| 1. | Leaf blades plicate | 2 |
| Leaf blades not plicate | 3 | |
| 2. | Robust perennial | *S. palmifolia (NSW NT SA WA QLD) |
| Decumbent annual | *S. barbata (QLD) | |
| 3. | Bristles retrorsely barbed | *S. verticillata (NSW VIC TAS NT SA WA QLD) S. adhaerens, S. carnei |
| Bristles antrorsely barbed | 4 | |
| 4. | Annuals | 5 |
| Perennials | 12 | |
| 5. | Inflorescence an open to contracted panicle of racemes | 6 |
| Inflorescence a tightly contracted false spike | 7 | |
| 6. | Inflorescence contracted | *S. italica (NSW VIC TAS SA WA QLD) |
| Inflorescence open | *S. dielsii (NT SA WA QLD) | |
| 7. | Upper glume 1/2 spike length | 8 |
| Upper glume more than 1/2 spike length | 9 | |
| 8. | Spikelets less than 2.5 mm long | *S. pumila subsp. subtesselata (NSW NT QLD) S. pallide-fusca |
| Spikelets c. 3 mm long | *S. pumila subsp. pumila (NSW VIC SA WA QLD) S. glauca, S. lutescens |
|
| 9. | Spikelets not turgid; upper floret very finely rugose | *S. viridis (NSW VIC TAS SA QLD) |
| Spikelets turgid; upper floret coarsely rugose | 10 | |
| 10. | Spikelets more than 3.5 mm long |
S. queenslandica (NT WA QLD) |
| Spikelets up to 3.4 mm long | 11 | |
| 11. | Spikelets 2.5-2.9 mm long; upper glume 3/4 spikelet length | S. surg ens (NSW NT WA QLD) S. brownii |
| Spikelets 3-3.4 mm long; upper glume from 80% to almost as long as spikelet | S. apiculata (NT WA QLD) | |
| 12. | Inflorescence a loosely contracted panicle | 13 |
| Inflorescence a tightly contracted false spike | 15 | |
| 13. | Inflorescence with spikelets clustered along primary branches | S. oplismenoides (NT QLD) |
| Inflorescence with spikelets ±uniformly arranged | 14 | |
| 14. | Spikelets c. 4 mm long | S. australiensis (NSW NT QLD) |
| Spikelets c. 3 mm long | S. paspalidioides (NSW QLD) | |
| 15. | Inflorescence (excluding bristles) c. 4 mm wide | *S. parviflora (NSW VIC TAS SA WA QLD) S. geniculata var. geniculata, S. geniculata var. pauciseta, S. gracilis var. gracilis, S. gracilis var. pauciseta |
| Inflorescence (excluding bristles) c. 6-8mm wide | 16 | |
| 16. | Bristles purple; upper glume 7-nerved | *S. incrassata (NT WA QLD) S. porphyrantha |
| Bristles fulvous; upper glume 3-5-nerved | 17 | |
| 17. | Inflorescence 7-25cm long; leaf blades 3-10 mm wide | *S. sphacelata var. anceps (NSW WA QLD) S. anceps |
| Inflorescence 20-50cm long; leaf blades 10-17 mm wide | *S. sphacelata var. splendida (QLD) S. splendida |
Key to Setaria derived from Vickery 1975; Webster 1987
Taxonomic name: