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1 Both lower and upper glumes absent, or upper glume present on terminal spikelet only of a panicle branch. |
2 Plants stoloniferous; culms to 40 cm long; blades to 4 mm wide; spikelets 3.8-5.2 mm long, apex acuminate; upper glume sometimes present on terminal spikelet of a panicle branch |
2 Plants cespitose; culms to 200 cm long; blades to 35 mm wide; spikelets 1.8-2 mm long, apex obtuse; both glumes absent from all spikelets |
1 At least upper glume present on all spikelets. |
3 Spikelets solitary, not associated with rudimentary spikelets or naked pedicels. |
4 Panicles usually composed of a terminal pair of branches, sometimes with 1 (-5) additional branches below the terminal pair. |
5 Upper glumes pubescent on the back or margins. |
6 Spikelets 1.3-1.9 mm long; upper glumes pilose along the margins; ligules 0.5-0.8 mm long; panicle branch axis 0.2-0.8 mm wide |
6 Spikelets 2.4-3.2 mm long; upper glumes sparsely pubescent on the back; ligules 1-2 mm long; panicle branch axis 1.2-2.2 mm wide |
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7 Spikelets elliptic, the tip acute or acuminate. |
8 Plants short- rhizomatous, culms appearing cespitose; blades to 4 mm wide; spikelets 3-3.6 mm long; lower lemmas 5-veined; upper florets stramineous to golden brown; most frequently found along roadsides and in pastures |
8 Plants rhizomatous, the culms separate; blades to 8 mm wide; spikelets 3-4.5 mm long; lower lemmas 3-veined; upper florets white; most frequently found in brackish and salt marshes |
7 Spikelets ovate to broadly elliptic, the tip obtuse to broadly acute. |
9 Culms to 60 cm long; blades flat; panicle branches to 6.4 cm long; spikelets 1.9-2.3 mm long, 1.2-2 mm wide; upper glumes 3-veined |
9 Culms to 120 cm long; blades flat or longitudinally folded; panicle branches to 15 cm long; spikelets 2.5-4 mm long, 2-2.8 mm wide; upper glumes 5-veined |
 Show caption*© Kevin Faccenda, some rights reserved (CC BY), uploaded by Kevin Faccenda Panicles with 1-70 branches; if > 1, the branches arranged racemosely, the 2 uppermost not paired. |
10 Panicle branches 7-70, the axes extending beyond the outermost spikelets; panicle branches disarticulating at maturity |
 Show caption*© Greg Tasney, some rights reserved (CC BY-SA), uploaded by Greg Tasney branches 1-6, terminating in a spikelet; panicle branches persistent. |
11 Upper florets olive to dark brown |
11 Upper florets pale to tan. |
12 Axes of panicle branches not broadly winged, 0.6-1.3 mm wide. |
13 Spikelets orbicular, 2.8-3.2 mm wide |
13 Spikelets slightly longer than broad, 2.0-2.5 mm wide |
 Show caption*© Dan Johnson, some rights reserved (CC BY), uploaded by Dan Johnson of panicle branches broadly winged, 1.8-3.3 mm wide. |
14 Culms to 100 cm long; spikelets 3.2-4 mm long, 1.6-1.7 mm wide; upper lemmas with a few short hairs at their tips; caryopses 2-3 mm long |
14 Culms to 50 cm long; spikelets 1.7-2.1 mm long 1.1-1.4 mm wide; upper lemmas glabrous; caryopses 1-1.3 mm long |
3 Spikelets paired, or at least the second nonfunctional spikelet represented by a naked pedicel. |
15 Spikelets 1.0-1.3 mm long |
16 Nodes glabrous; blades 1.9-8 mm wide; panicle branches 2-6; upper florets 0.8-1.1 mm long |
16 Nodes pubescent; blades 10-24 mm wide; panicle branches 18-50; upper florets 1.1-1.3 mm long |
15 Spikelets 1.3-4.1 mm long. |
17 Margins of upper glumes and lower lemmas fimbriate, or ciliate with soft hairs 5 mm or more long. |
18 Culms to 70 cm long; upper glumes and lower lemmas broadly winged, the wing fimbriate; spikelets 2.4-3 mm wide |
