Inflorescence a terminal, ebracteate, single spikelet, sometimes proliferating. Spikelet terete or angular, rarely compressed, few–many-flowered; rachilla persistent. Glumes spirally arranged, sometimes subdistichous, caducous. Flowers bisexual. Hypogynous bristles 6–10, smooth or retrorsely or rarely antrorsely scabrous or toothed, sometimes reduced, rarely absent. Stamens 1–3. Style 2- or 3-fid, usually glabrous, articulated with the nut, the dilated base persistent on the nut.
Nut trigonous or lenticular, obovoid, globose or pyriform, sometimes with a narrow neck just below the apex, crowned by the enlarged style base.
Some species are used for matting. E. dulcis is cultivated for its edible tubers (Chinese Water Chestnut). The record of the trop. species E. nuda C. B. Clarke from this State (NT) is apparently erroneous. Note: nut length measurements do not include the persistent style base. Treatment based on Blake (1939).
| | Key to the species | |
| 1 | Glumes leathery, finely many-nerved with distinct midrib, not at all or only obscurely keeled, spikelet not much broader than culm | 2 |
| Glumes membranous with distinct midrib, often distinctly keeled, sides nerveless; spikelet much broader than culm unless the latter is flat | 6 |
| 2 | Culms longitudinally septate internally as well as transversely septate (septa not obvious externally) | 3 |
| Culms transversely septate only, obvious externally at least when dried
Back to 1 | 4 |
| 3 | Culms 4- or 5-angled | Eleocharis philippinensis |
| Culms terete
Back to 2 | Eleocharis obicis |
| 4 | Culms usually dark green, in a close linear series on a stout horizontal rhizome; in mature culms, some septa much stouter than the rest; glumes 7–11 mm long, usually with a dark red band inside the hyaline margins; nut 2–2.7 mm long; bristles 8–10 | Eleocharis sphacelata |
| Culms yellow-green, tufted (rhizome occasionally present but then slender and ascending with culms tufted along it); all septa similar in texture; glumes 5–6.5 mm long, without dark red band inside hyaline margins; nut 1.5–2 mm long; bristles 6–8
Back to 2 | 5 |
| 5 | Inflorescence gradually tapering to apex; exposed portion of glumes mostly 2.5–4.5 mm long, usually longer than wide; glumes relatively long and narrow, 6–6.5 mm long, 2.5–3 mm wide, with hyaline margin 0.2–0.3 mm wide; nut c. 1.5–1.8 mm long, 1–1.5 mm diam., golden brown; bristles 6–8, united at the base, with teeth slender and irregularly retrorse; anthers 2.5–3 mm long, with apical appendage 0.1–0.2 mm long | Eleocharis dulcis |
| Inflorescence very sharply tapered to apex (almost truncate); exposed portion of glumes 1.5–2.5 mm long, usually broader than long; glumes relatively broader, 5–5.5 mm long, c. 4 mm wide, with hyaline margins 0.1–0.2 mm wide; nut c. 2 mm long, 1.5–1.9 mm diam., pale yellow-brown; bristles 6 or 7, free, slender, regularly and strongly retrorsely toothed; anthers 2–2.5 mm long, with apical appendage 0.3–0.4 mm long
Back to 4 | Eleocharis equisetina |
| 6 | Style 3-fid, or rarely 2-fid in Eleocharis pallens and then the uppermost leaf sheath is truncate and prominently mucronate at the summit | 7 |
| Style 2-fid; mouth of leaf sheath never mucronate
Back to 1 | 20 |
| 7 | External surface of the nut longitudinally ridged, the intervening cells transversely linear or oblong; nut obscurely trigonous or terete; leaf sheaths membranous, with mouth oblique (often loose or difficult to observe), not dilated or thickened | 8 |
| Surface of nut finely reticulate, wrinkled, pitted or smooth, the cells very small and often very faint, mostly shortly vertically oblong in very numerous series; nut trigonous or lenticular; uppermost leaf sheath thickened and differentiated at the oblique or transverse mouth
