| | 1. Leaves of 2 forms, basal < and generally wider than cauline, rosette well developed, generally persistent |
| |
| | 2. Spikelet 3–3.5 mm, 1–2 mm wide; upper glume 9-veined, lower glume acuminate |
| P. oligosanthes var. scribnerianum |
| | 2' Spikelet 1–2.5 mm, slightly < 1 mm wide; upper glume 7-veined, lower glume acute |
| P. acuminatum |
| | 3. Leaf blade and sheath hairy |
| var. acuminatum |
| | 3' Leaf blade and sheath glabrous |
| var. lindheimeri |
| | 1' Leaves gradually reduced upward, basal rosette not well developed |
| |
| | 4. Upper floret lemma with crescent-shaped scar at base |
| P. hillmanii |
| | 4' Upper floret lemma not scarred at base |
| |
| |
| | 6. Spikelet 2.5–3 mm, glabrous; upper floret lemma with flat margin; ligule membranous, ciliate |
| P. antidotale |
| | 6' Spikelet 5–7.5 mm, short-hairy; upper floret lemma with inrolled margin; ligule short-hairy |
| P. urvilleanum |
| |
| | 7. Spikelet 4.5–5.5 mm; leaf base minutely lobed |
| P. miliaceum |
| | 7' Spikelet 2–3.5 mm; leaf base not lobed |
| |
| | 8. Spikelet axis visible, ± elongated between glumes and between florets; lower glume 1.5–2.5 mm |
| P. hirticaule |
| | 8' Spikelet axis not elongated, not clearly visible; lower glume 1–1.5 mm |
| |
| | 9. Lower glume ± 1/2 spikelet length; ultimate inflorescence branches spreading; stem nodes short-hairy |
| P. capillare |
| | 9' Lower glume < 1/3 spikelet length; ultimate inflorescence branches appressed; stem nodes glabrous |
| P. dichotomiflorum
|