1. Spikelets solitary, not associated with a naked pedicel or rudimentary spikelets. | → 2 |
2. Panicles with 1-70 branches, if more than 1, the branches racemosely arranged. | → 3 |
3. Branches 7-70, disarticulating at maturity, the axes extending beyond the distal spikelets | P. repens |
3. Branches 1-6, persistent, terminating in a spikelet. | → 4 |
4. Upper florets olive to dark brown | P. scrobiculatum |
4. Upper florets pale to stramineous. | → 5 |
5. Axes of panicle branches 0.6-1.3 mm wide | P. laeve |
5. Axes of panicle branches 1.8-3.3 mm wide. | → 6 |
6. Spikelets 1.7-2.1 mm long; upper lemmas glabrous throughout | P. dissectum |
6. Spikelets 3.2-4 mm long; upper lemmas with a few short hairs at the apices | P. acuminatum |
2. Panicles usually composed of a terminal pair of branches, sometimes with 1(-5) additional branches below the terminal pair. | → 7 |
7. Upper glumes pilose on the margins or shortly pubescent on the back. | → 8 |
8. Spikelets 1.3-1.9 mm long; upper glumes pilose along the margins | P. conjugatum |
8. Spikelets 2.4-3.2 mm long; upper glumes sparsely short pubescent on the back | P. distichum |
7. Upper glumes glabrous. | → 9 |
9. Spikelets elliptic, their apices acute to acuminate. | → 10 |
10. Plants rhizomatous, not appearing cespitose; usually in brackish to salt marsh habitats | P. vaginatum |
10. Plants shortly rhizomatous but appearing cespitose; usually in disturbed inland habitats | P. almum |
9. Spikelets ovate to broadly elliptic, their apices obtuse to broadly acute. | → 11 |
11. Spikelets 2.5-4 mm long; leaf blades flat or conduplicate | P. notatum |
11. Spikelets 1.9-2.3 mm long; leaf blades flat | P. minus |
1. Spikelets paired, if only 1 spikelet functional, a naked pedicel or rudimentary, non-functional spikelet present. | → 12 |
12. Spikelets 1-1.3 mm long. | → 13 |
13. Panicle branches 2-6; spikelets elliptic to elliptic-obovate, appressed to the branch axes | P. blodgettii |
13. Panicle branches 18-50; spikelets ovate, diverging from the branch axes | P. paniculatum |
12. Spikelets 1.3-4.1 mm long. | → 14 |
14. Margins of upper glumes and lower lemmas ciliate-lacerate and winged or pilose. | → 15 |
15. Upper glumes and lower lemmas ciliate-lacerate, winged | P. fimbriatum |
15. Upper glumes and lower lemmas pilose. | → 16 |
16. Panicle branches 2-7; spikelets 2.3-4 mm long | P. dilatatum |
16. Panicle branches (4)10-30; spikelets 1.8-2.8 mm long | P. urvillei |
14. Margins of upper glumes and lower lemmas neither ciliate-laceerate nor winged, glabrous or pubescent, if pubescent then the hairs not pilose, often glandular, papillose-based, or wrinkled. | → 17 |
17. Upper florets olive to dark brown. | → 18 |
18. Plants aquatic, the culms decumbent, rooting at the nodes; lower glumes often present | P. modestum |
18. Plants not aquatic or, if aquatic, the culms erect; lower glumes absent. | → 19 |
19. Panicle branches 10-28 or more. | → 20 |
20. Plants annual; axes of panicle branches broadly winged, wings about as wide as the central portion | P. boscianum |
20. Plant perennial; axes of panicle branches narrowly winged, wings narrower than the central portion. | → 21 |
21. Axes of panicle branches 1-1.7 mm wide; spikelets 1.8-2.4 mm wide | P. virgatum |
21. Axes of panicle branches 0.5-1.2 mm wide; spikelets 1.1-1.8 mm wide | P. conspersum |
| → 22 |
| → 23 |
23. Spikelets 1.3-1.8 mm wide, broadly elliptical to orbicular, glabrous; panicles with 1-10(28) branches, the axes 0.7-2.3 mm wide | P. boscianum |
23. Spikelets 1.7-2.4 mm wide, broadly obovate, shortly pubescent; panicles with 1-5 branches, the axes 0.8-1.3 mm wide | P. convexum |
| → 24 |
24. Plants cespitose, rhizomes sometimes present but not well-developed; culms 100-200 cm tall, stout; panicle branches ascending, divaricate, or reflexed. | → 25 |
25. Leaf blades 7-18 mm wide | P. conspersum |
25. Leaf blades 2.5-4 mm wide | P. plicatulum |
24. Plants not cespitose, rhizomatous; culms 10-150 cm tall, varying in thickness; panicle branches ascending. | → 26 |
26. Rhizomes short, indistinct | P. plicatulum |
26. Rhizomes long, evident. | → 27 |
27. Plants aquatic; upper florets chestnut brown | P. wrightii |
27. Plants not aquatic; upper florets dark brown | P. nicorae |
17. Upper florets white, stramineous, or golden brown. | → 28 |
28. Lower lemmas with well-developed ribs over the veins; upper glumes absent | P. malacophyllum |
28. Lower lemmas not ribbed over the veins; upper glumes present. | → 29 |
29. Panicles with 15-100 branches. | → 30 |
30. Plants annual; upper glumes and lower lemmas rugose | P. racemosum |
30. Plants perennial; upper glumes and lower lemmas smooth. | → 31 |
31. Plants rhizomatous, not cespitose; branch axes 0.9-1.2 mm wide; panicle branches often arcuate | P. intermedium |
31. Plants cespitose, not rhizomatous; branch axes 0.3-0.6 mm wide; panicle branches straight. | → 32 |
32. Panicle branches spreading to reflexed (rarely ascending); leaf blades 10-23 mm wide; axes of panicle branches 0.3-0.4 mm wide | P. coryphaeum |
32. Panicle branches erect to ascending; leaf blades 4.9-6.1 mm wide; axes of panicle branches 0.5-0.6 mm wide | P. quadrifarium |
29. Panicles with 1-15 branches. | → 33 |
33. Spikelet pairs not imbricate; lower glumes usually present | P. bifidum |
33. Spikelet pairs imbricate; lower glumes absent or present. | → 34 |
34. Spikelets 1.3-2.5 mm long. | → 35 |
35. Upper glumes, usually also the lower lemmas, shortly pubescent. | → 36 |
| P. langei |
| → 37 |
37. Panicles both terminal and axillary, the axillary panicles partially or completely enclosed by the subtending leaf sheath | P. setaceum |
37. Panicles all terminal. | → 38 |
38. Leaf blades involute; culms 80-110 cm tall | P. laxum |
38. Leaf blades flat; culms 20-75 cm tall. | → 39 |
39. Spikelets 1.3-2 mm long, 0.7-1 mm wide, elliptic; upper glumes and lower lemmas 5-veined; culm bases swollen | P. caespitosum |
39. Spikelets 2-2.5 mm long, 1.4-1.6 mm wide, ovate; upper glumes and lower lemmas 3-veined; culm bases not swollen | P. virletii |
35. Upper glumes and lower lemmas glabrous. | → 40 |
40. Panicles both terminal and axillary, the axillary panicles partially or completely enclosed by the subtending leaf sheath | P. setaceum |
40. Panicles all terminal. | → 41 |
41. Upper panicle branches erect | P. monostachyum |
41. Upper panicle branches spreading to ascending. | → 42 |
42. Leaf blades mostly involute; plants of sandy or rocky areas, usually on the coast | P. pleostachyum |
42. Leaf blades mostly flat; plants of inland areas or, if coastal, then in marshy areas. | → 43 |
43. Upper glumes and lower lemmas 3-veined. | → 44 |
44. Leaf blades usually conduplicate, 2.2-8.3 mm wide | P. praecox |
44. Leaf blades usually flat, 5-10 mm wide | P. virletii |
43. Upper glumes and lower lemmas 5-veined. | → 45 |
45. Axes of panicle branches 0.2-0.5 mm wide; ligules 0.2-0.4 mm long | P. caespitosum |
45. Axes of panicle branches 1.5-2 mm wide; ligules 2.2-4.7 mm long | P. lividum |
34. Spikelets 2.5-4.1 mm long. | → 46 |
46. Upper glumes, and usually lower lemmas, pubescent. | → 47 |
| P. langei |
| → 48 |
48. Leaf blades 2-5 mm wide; upper glumes and lower lemmas abundantly pubescent, most hairs longer than 0.1 mm; spikelets elliptic | P. bartwegianum |
48. Leaf blades 4-18 mm wide; upper glumes and lower lemmas glabrous or sparsely pubescent, the hairs shorter than 0.1 mm; spikelets obovate to elliptic | P. pubiflorum |
46. Upper glumes, and usually lower lemmas, glabrous. | → 49 |
49. Upper florets golden brown. | → 50 |
50. Plants not rhizomatous; culms decumbent and rooting at the lower nodes; spikelets 1.3-1.6 mm wide; lower lemmas 5-7-veined; lower glumes often present | P. modestum |
50. Plants rhizomatous; culms erect, not rooting at the lower nodes; spikelets 1.9-3.1 mm wide; lower lemmas 3-veined. | → 51 |
51. Panicle branches 1-6; upper glumes 5-veined; leaf blades 3-18 mm wide | P. floridanum |
51. Panicle branches 1-3; upper glumes 3-veined; leaf blades 3-4 mm wide | P. unispicatum |
49. Upper florets stramineous to pale, but not golden brown. | → 52 |
52. Terminal panicle branches erect. | → 53 |
53. Blades involute; upper glumes 1-veined | P. monostachyum |
53. Blades flat; upper glumes 3-veined | P. unispicatum |
52. Terminal panicle branches spreading to ascending. | → 54 |
54. Spikelets 2.2-2.6 mm long. | → 55 |
55. Spikelets 1.2-1.5 mm wide, elliptic to obovate | P. lividum |
55. Spikelets 2-2.8 mm wide, orbicular to suborbicular | P. praecox |
54. Spikelets 2.6-4.1 mm long. | → 56 |
56. Plants decumbent, rooting at the lower nodes, not rhizomatous; spikelets obovate to elliptic | P. pubiflorum |
56. Plants rhizomatous, neither decumbent nor rooting at the lower nodes; spikelets orbicular to elliptic. | → 57 |
57. Spikelets 2.1-3.1 mm long, 2-2.8 mm wide, orbicular to suborbicular; upper glumes 3-veined; leaf blades conduplicate | P. praecox |
57. Spikelets 2.9-4.1 mm long, 1.9-3.1 mm wide, suborbicular to elliptic; upper glumes 5-veined; leaf blades flat | P. floridanum |