Back to 6 | 11 |
| 8 | Stamens 1 or 2; bristles on nut 6 or 7, and nearly as long as nut | Eleocharis parodii |
| Stamens 3; bristles on nut few, small or absent
Back to 7 | 9 |
| 9 | Nut pyriform, with c. 8 prominent ridges on each face | Eleocharis macbarronii |
| Nut narrow-obovoid to obovoid, with 3–5 prominent ridges on each face
Back to 8 | 10 |
| 10 | Spikelet ovoid, 2–7 mm long, usually setting fruit; glumes 2.0–2.5 mm long; plants neither proliferating nor with tubers; glumes dark red-brown to blackish | Eleocharis pusilla |
| Spikelet narrow-ovoid to linear, 10–20 mm long, rarely producing fruit; glumes 3–5 mm long; plants often proliferating, producing tubers; glumes red-brown
Back to 9 | Eleocharis atricha |
| 11 | Culms clearly 4-angled, style base about as broad as nut | 12 |
| Culms terete, angular-striate or flattened; style base a third to three-quarters as broad as nut
Back to 7 | 13 |
| 12 | Culms to 0.5 mm diam.; spikelet 4–7 mm long; bristles 4; leaf sheath with oblique mouth, rarely minutely mucronate | Eleocharis pachycarpa |
| Culms 1–1.5 mm diam.; spikelet 10–20 mm long; bristles 6–8; leaf sheath with usually transverse mouth, mucronate
Back to 11 | Eleocharis tetraquetra |
| 13 | Nut more or less equally trigonous with ribbed dorsal angle | 14 |
| Nut biconvex or plano-convex, with the dorsal angle not ribbed if present
Back to 11 | 16 |
| 14 | Nut not constricted at apex; bristles usually longer than nut; [culms not obviously septate; sheaths pale brown to pale reddish, uppermost with mouth more or less oblique, sometimes mucronate] | Eleocharis gracilis |
| Nut constricted to a very short neck below the apex; bristles three-quarters as long as to slightly exceeding nut
Back to 13 | 15 |
| 15 | Spikelet 6–9 mm long; culms 20–30 cm long, usually with partial transverse septa obvious when dried; leaf sheaths reddish, uppermost with mouth thickened, transverse and mucronate | Eleocharis dietrichiana |
| Spikelet 2–4 mm long; culms to 5 cm long, without obvious septa when dried; leaf sheaths pallid, uppermost with mouth not thickened, oblique and without a mucro
Back to 14 | Eleocharis parvula |
| 16 | Culms transversely septate (obvious externally at least when dried) | Eleocharis blakeana |
| Culms not completely transversely septate
Back to 13 | 17 |
| 17 | Rhizome creeping; nut not strongly ribbed on the angles; anthers with apical appendage c. 0.2 mm long; glumes tardily deciduous | 18 |
| Rhizome very short; culms densely tufted; nut with prominently ribbed angles; anther appendage not exceeding 0.15 mm in length; glumes readily deciduous
Back to 16 | 19 |
| 18 | Culms terete or nearly so, trigonous immediately below the spikelet (may be flattened when dried, and then mucro at mouth of leaf sheath may be in any position relative to 'margins' of 'flattened' culm); spikelet usually much broader than culm, 1.5–3 cm long, 3–7 mm diam | Eleocharis acuta |
| Culms strongly flattened when fresh even at apex; mucro at mouth of leaf sheaths always at middle of one flat face of culm; spikelet slightly broader than culm, 1–2(–4) cm long, c. 2.5 mm diam
Back to 17 | Eleocharis plana |
| 19 | Glumes acute; spikelet more or less acute, c. 2 mm diam.; culms strongly longitudinally ridged (obvious at least when dried) with surface obviously reticulate and glistening between ridges | Eleocharis pallens |
| Glumes rounded; spikelet more or less obtuse, 2.5–3 mm diam.; culms finely and faintly striate, dullish
Back to 17 | Eleocharis cylindrostachys |
| 20 | Leaf sheath firm at apex; spikelet globose to ovoid; nut black | Eleocharis geniculata |
| Leaf sheath thinly membranous, often torn at apex; spikelet ovoid or oblong-ovoid; nut pale green to dark greenish brown
Back to 6 | Eleocharis minuta |
