| 1. | Length/width ratio of leaf blades less than 7 | 2 |
| Length/width ratio of leaf blades greater than 10 | 4 | |
| 2. | Basal racemes more than 4 cm long | O. compositus (NT QLD) |
| Basal racemes less then 2 cm long | 3 | |
| 3. | Spikelet 3.5-4 mm long; awns smooth, viscous | O. aemulus (NSW VIC QLD) O. aemulus var. lasiorhachis, O. hirtellus auct. |
| Spikelet 2-2.5 mm long; awns scaberulous, not viscous | O. burmannii (NT QLD) | |
| 4. | Racemes in distinct clusters; leaf blade indumentum dense |
O. mollis (NSW QLD) |
| Racemes not in distinct clusters; leaf blade indumentum sparse |
O. imbecillis (NSW VIC NT WA QLD) O. hirtellus subsp. imbecillis, O. undulatifolous var. imbecillis |
Key to Oplismenus derived from Vickery 1975; Scholz 1981; Simon 2010