 | Tubercles 1/4 or more as high as achene, 1/3 to as high as wide; perianth bristles equaling to usually markedly exceeding tubercle, rarely shorter or absent. | > 9 |
| 8 | Tubercles 0.1–0.2 × 0.25–0.45 mm, 1/3–1/2 as high as wide; perianth bristles absent; spikelets ovoid, scales acute; very local in Northeast. | Eleocharis diandra |
| 8 | Tubercles (0.1–)0.2–0.3(–0.4) × 0.6–0.9(–1) mm, 1/10–2/5 as high as wide; perianth bristles present or absent; spikelets lanceoloid to subcylindric or ovoid, scales subacute to narrowly rounded; widespread. | Eleocharis engelmannii |
| 9 | Tubercles 0.3–0.5 mm wide; spikelets ovoid. | > 10 |
| 9 | Tubercles 0.5–0.8 mm wide; spikelets broadly ovoid to lanceoloid (or ellipsoid or subcylindric). | > 11 |
| 10 | Perianth bristles (5–)6–7, exceeding tubercle, spinulose, very rarely absent; tubercles 0.3–0.5 mm high; widespread. | Eleocharis ovata |
| 10 | Perianth bristles 2–4, rudimentary to rarely equaling achene, smooth, or often absent; tubercles 0.2–0.3 mm high; ne fresh tidal river shores. | Eleocharis aestuum |
| 11 | Spikelets lanceoloid (to broadly ovoid), apex acute; spikelet scales ovate with apices acute (or sometimes narrowly rounded in distal part of spikelet); perianth bristles equaling or slightly exceeding tubercle; styles all 2-fid; stamens 2; sc United States, disjunct in California. | Eleocharis lanceolata |
| 11 | Spikelets ovoid (to ellipsoid or subcylindric), apex rounded (to acute); spikelet scales elliptic with apices broadly rounded; perianth bristles slightly to usually greatly exceeding tubercle; styles 3-fid and 2-fid (rarely all 2-fid or all 3-fid?); stamens 3 (or 2); widespread. | Eleocharis obtusa |
| 12 | All or some culms with distal leaf sheath apex with distinct, abrupt tooth. | > 13 |
| 12 | All culms with distal leaf apex without distinct, abrupt tooth. | > 16 |
| 13 | Culms hollow with complete transverse septa usually evident without sectioning culm; spikelets with 100–500+ scales, 15–40 per mm of rachilla; rhizomes mostly hidden by culms and roots, 3 mm thick. | Eleocharis montana |
| 13 | Culms spongy, the transverse septa incomplete; spikelets with 5–200 scales, 3–10 per mm of rachilla; rhizomes evident, not hidden by culms and roots, 1–2 mm thick. | > 14 |
| 14 | Proximal scale of spikelets clasping (2/3–)3/4 (rarely all) of culm; subproximal scale of some (rarely all) spikelets without flower (empty); culms usually distinctly compressed; achenes smooth at 30X or finely rugulose at 10–20X; tubercles as high as wide or higher. | Eleocharis macrostachya |
| 14 | Proximal scale of spikelets clasping all of culm (amplexicaulous); subproximal scale of all spikelets with flower; culms terete; achenes finely rugulose at 10X; tubercles sometimes lower than wide. | > 15 |
| 15 | Tubercles 0.15–0.3(–0.5) mm, mostly much lower than wide; achenes finely rugulose at 10X; Atlantic and Gulf coastal plains. | Eleocharis ambigens |
| 15 | Tubercles 0.35–0.65 mm, mostly at least as high as wide; achenes smooth at 30X or finely rugulose at 10–30X; widespread. | Eleocharis erythropoda |
| 16 | Proximal scale of spikelets clasping 2/3(–3/4) of culm; all spikelets with empty subproximal scale. | > 17 |
| 16 | Proximal scale of spikelets clasping 3/4+ of culm; subproximal scale with flower or empty. | > 18 |
| 17 | Perianth bristles (4–)5–6(–8), exceeding tubercle; achene apex without distinct neck, tubercles sessile on achenes; mostly boreal. | Eleocharis mamillata |
| 17 | Perianth bristles 0–4(–5), rarely exceeding tubercle; achene apex with or with out distinct neck, tubercles often not sessile on achenes; widespread. | Eleocharis palustris |
