| | 1. Spikelets except awns > 4 mm |
| |
| | 2. Perennial; stem generally > 4.5 dm; glumes, lemma acute |
| A. pratensis |
| | 2' Annual; stem generally < 4.5 dm; glumes, lemma acute or obtuse |
| |
| | 3. Glumes ciliate on keel near base, glabrous on lateral veins, winged and appearing asymmetrical; anthers > 3.5 mm; inflorescence generally > 7 cm, tapered at both ends; leaf sheaths not inflated |
| A. myosuroides |
| | 3' Glumes ciliate on all nerves, not winged; anthers < 1.5 mm; inflorescence < 6.5 cm, not tapered; upper leaf sheaths conspicuously inflated |
| 2 A. saccatus |
| | 1' Spikelets except awns < 4 mm |
| |
| | 4. Awn straight, > lemma by 0–2 mm; perennial herb |
| A. aequalis |
| | 4' Awn bent, exceeding lemma by 1.5–5 mm; perennial herb or annual |
| |
| | 5. Spikelets > 3 mm; upper leaf sheath conspicuously inflated; awn exceeding lemma by 3–5 mm |
| 2 A. saccatus |
| | 5' Spikelets generally < 3 mm; upper leaf sheath not inflated; awn exceeding lemma by 1.5–3.5 mm |
| |
| A. carolinianus |
| | 6' Perennial; anther 1.2–2 mm |
| A. geniculatus
|