| 1. | Sterile lemmas acuminate | 2 |
| Sterile lemmas obtuse or acute | 4 | |
| 2. | Spikelet 8-12mm long | T. acuminata (NSW VIC TAS SA) |
| Spikelet 4-6mm long | 3 | |
| 3. | Leaf blades tightly inrolled |
T. oreophila var. oreophila (TAS) Ehrharta oreophila |
| Leaf blades flat |
T. oreophila var. minor (TAS) Ehrharta oreophila var. minor |
|
| 4. | Sterile lemmas scabrous | T. distichophylla (VIC TAS SA) |
| Sterile lemmas smooth | 5 | |
| 5. | Spikelets ±8mm long | T. laevis (WA) |
| Spikelets ±6mm long | 6 | |
| 6. | Leaf blades flat, more than 2 mm wide, not stiff | T. juncea (NSW VIC TAS SA QLD) |
| Leaf blades folded, less than 1 mm wide, stiff | T. turfosa (NSW VIC SA) |
Key to Tetrarrhena derived from Willis 1970; Willemse 1982 under Ehrharta; Walsh 1989
Taxonomic name: