| 1. | Glumes 2-3 mm long | A. whitei (QLD) |
| Glumes 3-7 mm long | 2 | |
| 2. | Awn attached just above middle of lemma | 3 |
| Awn attached well above middle of lemma | 7 | |
| 3. | Lemmas 7-10 in number, 3.5-4 mm long | A. fluitans (NSW VIC) A. gracilis |
| Lemmas 4-7 in number, more than 6 mm long | 4 | |
| 4. | Plant weakly rhizomatous; apex of leaf blade almost pungent |
A. sinuatus (NSW VIC SA TAS) |
| Plant densely tufted; apex of leaf blade long and slender | 5 | |
| 5. | Glumes narrow, lower 3-4 mm long, upper 4-5 mm long | A. neesii (NSW VIC TAS) |
| Glumes broad, lower c. 4 mm long, upper to 7 mm long | 6 | |
| 6. | Lemma evenly tapering from body of lemma | A. nervosus (NSW VIC SA WA) |
| Lemma with drawn out, chartaceous apex | A. macrorhinus (NSW VIC TAS SA WA) | |
| 7. | Lemma apex with nerves extending into bristles | 8 |
| Lemma apex with nerves not extending into bristles | 9 | |
| 8. | Lemma (excluding awn and bristles) at least 6 mm long | A. archeri (VIC TAS SA) A. archeri var. papillosus |
| Lemma (excluding awn and bristles) up to 5.5 mm long | A. vickeryae (WA) | |
| 9. | Lemma densely hispid | A. recurvatus (VIC TAS SA) |
| Lemma scabrous or papillose | A. pithogastrus (NSW VIC) |
Key to Amphibromus derived from Jacobs & Lapinpuro 1986
Taxonomic name: