| 1. | Upper glume 9-13-nerved; fertile floret curved in profile |
2 |
| Upper glume 5-7(-9) nerved; fertile floret not curved in profile |
3 | |
| 2. | Spikelets 2-2.7mm wide | P. globoideum (NSW QLD) |
| Spikelets 1.4-1.5mm wide | P. retiglume (NT WA QLD) | |
| Spikelets 1-1.1mm wide | P. reflexum (NT SA WA) | |
| 3. | Racemes reduced to 1 or 2 spikelets | P. rarum (NSW NT WA QLD) |
| Racemes not reduced | 4 | |
| 4. | Spikelets irregularly arranged on raceme axes |
5 |
| Spikelets regularly arranged on raceme axes |
12 | |
| 5. | Annuals with compressible culms | 6 |
| Perennials with wiry or setaceous culms |
7 | |
| 6. | Spikelets 2-2.4mm long; culms smooth | P. clementii (NSW NT SA WA QLD) |
| Spikelets 2.75-3.1mm long; culms ±scabrous |
P. basicladum (NT SA WA QLD) | |
| 7. | Spikelets up to 1mm wide | P. criniforme (NSW QLD) P. gracile var. debile |
| Spikelets more than 1mm wide | 8 | |
| 8. | Spikelets acute; lower lemma deeply grooved longitudinally |
P. tabulatum (WA) |
| Spikelets obtuse; lower lemma without a groove |
9 | |
| 9. | Culms woody, arising from robust rhizomes; spikelets c. 4mm long |
P. grandispiculatum (QLD) |
| Culms herbaceous, arising from contracted rootstocks; spikelets 2-3.5mm long |
10 | |
| 10. | Inflorescence up to 3cm long with up to 10 spikelets |
P. spartellum (QLD) |
| Inflorescence much more than 3cm long with many more than 10 spikelets |
11 | |
| 11. | Culms bluish-green; spikelets 2.25-3.5mm long; leaves not filiform |
P. constrictum (NSW VIC NT SA WA QLD) P. gracile var. rugosum |
| Culms bright green; spikelets 2-2.75mm long; leaves filiform |
P. gracile (NSW VIC NT SA WA QLD) | |
| 12. | Spikelets more than 2.5mm long | 13 |
| Spikelets less than 2.5mm long | 17 | |
| 13. | Lower racemes often as long as or longer than internodes of main axis between them |
P. jubiflorum (NSW VIC NT SA WA QLD) |
| Lower racemes shorter than internodes of main axis between them |
14 | |
| 14. | Leaf sheaths ciliate on at least one margin in upper part |
15 |
| Leaf sheaths glabrous on margins | 16 | |
| 15. | Rigid wiry perennial; leaf blades firmly rigid |
P. gausum (NSW QLD) |
| Lax decumbent perennial; leaf blades soft |
P. aversum (NSW QLD) | |
| 16. | Culms thick and spongy; racemes 10-16 | P. udum (NT QLD) |
| Culms slender and not spongy; racemes 3-8 |
P. flavidum (QLD) | |
| 17. | Leaf sheaths and blades hirsute | P. albovillosum (NSW QLD) P. radiatum var. hirsutum |
| Leaf sheaths and blades glabrous | 18 | |
| 18. | Leaves distinctly scabrous; rachis relatively broad |
P. scabrifolium (QLD) |
| Leaves not scabrous; rachis narrow | 19 | |
| 19. | Leaf blades narrow and rolled | P. caespitosum (NSW QLD) |
| Leaf blades flat, up to 4mm wide | 20 | |
| 20. | Fertile floret coarsely transversely rugulose |
P. disjunctum (NT QLD) P. breviflorum |
| Fertile floret finely transversely rugulose |
P. distans (NSW NT WA QLD) P. radiatum |
Key to Paspalidium derived from Vickery 1975; Webster 1987; Webster 1995 (as Setaria)
Taxonomic name: