| 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 2-2.7 mm wide |
P. globoideum (NSW QLD) Setaria globoidea |
| Spikelets 1.4-1.5 mm wide |
P. retiglume (NT WA QLD) Setaria retiglumis |
|
| Spikelets 1-1.1 mm wide |
P. reflexum (NT SA QLD WA) Setaria reflexa |
|
|
3.
4. |
Racemes reduced to 1-2 (-4) spikelets | 4 |
| Racemes not reduced | 5 |
|
| Spikelets 2.7-3.5 mm long |
P. rarum (NSW NT QLD WA) Setaria rara |
|
| Spikelets 2.1-2.5 mm long | P. johnsonii (QLD) | |
| 5. | Spikelets irregularly arranged on raceme axes | 6 |
| Spikelets regularly arranged on raceme axes | 14 | |
| 6. | Annuals with compressible culms | 7 |
| Perennials with wiry or setaceous culms | 8 | |
| 7. | Spikelets 2-2.4 mm long; culms smooth |
P. clementii (NSW NT SA WA QLD) Setaria clementii |
| Spikelets 2.75-3.1 mm long; culms ±scabrous |
P. basicladum (NT SA WA QLD) Setaria basiclada |
|
| 8. | Spikelets up to 1 mm wide | P. criniforme (NSW QLD) P. gracile var. debile, Setaria criniformis |
| Spikelets more than 1 mm wide | 9 | |
| 9. | Lower lemma deeply grooved longitudinally | P. tabulatum (WA) |
| Lower lemma without a groove | 10 | |
| 10. | Culms arising from robust rhizomes; spikelets 4.1-4.8 mm long | P. grandispiculatum (QLD) |
| Culms arising from contracted rootstocks; spikelets 2.4-3.6 mm long | 11 | |
|
11.
12. |
Upper lemma surface finely rugulose |
12 |
| Upper lemma surface coarsely rugose |
13 |
|
| Culms wiry and branched, not bushy, 50-115 cm tall; ligule c. 0.3 mm long, leaf blades flat or sometimes rigid to inrolled |
P. spartellum (QLD) Setaria spartellum |
|
| Culms bushy, 30-90 cm tall; ligule c. 1mm long; leaf involute and becoming fililiform |
P. gracile (NSW VIC NT SA WA QLD) | |
| 13. | Upper lemma surface moderately coarsely rugose; spikelets 2.4-3.6 mm long |
P. constrictum (NSW VIC NT SA WA QLD) P. gracile var. rugosum, Setaria constricta |
| Upper lemma very coarsely rugose (the wrinkles visible through the upper glume); spikelets 1.8-2.3 mm long |
P. breviflorum (NSW QLD) | |
| 14. | Spikelets at least 2.5 mm long | 15 |
| Spikelets less than 2.5 mm long | 19 | |
| 15. | Most inflorescence branches, particularly those toward the apex of the inflorescence, often as long as or longer than adjacent internodes of axis |
P. jubiflorum (NSW VIC NT SA WA QLD) |
| Most inflorescence branches shorter than adjacent internodes of axis |
16 | |
| 16 | Leaf sheaths ciliate on at least one margin in upper part | 17 |
| Leaf sheaths glabrous on margins | 18 | |
| 17. | Rigid wiry perennial; leaf blades firmly rigid | P. gausum (NSW QLD) |
| Lax decumbent perennial; leaf blades soft | P. aversum (NSW QLD) | |
| 18. | Culms thick and spongy; racemes 10-16 | P. udum (NT QLD) |
| Culms slender and not spongy; racemes 3-8 | P. flavidum (QLD) | |
| 19. | Leaf sheaths and blades hirsute | P. albovillosum (NSW QLD) P. radiatum var. hirsutum |
| Leaf sheaths and blades glabrous | 20 | |
|
20.
21. |
Leaf blades narrow and rolled (when dry) |
P. caespitosum (NSW QLD) |
| Leaf blades remaining flat, up to 4 mm wide |
21 |
|
| Leaf blades scabrous; raceme rachis relatively broad | P. scabrifolium (QLD) | |
| Leaf blades not scabrous; raceme rachis relatively narrow |
P. radiatum, Setaria distans, P. disjunctum |
Key to Paspalidium derived from Vickery 1975; Webster 1987
Taxonomic name: