| 1. | Base of joint and pedicel producing a distinct pore | 2 |
| Base of joint and pedicel without a pore | 4 | |
| 2. | Leaf blades narrow; inhabits rocky cliffs | I. sp. (George Creek I.D.Cowie+ 5306) (NT) |
| Leaf blades broad; inhabits swamps | 3 | |
| 3. | Inflorescence of many digitate racemes | I. polystachyum (QLD) |
| Inflorescence of 2-3 racemes | I. tropicum (NT QLD) | |
| 4. | Lower glume of sessile spikelet transversely rugose | 5 |
| Lower glume of sessile spikelet not transversely rugose | 6 | |
| 5. | Pedicelled spikelet developed | I. rugosum var. rugosum (NT QLD) |
| Pedicelled spikelet much reduced | I. rugosum var. segetum (NT QLD) | |
| 6. | Decumbent or stoloniferous habit | 7 |
| Erect habit | 9 | |
| 7. | Annual with mature inflorescence to 2 cm long and leaf blades to 5 mm wide | I. decumbens (NT QLD) |
| Perennials with mature inflorescence more than 2 cm long and leaf blades more than 6 mm wide | 8 | |
| 8. | Stoloniferous | I. muticum (QLD) |
| Decumbent, without stolons | I. triticeum (NSW QLD) | |
| 9. | Raceme single | 10 |
| Racemes paired | 11 | |
| 10. | Sessile spikelet c. 10mm long, with silky hair | I. albovillosum (WA) |
| Sessile spikelet 6-7mm long, glabrous | I. fragile (QLD) I. baileyi, Digastrium fragile |
|
| 11. | Lower glume with transverse undulations | I. barbatum (NT) |
| Lower glume smooth | 12 | |
| 12. | Nodes glabrous | I. australe var. arundinaceum (NT WA QLD) I. arundinaceum |
| Nodes hairy | 13 | |
| 13. | Leaves, rachis internodes and pedicels hairy | I. australe var. villosum (NT QLD) I. villosum |
| Leaves, rachis internodes and pedicels glabrous | I. australe var. australe (NSW NT WA QLD) |
Key to Ischaemum derived from Bentham 1878; Simon 1989b
Taxonomic name: