| 1. | Fertile culm internode bowed and protruding from leaf sheath with chartaceous margins; axillary spikelet with upper glume >4.8 mm long; upper glume of terminal spikelets scabrid in mid third portion |
C. johnsoniana (QLD) |
| Fertile culm internode retained within leaf sheath with margins semiwoody to woody; axillary spikelet with upper glume <4.5 mm long; upper glume of terminal spikelets sparsely hairy to pilose with simple hairs to 1 mm long in mid third portion. | 2 | |
| 2. | Lower portion of fertile leaf sheath slightly swollen to 1.4 mm wide, wall 0.2–0.3 mm thick; axillary spikelets 6–7.5 mm long (excluding awn); terminal spikelets 5–6 mm long (excluding awn) | C. cylindrosperma (QLD) |
| Lower portion of fertile leaf sheath conspicuously swollen to 2.7 mm wide, wall 0.3–0.5 mm thick; axillary spikelets 3.5–5.5 mm long (excluding awn); terminal spikelets 3–4.6 mm long (excluding awn) | 3 ( C. gracillima) | |
| 3. |
Axillary spikelets 4–5.5 mm long (excluding awn) × 1–1.1 mm wide, anthers 0.3–0.4 mm long; terminal spikelets with lower glume when present c. 0.2 mm long and upper glume apex obtuse to truncate | C. gracillima subsp. gracillima (QLD) |
Axillary spikelets 3.5–4.2 mm long (excluding awn) × 0.8–0.9 mm wide, anthers 0.4–0.7 mm long; terminal spikelets with lower glume when present 0.8–1.8 mm long and upper glume apex acute |
C. gracillima subsp. ipsviciensis (QLD) |
Key to Calyptochloa derived from Hubbard 1933; Webster 1987; Thompson & Simon 2012