| 18 | Subproximal scale of some spikelets of plant empty; proximal scale of some or all spikelets usually clasping less than all of culm. | Eleocharis macrostachya |
| 18 | Subproximal scale of all spikelets of plant with flower; proximal scale of all spikelets clasping all of culm (amplexicaulous). | > 19 |
| 19 | Tubercles more than 2/3 as high and wide as achene, usually with vertical rows of prominent depressions when fully mature; floral scales 2–3 mm wide, 1–2 per mm of rachilla; boreal and subarctic coasts. | Eleocharis kamtschatica |
| 19 | Tubercles less than 2/3 as high and wide as achene, usually without vertical rows of depressions; floral scales 1.5–2(–2.5) mm wide, (2–)3–5 per mm of rachilla; ranges various. | > 20 |
| 20 | Tubercles mostly wider than high, 0.15–0.3(–0.5) mm; achenes finely rugulose at 10X; Atlantic and Gulf coastal plains. | Eleocharis ambigens |
| 20 | Tubercles mostly at least as high as wide, 0.35–0.8 mm; achenes smooth at 30X or finely rugulose at 10–30X; widespread. | > 21 |
| 21 | Floral scales in middle of spikelet not more than 1.8 mm wide, 4– 5 per mm of rachilla. | Eleocharis erythropoda |
| 21 | Floral scales in middle of spikelet 1.8–2.5 mm wide, 2–4 per mm of rachilla. | Eleocharis uniglumis |
| 22 | Achenes biconvex or sometimes less than 1/3 of achenes compressed trigonous, smooth; tubercles strongly compressed dorsiventrally, in cross section much thinner than achene; plants tufted annuals; spikelets not proliferous. | > 23 |
| 22 | Achenes trigonous or subterete or to 2/3 of achenes biconvex, smooth to variously sculptured; tubercles not strongly compressed dorsiventrally, in cross section similar in shape to achene; plants rhizomatous or tufted perennials or tufted annuals or stoloniferous; spikelets sometimes proliferous. | > 24 |
| 23 | Tubercles not more than 1/4 as high as achene, 0.1–0.3 mm (rarely 2/5 as high as achene and 0.4 mm high in E. engelmannii var. robusta); perianth bristles often absent, rudimentary to slightly exceeding tubercle. | Eleocharis engelmannii |
| 23 | Tubercles 1/3–1/2 as high as achene, 0.35–0.5 mm; perianth bristles present (very rarely absent), slightly to usually greatly exceeding tubercle. | Eleocharis obtusa |
| 24 | Some or all culms with distal leaf sheath apex with distinct, abrupt tooth; distal leaf sheaths persistent. | > 25 |
| 24 | Culms with distal leaf sheath apex without distinct, abrupt tooth; distal leaf sheaths persistent or disintegrating. | > 37 |
| 25 | Culms hollow, complete transverse septa not evident externally; achenes smooth or very finely reticulate at 20–30X; s Texas. | Eleocharis ravenelii |
| 25 | Culms spongy, transverse septa incomplete; achenes smooth to prominently sculptured; ranges various. | > 26 |
| 26 | Spikelets with some or all scales except the proximal emarginate to 2-fid. | > 27 |
| 26 | Spikelets with all scales entire. | > 29 |
| 27 | Some or all floral scales with apex acute to acuminate, 2-fid to shallowly cut, with translucent apex in middle part of spikelet 0.6–1.5 mm and mostly longer than wide; culms subterete, to 5 times wider than thick, to 1.8 mm wide; rhizomes 2–3 mm thick, longer internodes to 2 mm; achenes rugulose at 10–30X. | Eleocharis compressa |
| 27 | Some or all floral scales with apex rounded, obtuse, or acute, shallowly notched to deeply cut, with translucent apex in middle part of spikelets 0.2–0.7 mm and at least as wide as long; culms terete or subterete, to 2 (rarely 3) times wider than thick, to 0.8 mm wide; rhizomes 0.5–2.5 mm thick, longer internodes 2–10 mm; achenes rugulose or cancellate at 10X. | > 28 |
| 28 | Culms 4–5(–6)-angled or terete, not compressed; achenes falling with or before scales, with 6–12 depressions in each vertical row, yellow, brown, or green; floral scales shallowly notched or some entire. | Eleocharis tenuis |
| 28 | Culms (4–)5–10-angled or sometimes terete or often compressed; achenes persistent after scales fall, with 12–20 horizontal ridges in each vertical series, yellow, orange, or medium brown, rarely greenish; floral scales shallowly to deeply notched or deeply cut or some entire. | Eleocharis elliptica |
| 29 | Plants densely tufted from short, caudexlike rhizomes concealed by crowded culms; achenes dark brown to black, seldom yellow-brown, smooth, subdeltoid in outline to obpyriform; some culms often arching or decumbent and with tips rooting. | Eleocharis melanocarpa |
| 29 | Plants mat-forming, with long rhizomes that are not concealed by culms; achenes yellow, orange, brown, or green when mature, smooth to rugulose or alveolate (cancellate), ellipsoid, ovoid or obpyriform; culms never with tips rooting. | > 30 |
| 30 | Scales in proximal 1/2 of spikelet broadly rounded, usually many wrinkled and recurved; achenes obscurely to clearly rugulose and/or minutely cancellate at 10–30X. | > 31 |
| 30 | Scales in proximal 1/2 of spikelet rounded to acute, usually not wrinkled or recurved; achenes smooth to clearly sculptured. | > 32 |
| 31 | Rhizomes with scales fibrous, longer internodes 1.5–3 mm; achene angles prominent (keeled). | Eleocharis tricostata |
| 31 | Rhizomes with scales not fibrous, longer internodes 1–2 cm; achene angles not prominent. | Eleocharis montevidensis |
| 32 | Spikelets narrowly lanceoloid, narrowly ovoid, or narrowly cylindric; achenes smooth or minutely cancellate at 20–30X. | > 33 |
| 32 | Spikelets ovoid; achenes rugulose or cancellate at 10X. | > 34 |
| 33 | Achenes ellipsoid, 0.6–0.65 × 0.4–0.45 mm, smooth at 40X, angles prominent (keeled); floral scales 1.5–2 mm; spikelets 1.5 mm thick; s Texas, very uncommon. | Eleocharis cylindrica |
| 33 | Achenes obovoid to obpyriform, 0.8–1.4 mm × 0.5–0.7 mm, smooth, or cancellate at 20–30X, angles evident to obscure, not prominent; floral scales 2–3 mm; spikelets 1.5–3 mm thick; Southwest, locally common. | Eleocharis parishii |
| 34 | Achenes more than 0.95–1.25 mm wide, finely rugulose at 10–20X, not persistent after scales fall; rhizomes with longer internodes 5–10(–20) mm; culms terete, never compressed; uncommon, ne coast. | Eleocharis fallax |
| 34 | Achenes 0.45–0.9 mm wide, finely to coarsely rugulose and often cancellate at 10–20X, sometimes persistent after scales fall; rhizomes with longer internodes from very short to 10 mm; culms terete or angled, often clearly compressed; locally common, widespread. | > 35 |
| 35 | Rhizomes with longer internodes to 2 mm, 2–3 mm thick; achenes falling with scales or some persistent; culms seldom compressed, to 1.8 mm wide. | Eleocharis compressa |
| 35 | Rhizomes with longer internodes 2–10 mm, 0.5–2.5 mm thick; achenes falling with scales or persistent after scales fall; culms angled or terete, seldom compressed, to 0.8 mm wide. | > 36 |
| 36 | Culms with 4–5(–6) angles or sometimes terete, not compressed; achenes falling with or before scales, yellow to dark brown or green, with 6–12 depressions in each vertical series. | Eleocharis tenuis |
| 36 | Culms with (4–)5–10 ridges or angles, or terete or sometimes compressed; achenes yellow, orange, or medium brown, with 12–20 depressions in each vertical series. | Eleocharis elliptica |
| 37 | Spikelets with some or all scales shallowly notched to 2-fid; distal sheaths persistent. | > 38 |
| 37 | Spikelets with all scales entire; distal sheaths persistent or disintegrating. | > 42 |
| 38 | Spikelets with all scales 2-fid; rhizomes not evident, concealed by persistent culm bases, 3–5 mm thick, internodes very short; styles all 3-fid; achenes all nearly equilaterally obscurely trigonous or subcircular in cross section, obscurely rugulose at 10–30X. | > 39 |
| 38 | Spikelets with proximal scale entire, and some floral scales also often entire; rhizomes evident, not concealed by culm bases, 0.4–3 mm thick, longer internodes very short to 10 mm; some styles often 2-fid; some achenes often compressed trigonous or biconvex, clearly rugulose and/or cancellate at 10X. | > 40 |
| 39 | Culms subterete to slightly compressed, less than 2 times wider than thick, 0.2– 0.7 mm wide; Texas and Oklahoma. | Eleocharis occulta |
| 39 | Culms greatly compressed, 4–10 times wider than thick, 0.7–2.3 mm wide; Tennessee and adjacent states. | Eleocharis bifida |
| 40 | Floral scales with apex acute to acuminate, all 2-fid or some in same spikelet entire, in middle part of spikelet with colorless, hyaline apex 0.6–1.5 mm and mostly longer than wide; culms subterete to greatly compressed, to 1.8 mm wide; rhizomes 2–3 mm thick, longer internodes to 2 mm. | Eleocharis compressa |
| 40 | Floral scales with apex rounded to obtuse, rarely acute, emarginate to 2-fid or some in same spikelet entire, in middle part of spikelet with colorless, hyaline apex 0.2–0.7 mm and at least as wide as long; culms mostly not compressed, sometimes to 2 or rarely 3 times as wide as thick, to 0.8 mm wide; rhizomes 0.4–2.5 mm thick, longer internodes 2–10 mm. | > 41 |
| 41 | Culms 4–5(–6)-angled or sometimes terete, not compressed; achenes falling with or before scales, with 6–12(–14) depressions in each vertical series, yellow, brown, or green. | Eleocharis tenuis |
| 41 | Culms (4–)5–10-angled, or terete, or compressed; achenes persistent after scales fall, with 12–20 ridges in each vertical series, dark yellow, orange, or brown. | Eleocharis elliptica |
| 42 | Distal leaf sheath apices persistent, membranous to papery, subtruncate to obtuse, seldom acute; plants perennial, with creeping rhizomes or short, mostly ascending, caudexlike rhizomes. | > 43 |
| 42 | Distal leaf sheath apices either persistent, membranous to papery, acute to lanceolate, or disintegrating; plants annuals or perennials, with or without creeping or caudexlike rhizomes. | > 56 |
| 43 | Plants densely tufted from short, caudexlike rhizomes mostly hidden by culms, the internodes and scales usually not evident; creeping rhizomes absent. | > 44 |
| 43 | Plants mat-forming or sometimes densely tufted, with creeping rhizomes, internodes and scales evident (often hidden by culms and roots in E. decumbens). | > 49 |
| 44 | Tubercles merging with achene apex in color, texture, and form, often rudimentary or absent; achenes smooth to rugulose at 10X or finely reticulate at 20–30X, usually with distinct distal beak, often paler than rest of achene; culms clearly compressed, to 2 mm wide, firm to hard, some culms (stolons) usually arching or decumbent with tips rooting. | Eleocharis rostellata |
| 44 | Tubercles clearly distinct from achene apex in color, texture, and/or form, usually well developed; achenes smooth to rugulose, or finely or coarsely cancellate, without distinct beak; culms clearly compressed or not, sometimes arching or decumbent and culm tips rooting or spikelets proliferating. | > 45 |
| 45 | Achenes with each face with 8–10 longitudinal rows of large depressions, 0.9–1.7 mm; spikelets with scales papery, seldom membranous; distal leaf sheaths persistent; spikelets not proliferating, with scales papery to cartilaginous, seldom membranous; culm tips not rooting; Atlantic and Gulf coastal plains. | > 46 |
| 45 | Achenes smooth or obscurely to clearly sculptured at 10–30X, without longitudinal rows of large depressions, or sometimes each face with more than 20 longitudinal rows of small depressions; distal leaf sheaths sometimes disintegrating; spikelets sometimes proliferating, with scales membranous, seldom papery; culm tips often rooting; ranges various. | > 47 |
| 46 | Tubercles distinctly shorter or narrower than achene, 0.4–0.7(–1) × 0.4–0.6(–0.9) mm; culms acutely trigonous, rarely elliptic in cross section, to 0.75 mm wide. | Eleocharis tortilis |
| 46 | Tubercles at least as high or wide as achene, 0.9–1.7(–2.4) × 0.7–1.2(–2.2) mm; culms terete to elliptic in cross section, to 1.1(–1.5) mm wide. | Eleocharis tuberculosa |
| 47 | Achenes pale gray or greenish when mature, clearly cancellate to honeycomb-reticulate at 10–15X, each face with more than 20 longitudinal rows of small despressions; distal leaf sheaths often disintegrating; spikelets often proliferating, often with scales papery; se coastal plain. | Eleocharis vivipara |
| 47 | Achenes brown when mature, smooth or obscurely papillose, rugulose, reticulate, or cancellate at 20–30X; distal leaf sheaths persistent; spikelets proliferating or not, with scales membranous; western. | > 48 |
| 48 | Culms acutely 4-angled; spikelets often proliferating; tubercles as high as wide, 0.5–0.9 mm. | Eleocharis pachycarpa |
| 48 | Culms subterete, often with to 6 prominent ridges; spikelets not proliferating; tubercles much lower than wide, 0.1–0.3 mm. | Eleocharis bolanderi |
| 49 | Spikelets with scales 1–1.3 mm; boreal. | Eleocharis nitida |
| 49 | Spikelets with scales 1.5–4 mm; nonboreal. | > 50 |
| 50 | Rhizomes 3–5 mm thick, scales 2+ cm; achenes dark brown, finely rugulose at 20– 30X; California and Oregon. | Eleocharis decumbens |
| 50 | Rhizomes 0.4–3 mm thick, scales not more than 1 cm; achenes yellow, orange, medium brown, or green, rugulose or cancellate at 10–30X; ranges various. | > 51 |
| 51 | Floral scales narrowly acute to acuminate; culms usually clearly compressed; rhizomes with longer internodes to 2 mm, 2–3 mm thick; achenes falling with or before scales, rugulose and sometimes finely cancellate at 10–30X; widespread e of Rocky Mountains. | Eleocharis compressa |
| 51 | Floral scales rounded to acute; culms terete or angled, sometimes slightly compressed; rhizomes with longer internodes 2–30 mm, 0.3–2.5 mm thick; achenes sometimes persistent after scales fall, smooth to clearly rugulose or cancellate at 10X; ranges various. | > 52 |
| 52 | Floral scale apices in proximal 1/2 of spikelet broadly rounded, usually horizontally wrinkled and recurved; rhizomes with longer internodes 5–30 mm; achenes finely rugulose at 10–30X; California to South Carolina. | Eleocharis montevidensis |
| 52 | Floral scale apices in proximal 1/2 of spikelet rounded to acute, usually not horizontally wrinkled or recurved; achenes smooth to rugulose or cancellate at 10–30X; ranges various. | > 53 |
| 53 | Spikelets narrowly lanceoloid to cylindric; achenes brown, smooth or sometimes minutely cancellate at 20–30X; rhizomes with longer internodes 5–30 mm; Southwest. | Eleocharis parishii |
| 53 | Spikelets ovoid; achenes yellow, brown, or green, rugulose and/or cancellate at 10X; rhizomes with longer internodes 2–10 mm; eastern or widespread. | > 54 |
| 54 | Culms 0.5–1.5 mm wide; achenes 1.1–1.5 × 0.95–1.25 mm; rare, ne coast. | Eleocharis fallax |
| 54 | Culms 0.2–0.8 mm wide; achenes 0.6–1.2 × 0.45–0.9 mm; locally common, widespread. | > 55 |
| 55 | Culms with 4 or 5(–6) angles or sometimes terete, not compressed; achenes falling with or before scales, yellow, brown, or green, with 6–10(–14) horizontal ridges or depressions in each vertical series; Atlantic Coast to e Great Plains, local in California. | Eleocharis tenuis |
| 55 | Culms with (4–)5–10 angles, or terete, or sometimes compressed; achenes persistent after scales fall, yellow, orange, or stramineous, with 12–20 horizontal ridges or depressions in each vertical series; widespread, mostly northern. | Eleocharis elliptica |
| 56 | Tubercles closely resembling and merging with achene apex or sunken into a depression in achene, often rudimentary; culms with distal leaf sheath apex rounded, delicate, and usually disintegrating; tubers often present at ends of short rhizomes or among culm bases; culms to 12 cm × 0.5 mm; spikelets not proliferating. | > 57 |
| 56 | Tubercles clearly distinct from achene apex, not merging with or sunken into depression in achene, well developed; culms with distal leaf sheath apex acute to acuminate, usually firm and persistent; tubers absent; culms to 40 cm × 1.5 mm; spikelets often proliferating. | > 58 |
| 57 | Perianth bristles present or very rarely absent, the longer equaling achene or exceeding tubercle; tubers (except buds) oblong, usually markedly curved; achenes smooth or faintly rough at 30X; floral scales 6–10 per spikelet. | Eleocharis parvula |
| 57 | Perianth bristles absent or not more than 1/2 length of achene; tubers (except buds) oblong to orbicular, not markedly curved, 0.7–1.5 mm thick; achenes clearly rugulose at 10X to finely rough at 30X; floral scales 6–25 per spikelet. | Eleocharis coloradoensis |
| 58 | Floral scales all clearly distichous (but see 35. E. minima); spikelets clearly equilaterally depressed; spikelets often present at culm bases; culms to 0.4 mm wide; Southeast. | > 59 |
| 58 | Floral scales spirally arranged; spikelets terete (when young sometimes appearing laterally compressed or scales distichous); spikelets rarely present at culm bases; culms 1.1(–1.5) mm wide; ranges various, mostly Southeast. | > 61 |
| 59 | Longer floral scales in spikelet 3.5–5 mm; anthers more than 1 mm; basal spikelets usually present, bisexual; tubercles not proximally 3-lobed, not decurrent on achene angles; widespread. | Eleocharis baldwinii |
| 59 | Floral scales 2.5 mm or less; anthers less than 1 mm; basal spikelets absent, or if present, pistillate; tubercles proximally 3-lobed or not, decurrent on achene angles or not; very local. | > 60 |
| 60 | Perianth bristles shorter than to about equaling achene; tubercules clearly or obscurely proximally 3-lobed, decurrent on achene angles; rhizomes absent; spikelets proliferating; basal spikelets often present. | Eleocharis retroflexa |
| 60 | Perianth bristles equaling to much exceeding tubercle; tubercules proximally not 3-lobed, not decurrent on achene angles; rhizomes present; spikelets not proliferating; basal spikelets absent. | Eleocharis nana |
| 61 | Achenes finely reticulate or pitted-papillose at 20X; tubercles distinctly higher than wide, not more than 1/3 as wide as achene; plants tufted, annual, without rhizomes or stolons; spikelets not proliferating; Northeast, disjunct in Montana. | Eleocharis intermedia |
| 61 | Achenes smooth, or cancellate, or honeycomb-reticulate; tubercles not higher than wide, more than 1/3 higher than achene; plants tufted annuals or rhizomatous perennials, stolons present in some species; spikelets often proliferating; Southeast to Texas, rarely to Michigan. | > 62 |
| 62 | Spikelets with scales papery to cartilaginous, rarely membranous; achenes pale to blackish brown, 0.8–1 × 0.7–0.8 mm, smooth at 30X; tubercle 1/3 or less as wide as achene; plants perennial, with creeping rhizomes; spikelets not proliferating. | Eleocharis albida |
| 62 | Spikelets with scales membranous, or if scales papery then plants with caudexlike rhizomes mostly hidden by culm bases; achenes colorless, whitish, pale brown, or greenish, rarely red-brown, 0.5–0.8 × 0.3–0.6 mm, smooth to markedly sculptured; tubercles mostly more than 1/3 as wide as achene; plants annual or perennial, rarely with rhizomes; spikelets in some species often proliferating. | > 63 |
| 63 | Plants with rhizomes ascending, caudexlike, mostly hidden by crowded culms; achenes 0.6–1.7(–2.4) mm, cancellate or honeycomb-reticulate at 10X; spikelets with scales papery to membranous, not proliferating; culms to 1.1(–1.5) mm wide. | > 64 |
| 63 | Plants with rhizomes absent or creeping, not hidden by culms; achenes 0.45–0.8 mm, smooth or finely pitted at 30X; spikelets with scales membranous, often proliferating in some species; culms to 0.6 mm wide. | > 66 |
| 64 | Achenes 0.9–1.7 mm, coarsely cancellate at 10X, each face with 8–10 longitudinal rows of large depressions; spikelets with scales papery, seldom membranous, not proliferating; distal leaf sheaths persistent; spikelets never proliferating. | > 65 |
| 64 | Achenes 0.45–0.9 mm, finely honeycomb-reticulate at 10–20X, each face with more than 20 longitudinal rows of evident cells; spikelets with scales usually membranous, seldom papery; distal leaf sheaths often disintegrating; spikelets often proliferating. | Eleocharis vivipara |
| 65 | Tubercles distinctly shorter or narrower than achene, 0.4–0.7(–1) × 0.3–0.7(–1) mm; culms acutely trigonous, seldom elliptic in cross section, to 0.5(–1) mm wide. | Eleocharis tortilis |
| 65 | Tubercles as wide and high as achene or higher, 0.9–1.7(–2.4) × 0.7–1.2(–2.2) mm; culms terete or cross section elliptic, to 1.1(–1.5) mm wide. | Eleocharis tuberculosa |
| 66 | Spikelets with floral scales 1–1.2 mm; perianth bristles absent; spikelets not proliferating; plants tufted, not mat-forming; stolons and rhizomes absent. | Eleocharis nigrescens |
| 66 | Spikelets with floral scales 1.3–2.2 mm; perianth bristles usually present; spikelets often proliferating; plants tufted or mat-forming; stolons often present, rhizomes rarely present. | > 67 |
| 67 | Spikelets with proximal scale persistent, clearly different from floral scales, usually longer and often resembling involucral bract, often with excurrent midrib; perianth bristles present or absent, vestigial to equaling achene. | > 68 |
| 67 | Spikelets with proximal scale deciduous or sometimes persistent on some spikelets, similar to floral scales or smaller; perianth bristles present, slightly shorter than achene to exceeding tubercle. | > 69 |
| 68 | Apex of proximal scale subacute to acute, perianth bristles vestigial to equaling achene or apparently absent. | Eleocharis microcarpa |
| 68 | Apex of proximal scale rounded; perianth bristles shorter than achene or absent. | Eleocharis brittonii |
| 69 | Perianth bristles red-brown, equaling to greatly exceeding tubercle; rhizomes present; achenes not spotted; spikelets not proliferating. | Eleocharis nana |
| 69 | Perianth bristles colorless to stramineous, slightly shorter than to equaling tubercle; rhizomes absent; achenes sometimes clearly spotted olive or brown; spikelets often proliferating. | Eleocharis minima |