| 1. | Lowest node of inflorescence with whorled branches | 2 |
| Lowest node of inflorescence with 1-2 branches | 10 | |
| 2. | Most inflorescence branches whorled | 3 |
| Only lowest inflorescence branch whorled | 6 | |
| 3. | Spikelets uniformly distributed in inflorescence; grain globular | S. australasicus (NT SA WA QLD) |
| Spikelets situated on apical 1/3-2/3 of inflorescence branches; grain not globular | 4 | |
| 4. | Inflorescence branches not all whorled; ligule 0.35-1 mm long; leaves broad | S. coromandelianus (NT WA QLD) |
| Inflorescence all, except uppermost, whorled; ligule c. 0.1 mm long; leaves narrow | 5 | |
| 5. | Spikelets 1.1-1.5 mm long; grain quadrangular | S. pulchellus (NT QLD) |
| Spikelets 1.6-1.8 mm long; grain lenticular | S. lenticularis (NT QLD) | |
| 6. | Inflorescence a very open panicle with small delicate uniformly distributed spikelets | S. caroli (NSW VIC NT SA WA QLD) |
| Inflorescence with spikelets ±clustered on branches | 7 | |
| 7. | Inflorescence ±open; inflorescence axis and branches distinctly scabrous |
S. scabridus (QLD) |
| Inflorescence ±arranged in false spikes; inflorescence axis and branches smooth |
8 | |
| 8. | Inflorescence branches with several false spikes ±loosely arranged | S. contiguus (NSW QLD NT) |
| Inflorescence branches with a single false spike towards apex | 9 | |
| 9. | Upper glume distinctly shorter than spikelet; inflorescence open | S. actinocladus (NSW NT SA WA QLD) |
| Upper glume as long as spikelet; inflorescence mostly closed | S. partimpatens (QLD) | |
| 10. | Upper glume ±as long as spikelet | 11 |
| Upper glume 1/4-3/4 spikelet length | 12 | |
| 11. | Stoloniferous; leaf sheaths usually shorter than internodes; spikelets 1.5-2mm long | S. mitchellii (NSW VIC NT SA WA QLD) S. benthamii |
| Rhizomatous; leaf sheaths usually longer than internodes; spikelets ±3mm long |
S. virginicus (NSW VIC TAS NT SA WA QLD) | |
| 12. | Upper glume ±1/3 spikelet length | 13 |
| Upper glume 1/2 spikelet length or more | 14 | |
| 13. | Plant coarse and tall (to 1.7m), with leaf blades to 70cm x 6-7 mm | *S. pyramidalis (NSW NT QLD) |
| Plant shorter (to 0.75m), with leaf blades to 40cm x 2.5-3.5 mm | *S. jacquemontii (NT QLD) S. pyramidalis var. jacquemontii |
|
| 14. | Inflorescence a much branched and open panicle; spikelets at least 2.5 mm long | S. pamelae (QLD) |
| Inflorescence with spikelets and branches appressed to the axis; spikelets up to 2.5 mm long | 15 | |
| 15. | Inflorescence spicate (to semi-spicate) | 16 |
| Inflorescence spreading or spikelets arranged in spike-like clusters | 18 | |
| 16. | Inflorescence branches bunched | S. disjunctus (QLD) |
| Inflorescence branches not bunched | 17 | |
| 17. | Spikelets 2.1-2.5 mm long; inflorescence branches usually appressed uniformly | *S. africanus (NSW VIC TAS NT SA WA QLD) S. capensis, S. indicus var. africanus, S. indicus var. capensis |
| Spikelets 1.6-2 mm long; inflorescence branches usually less appressed at base | *S. fertilis (NSW VIC QLD) S. indicus var. fertilis, S. indicus var. major |
|
| 18. | Lower glumes about 1/2 spikelet length; plants shortly rhizomatous |
S. latzii (NT) |
| Lower glume less than 1/2 spikelet length; plants not rhizomatous | 19 | |
| 19. | Spikelets spaced loosely and fairly evenly along inflorescence branches | 20 |
| Spikelets in spike-like clusters on inflorescence branches | 22 | |
| 20. | Spikelets 1.6-2.3 mm long | *S. natalensis (NSW NT QLD) |
| Spikelets 1.2-1.6 mm long | 21 | |
| 21. | Inflorescence branches bearing spikelets to base | S. sessilis (NSW QLD) |
| Inflorescence branches naked for some distance at base | S. laxus (NSW QLD) | |
| 22. | Inflorescence branches shorter than adjacent internodes | S. creber (NSW VIC NT SA QLD) |
| Inflorescence branches as long as or longer than adjacent internodes | 23 | |
| 23. | Leaf blades involute; leaf sheaths not distinctly fibrous at base of plant | S. elongatus (NSW SA WA QLD) |
| Leaf blades flattened; leaf sheaths distinctly fibrous at base of plant | S. blakei (NSW NT SA WA QLD) |
Key to Sporobolus derived from Simon 1982a; Baaijens and Veldkamp
1991; Simon 1993a; Simon and Jacobs 1999
Taxonomic name: