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1 None of the spikelets subtended by a stiff bristle |
1 Terminal spikelet on each branch subtended by a single bristle (other spikelets also sometimes so subtended) |
2 Most spikelets other than the terminal lacking a subtending bristle; leaves flat or plicate. |
3 Blades flat, 2-5 mm wide; only terminal spikelet of each branch with a subtending bristle |
3 Blades plicate, 10-80 mm wide; a single bristle sometimes present below non-terminal as well as terminal spikelets. |
4 Annual; leaves 10-25 mm wide |
4 Perennial; leaves 20-80 mm wide |
2 All spikelets subtended by 1 or more bristles; leaves flat. |
5 Bristles 4-12 below each spikelet. |
6 Annual, with fibrous roots. |
7 Spikelets 2.0-2.5 mm long; bristles reddish |
7 Spikelets 3.0-3.4 mm long; bristles yellow |
6 Perennial, noticeably rhizomatous. |
8 Panicle 3-8 (10) cm long; plant from knotty rhizomes; [native, common (sometimes weedy)] |
8 Panicle 5-25 cm long; plant from thick rhizomes; [ exotic, rare] |
5 Bristles 1-3 (rarely 6) below each spikelet. |
9 Bristles retrorsely scabrous. |
10 Leaves strigose on the lower surface; sheath margins glabrous; panicles 2-6 cm long |
10 Leaves scabrous on the lower surface; sheath margins ciliate; panicles 5-15 cm long |
9 Bristles antrorsely scabrous |
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12 Upper lemmas smooth and shiny (occasionally with obscure rugosity) |
13 Culms to 1 m tall; spikelets ca. 3 mm long; [ exotic, of ruderal sites] |
13 Culms to 6 m tall; spikelets ca. 2 mm long; [native, of marshes] |
12 Upper lemmas distinctly transversely rugose, dull. |
14 Upper lemmas coarsely rugose; leaves 4-7 mm wide; [native] |
14 Upper lemmas finely rugose; leaves 4-25 mm wide; [ exotic, generally of ruderal sites]. |
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15 Panicles densely spiciform; rachises not visible, villous. |
16 Leaves softly pilose on the upper surface; panicles arching and drooping from the base; spikelets 2.5-3.0 mm long |
16 Leaves scabrous on the upper surface; panicles nodding only at the tip; spikelets 1.8-2.2 mm long. |
17 Panicles 10-20 cm long; culms 10-25 dm tall; leaves 10-25 mm wide |
17 Panicles 3-8 cm long; culms 2-10 dm tall; leaves 4-12 mm wide |