| 1. | Ligule a fringe of long stiff hairs; plants perennial | 2 |
| Ligule absent or with cilia to 1.5 mm long; plants annual | 4 | |
| 2. | Spikelets awnless | *E. pyramidalis (WA) |
| Spikelets mucronate or awned | 3 | |
| 3. | Culms less than 1 m tall; upper leaf blades less than 10 mm wide | E. picta (QLD) |
| Culms to 3.6 m tall; upper leaf blades to 20 mm wide |
*E. polystachya (NT QLD) E. praestans auct. |
|
| 4. | Inflorescence axis ±smooth; glumes and lower lemma ±smooth and lightly scabrous on nerves |
E. lacunaria (NSW SA) |
| Inflorescence axis ±strongly scabrous; glumes and lower lemma ±scabrous both on and between nerves |
5 | |
| 5. | Spikelets at maturity very turgid and subglobose | 6 |
| Spikelets at maturity less turgid and subglobose | 8 | |
| 6. | Spikelets c. 4.5 mm long; lower lemma with a median longitudinal groove | E. turneriana (NSW NT SA QLD) |
| Spikelets c. 4 mm long; lower lemma without a median longitudinal groove | 7 | |
| 7. | Spikelets pallid; grain whitish | *E. frumentacea (NSW VIC TAS WA QLD) |
| Spikelets purplish to blackish-brown; grain brownish | *E. esculenta (NSW VIC TAS SA WA QLD) E. utilis |
|
| 8. | Mature grain 2.5-3.5 mm long | 9 |
| Mature grain less than 2.5 mm long | 11 | |
| 9. | Spikelets without well-developed anthocyanin pigmentation; upper floret 3.5-4.5 mm long |
*E. oryzoides (NSW WA) |
| Spikelets with well-developed anthocyanin pigmentation; upper floret 4.5-6.5 mm long |
10 | |
| 10. | Upper floret 5-6.5mm long; anthers 1.5-2.1 mm long | E. kimberleyensis (NT WA QLD) |
| Upper floret 4.5-5mm long; anthers 2.5-2.8 mm long | E. macrandra (WA) | |
| 11. | Upper glume noticably awned | 12 |
| Upper glume not or scarcely awned | 14 | |
| 12. | Upper glume with awns c. 3.5 mm long | E. dietrichiana (NT SA QLD) |
| Upper glume with awns up to 7mm long | 13 | |
| 13. | Spikelets 3-4.2 mm long, with purplish awns | E. telmatophila (NSW WA QLD) E. walteri auct. |
| Spikelets 4-4.5 mm long, with pale awns | E. elliptica (NT WA QLD) | |
| 14. | Inflorescence drooping with soft flexuous branches; racemes compound |
*E. crus-pavonis (NSW SA WA QLD) |
| Inflorescence usually erect with branches stiffly spreading; racemes simple |
15 | |
| 15. | Upper floret apex gradually narrowing into a firm tip to 1.5 mm long |
*E. muricata var. microstachya (NSW VIC) E. microstachya |
| Upper floret apex abruptly terminating in a fragile tip to 0.5 mm long |
16 | |
| 16. | Spikelets 3.5-5mm long excluding cusps and awns when present | E. inundata (NSW SA QLD) |
| Spikelets less than 3.5 mm long | 17 | |
| 17 | Spikelets awnless to cuspidate, close together in 4 irregular rows; grain 1.1-1.2 mm wide, whitish |
*E. colona (NSW VIC NT SA WA QLD) |
| Spikelets awnless to strongly awned, not in 4 rows; grain 1.2-1.6 mm wide, pale brownish | *E. crus-galli (NSW VIC TAS NT SA WA QLD) E. crus-galli subsp. hispidula |
Key to Echinochloa derived from Vickery 1975; Michael 1983; Webster 1987;
Scholz 1992
Taxonomic name: