Leaves with ligule absent from upper leaves, sometimes ciliate on lower leaves; blade rolled in bud.
Spikelets plano-convex, 2 or 3 together or clustered mostly on 1 side of branch, usually stiffly hispid, falling entire; florets 2, lower sterile or male, upper bisexual. Glumes unequal, ± hispid on nerves; lower c. 50% of spikelet length, 3–5-nerved, apex often mucronate; upper subequal to spikelet, apex mucronate or with a short awn, convex on back, 5–7-nerved. Lemmas 2; lower equal to or longer than upper glume (excluding cusps and awns). Back of fertile lemma adaxial, apex apiculate or obtuse. Paleas 2; lower equal to lemma; upper subequal to lemma. Lodicules 2, cuneate, fleshy. Stamens 3.
| | Key to the genus Echinochloa | |
| 1 | Ligules on at least lower leaves a fringe of long stiff hairs; either stout reed-like perennials to c. 4.5 m tall with long rhizomes, or decumbent aquatic or semi aquatic perennials to c. 2 m tall | 2 |
| 1* | Ligules of lower leaves usually absent or minutely pubescent, sometimes ciliate; tufted annuals to c. 3 m tall, usually neither as stout not as decumbent as the preceding | 3 |
| 2 | Stout, reed-like perennials c. 4.5 m tall with long rhizomes; spikelets 3-4.5 mm long; fertile lemma 2.7-3 mm long | Echinochloa pyramidalis |
| 2* | Decumbent aquatic or semi-aquatic perennials to c. 2 m tall; spikelets 4.5-6 mm long; fertile lemma 2.5-5 mm long | Echinochloa polystachya |
| 3 | Glumes and lower lemma without small spines, almost smooth between the nerves and scabrous between the nerves; primary axis of inflorescence and raceme axes smooth (sometimkes minutely scabrous on the angles); branch bristles absent; rather few spikelets on racemes | Echinochloa lacunaria |
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| 3* | Upper glume and/or lower lemma with small spines or hispid on nerves and scabrous between the nerves; primary axis of inflorescence and raceme axes scabrous, bristles usually present; spikelets more or less crowded | 4 |
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| 4 | Racemes crowded with spikelets, inflorescences very compact; spikelets broad-elliptic, 3–4.5 mm long, awnless, grain plump; upper part of fertile floret exposed at maturity | 5 |
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| 4* | Racemes less crowded and spikelets usually to 1 side; spikelets elliptic to ovate, 2.5–7 mm long, awned or awnless; grain less plump; fertile floret not exposed at maturity | 5 |
| 5 | Spikelets always pale, usually obtuse at maturity; grain whitish; cultivated | Echinochloa frumentacea |
| 5* | Spikelets purplish to blackish brown, shortly acute; grain brownish | Echinochloa esculenta |
| 6 | Spikelets 4–7 mm long; axis of inflorescence more or less horizontal at maturity with racemes drooping but plants erect; mature grain usually 2.5–3 mm long | Echinochloa oryzoides |
| 6* | Spikelets to 5 mm long; axis of inflorescence not horizontal at maturity, racemes erect, spreading or drooping | 7 |
| 7 | Shining back of fertile lemma acuminate, narrowing evenly and gradually into a long, greenish tip; nerves of upper glume and lower lemma with spreading spines with conspicuous swollen bases | Echinochloa microstachya |
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| 7* | Shining back of fertile lemma abruptly and obtusely different from short, scabrous tip; nerves of upper and lower lemma with tubercle-based bristles, usually not widely spreading or with conspicuously swollen bases | 8 |
| 8 | Spikelets 2–3 mm long; inflorescence usually less than 2 cm wide | 9 |
| 8* | Spikelets 3–5 mm long; inflorescence more than 2 cm wide | 10 |
| 9 | Spikelets 2–3 mm long, inflorescence usually <2 cm wide | Echinochloa colona |
| 9* | Spikelets 2.5–3 mm long, awned or not, conspicuously arranged in rows; bristles on axes of inflorescence few–numerous | Echinochloa crus-galli |
| 10 | Spikelets on short, rigid branches 1–4 cm long, rarely awned; nerves of lower lemma scabrous; bristles on axes of inflorescence absent or few | Echinochloa turneriana |
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| 10* | Spikelets on branches to 10 cm long, awned or not; nerves of lower lemma spinulose with tubercle-based hairs; bristles on axes of inflorescence few–numerous | 11 |
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| 11 | Main axis of inflorescence with few bristles at nodes | 12 |
| 11* | Main axis of inflorescence with numerous bristles at nodes | 13 |
| 12 | Inflorescence erect, branches not usually wavy; awns if present to 5 cm long | Echinochloa crus-galli |
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| 12* | Inflorescence more or less drooping with slender, wavy branches; awn, if present, to 3 cm long | Echinochloa inundata |
| 13 | Upper glume awnless; lower lemma with an awn to 10 mm long; inflorescence drooping with slender, wavy branches | Echinochloa crus-pavonis |
| 13* | Upper glume often with an awn to 7 mm long; lower lemma usually with an awn to 5 cm long; inflorescence erect or slightly drooping | 14 |
| 14 | Fertile floret narrow-elliptic, 3–4.2 mm long; grain oblong to oblong-ovate, 1.8–2.3 mm long | Echinochloa telmatophila |
| 14* | Fertile floret broad-ovate to elliptic, 2.5–4 mm long; grain circular to ovate, 1.4–2 mm long | Echinochloa crus-galli# |
