Part 3, 1915] 



POACBAK 



203 



Spikelets 2.7-6 mm. long, acuminate. 



First glume usually more than half the length of the spike - 

 let, acuminate. 

 Spikelets not more than 4 mm. long. 



First glume half to two thirds the length of the 



spikelet; spikelets not more than 3.3 mm. long. 

 First glume more than three fourths the length of 

 the spikelet; spikelets 4 mm. long. 

 Spikelets 4.5-6 mm. long. 



Spikelets scarcely more than 5 mm. long, approxi- 

 mate. 

 Spikelets 6 mm. long, scattered. 

 First glume about one third the length of the spikelet, 

 subacute or blunt. 

 Inflorescence elongate, composed of several approximate implicate 

 t panicles. 

 Panicles more or less drooping. 



Spikelets not more than 3.5 mm. long; Mexican species. 

 Spikelets 4.5-5 mm. long; species introduced from the Old World. 



26. P. hirticaule. 



27. P. pampinosum 



28. P. decolor ans. 



31. P. par cum. 



29. P. stramineum 

 33. P. cayennense. 



30. P. sonorum. 



32. P. miliaceum. 



VI. Diffusa. 



Second glume and sterile lemma elongate, at least three times as long as 

 the fruit. 



Second glume and sterile lemma not elongate. 



Culms slender, less than 1 meter tall; leaf -blades not more than 1 cm, 

 wide. 

 Blades 1—3 mm. wide; plants spreading or ascending. 

 Blades mostly more than 5 mm. wide; plants erect. 

 Spikelets usually less than 3.5 mm. long. 



Leaf -blades glabrous on both surfaces or with a few hairs 

 on either surface, glaucous above. 

 Panicles usually equaled or exceeded by the uppermost 



blades; spikelets 2-2.6 mm. long. 

 Panicles much exceeding the leaves; spikelets 3—3.5 mm. 

 (rarely 3.7 mm.) long. 

 Leaf -blades hirsute on both surfaces (sometimes glabre- 

 scent), not at all glaucous. 

 Spikelets 4—4.2 mm. long, the midnerves of glumes and sterile 

 lemma scabrous toward the apex. 

 Culms stout, usually more than 1 meter tall; leaf -blades 2 cm. or 

 more wide. 



VII. Maxima. 



Culms from a creeping rootstock, not corm-like at base. 



Nodes hirsute; ligules 4—6 mm. long; fruit strongly rugose. 



Nodes glabrous; ligules 2 mm. long; fruit very obscurely rugose. 

 Culms with a conn-like base. 



VIII. Virgata. 



Spikelets not more than 2.5 mm. long; first glume less than half the 

 length of the spikelet. 

 Panicles loosely flowered; first glume truncate, about one fifth the 



length of the spikelet. 

 Panicles rather densely flowered; first glume triangular, about one 



third the length of the spikelet. 

 Spikelets 3-7 mm. long (sometimes less than 3 mm. in P. virgaium 

 cubense) ; first glume more than half the length of the spikelet. 

 Panicles diffuse, or only slightly contracted ; plants sometimes of salt 

 marshes but not littoral. 

 Spikelets less than 5 mm. long (in exceptional specimens 6 mm. long) ; 

 culms erect, usually producing numerous scaly rhizomes. 

 Culms erect at base, slender, not more than 2 mm. in diameter; 

 ligules 2-4 mm. long. 

 Rhizomes present; panicle broader, the branches usually 



spreading or drooping. 

 Rhizomes absent; panicle narrow, one fourth to one third 

 as long as wide, the branches ascending. 

 Culms decumbent at base, as much as 6 mm. in diameter, 

 glaucous, 2-A: meters tall; ligules less than 1 mm. long. 

 Spikelets 6-8 mm. long; culms solitary, with a creeping base. 



elongate, strongly contracted; seacoast plants. 

 Culms rarely 1 meter tall, solitary from the nodes of the horizontal 



rhizome. 

 Culms 1-2 meters tall, in dense tufts. 



IX. Tenera. 



Panicle 3-8 cm. long; spikelets 2.2-2.8 mm. long, pointed. 



Panicle not more than 2 cm. long; spikelets 1.5-2 mm. long, not pointed. 



34. P. capillarioides. 



35. P. diffusum. 



36. P.filipes. 



37. P. Hallii. 



39. P. Ghiesbreghtii, 



38. P. lepidulum. 



40. P. hirsutum. 



41. P. maximum 



42. P. plenum. 



43. P. bulbosum. 



44. P. repens. 



45. P. Gouini, 



46. P. virgaium. 



47. P. icknanthoides 



48. P. altum. 



49. P. Havardii. 



50. P. amarum. 



51. P. amarulum. 



52. P. tenerum 