18 Culms to 220 cm long; margins of upper glume and lower lemmas long- ciliate, wingless; spikelets 1.1-2.5 mm wide. |
19 Panicle branches 2-7; spikelets 2.3-4.0 mm long, 1.7-2.5 mm wide |
19 Panicle branches (4-) 10-30; spikelets 1.8-2.8 mm long, 1.1-1.5 mm wide |
17 Margins of upper glumes and lower lemmas glabrous or pubescent, but not winged, fimbriate, or long- ciliate. |
20 Upper florets olive to dark brown. |
21 Plants aquatic AND culms decumbent; lower glumes often present |
21 Plants either not aquatic OR if aquatic then with erect culms; lower glumes absent. |
22 Panicle branches 10-28 (occasionally more). |
23 Plants annual; axes of panicle branches broadly winged, the wings about as wide as the central portion; [common native] |
23 Plants perennial; axes of panicle branches narrowly winged, the wings narrower than the central portion; [rare exotics]. |
24 Blades 7-18 mm wide; axes of panicle branches 0.5-1.2 mm wide; spikelets 1.1-1.8 mm wide; upper florets 1.8-2.2 mm long |
24 Blades 10-30 mm wide; axes of panicle branches 1-1.7 mm wide; spikelets 1.8-2.4 mm wide; upper florets 2.5-2.7 mm long |
22 Panicle branches 1-10. |
25 Upper glumes glabrous. |
26 Blades to 15 mm wide; panicle branches 1-10 (-28); branch axes 0.7-2.3 mm wide; spikelets 2-2.2 mm long |
26 Blades to 7 mm wide; panicle branches 2-8; branch axes 0.6-1.1 mm wide; spikelets 2.2-3 mm long. |
27 Panicle branches 2-7, 1.6-7.1 cm long; spikelets 2.5-3 mm long, 1.5-2.2 mm wide; upper florets dark brown |
27 Panicle branches 5-8, 3.5-11 cm long; spikelets 2.2-2.7 mm long, 1-1.4 mm wide; upper florets chestnut brown |
25 Upper glumes pubescent. |
28 Rhizomes 5-25 cm long; ligule 1.2-1.5 mm long; panicle branches to 5.2 cm long; mature lower lemma transversely rugose |
28 Rhizomes indistinct or absent; ligule 1-4.1 mm long; panicle branches to 11 cm long; mature lower lemma not transversely rugose. |
29 Ligules 1-2 mm long; panicle branches 4-13, 6-11 cm long; spikelets 1.1-1.8 mm wide |
29 Ligules 2-4.1 mm long; panicle branches 1-7, 1.1-7.1 cm long; spikelets 1.5-2.4 mm wide. |
30 Plants annual; culms to 53 cm long; blades to 12 mm wide, flat; ligules 2-4.1 mm long; branch axes 0.8-1.3 mm wide; spikelets 2.1-2.6 mm long |
30 Plants perennial; culms to 110 cm long; blades to 5.4 mm wide, usually conduplicate; ligules 2-3 mm long; branch axes 0.6-1.1 mm wide; spikelets 2.5-3 mm long |
20 Upper florets white, stramineous, or golden brown. |
31 Panicle with 15-100 branches. |
32 Plants annual; ligules 0.1-0.3 mm long; blades to 13 cm long; panicle branches to 2.5 cm long; upper glumes and lower lemmas rugose |
32 Plants perennial; ligules 1-6.3 mm long; blades to 62 cm long; panicle branches to 13 cm long; upper glumes and lower lemmas smooth. |
33 Plants rhizomatous; nodes and sheaths glabrous; panicle branch axes 0.9-1.2 mm wide |
33 Plants cespitose; nodes and sheaths pubescent; panicle branch axes 0.3-0.6 mm wide. |
34 Culms to 400 cm long; blades 10-23 mm wide; panicle branches 5-13 cm long, spreading to reflexed; spikelets 1.8-1.9 mm wide |
34 Culms to 180 cm long; blades 4.9-6.1 mm wide; panicle branches 1.2-8.5 cm long, erect to ascending; spikelets 0.9-1.3 mm wide |
31 Panicles with 1-15 branches. |
35 Spikelets 1.3-2.5 mm long. |
36 Upper glumes and often lower lemmas shortly pubescent. |
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38 Panicles both terminal and axillary, the axillary panicles partially or completely enclosed by the subtending leaf sheath |
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36 Upper glumes and lower lemmas glabrous. |
39 Panicles both terminal and axillary, the axillary panicles partially or completely enclosed by the subtending leaf sheath |
39 Panicles all terminal. |
40 Ligules 0.2-0.4 mm long; branch axes 0.2-0.5 mm wide; spikelets 1.3-2 mm long, 0.7-1 mm wide |
40 Ligules 0.5-4.7 mm long; branch axes 0.3-2 mm wide; spikelets 1.6-3.1 mm long, 1-2.8 mm wide. |
41 Ligules 2.2-4.7 mm long; branch axes 1.5-2 mm wide, broadly winged |
41 Ligules 0.5-2.9 mm long; branch axes 0.4-2 mm wide, narrowly winged or wingless. |
42 Spikelets 2-2.8 mm wide, orbicular to suborbicular. |
43 Lower sheaths villous or hirsute; spikelets 2.6-3.5 mm long |
43 Lower sheaths glabrous or sparsely papillose- pubescent; spikelets 2.2-2.8 mm long |
42 Spikelets 1-1.9 mm wide, elliptic, ovate, or obovate. |
44 Spikelets 1.6-2.2 mm long, 1.1-1.3 mm wide |
44 Spikelets 2.1-3.7 mm long, 1-1.9 mm wide. |
45 Blades 0.2-2 (rarely -8) mm wide; panicle branch axes 0.5-1.2 mm wide; spikelets 2.3-3.7 mm long, 1.3-1.9 mm wide |
45 Blades 3-7 mm wide; panicle branch axes 0.3-0.8 mm wide; spikelets 2.2-2.5 mm long, 1-1.3 mm wide |
35 Spikelets 2.5-4.1 mm long. |
46 Spikelet pairs hardly imbricate, irregularly approximate, with evident gaps between groups of spikelets on the branches; lower glumes usually present; upper glumes (6-) 7-veined |
46 Spikelet pairs imbricate; lower glumes absent or present; upper glumes 1-5-veined. |
47 Upper glumes and lower lemmas pubescent (sparsely so, if at all, in P. pubiflorum). |
48 Panicle branches 1-4; branch axes 0.2-1 mm wide; spikelets 1.3-1.6 mm wide; lower glumes present |
48 Panicle branches 4-9; branch axes 1.1-2.3 mm wide; spikelets 1.5-2 mm wide; lower glumes absent. |
49 Blades 2-5 mm wide; branches ascending to erect; branch axes 1.2-1.5 mm wide; spikelets 2.8-3 mm long, 1.5-1.6 mm wide |
49 Blades 4-18 mm wide; branches ascending to spreading; branch axes 1.1-2.3 mm wide; spikelets 2.8-3.6 mm long, 1.5-2 mm wide. |
50 Blades becoming narrow basally; spikelets glabrous |
50 Blades rounded basally; spikelets pubescent |
47 Upper glumes and lower lemmas glabrous (sometimes sparsely pubescent in P. pubiflorum). |
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52 Plants aquatic; blades to 10 mm wide; panicle branches ascending to erect, to 12 cm long; spikelets 2.5-3 mm long, 1.3-1.6 mm wide; lower glumes often present; upper glumes and lower lemmas with 5 veins |
52 Plants terrestrial; blades to 18 mm wide; panicle branches ascending to spreading, to 7.9 cm long; spikelets 2.8-3.6 mm long, 1.5-2 mm wide; lower glumes absent; upper glumes and lower lemmas with 3 veins. |
53 Blades narrowing basally; spikelets glabrous |
53 Blades rounded basally; spikelets pubescent |
51 Plants rhizomatous (shortly so in Paspalum praecox). |
54 Blades 0.2-2 (-8) mm wide, involute; panicle branches 1-3; upper glumes 1-veined |
54 Blades 2.2-18 mm wide, flat to folded; panicle branches 1-10; upper glumes 3-5-veined. |
55 Ligules to 3.3 mm long; blades to 18 mm wide; spikelets 2.9-4.1 mm long; upper glumes 5-veined; upper florets golden brown |
55 Ligules to 2.2 mm long; blades to 8.3 mm wide; spikelets 2.1-3.1 mm long; upper glumes 3-veined; upper florets white, straminous, light yellow or golden brown. |
56 Blades 3-4 mm wide, flat; panicle branches 1-3, erect, 7-15 cm long; spikelets 2.7-3 mm long, 1.4-2 mm wide |
56 Blades 2.2-8.3 mm wide, folded to flat; panicle branches 2-10, ascending to spreading, 0.8-10.3 cm long; spikelets 2.1-3.1 mm long, 2-2.8 mm wide. |
57 Lower sheaths villous or hirsute; spikelets 2.6-3.5 mm long |
57 Lower sheaths glabrous or sparsely papillose- pubescent; spikelets 2.2-2.8 mm long |
