MANUAL OF THE GRASSES OF THE UNITED STATES 635 



Spikletes 2.7 to 4 mm. long, acuminate. 



First glume about one-third the length of the spikelet, subacute or blunt. 



137. P. STRAMINEUM. 



First glume usually more than half the length of the spikelet, acuminate. 



First glume more than three-fourths the length of the spikelet; spikelets 4 mm. long. 



136. P. PAMPINOSUM. 



First glume half to two-thirds the length of the spikelet; spikelets not more than 



3.3 mm. long 135. P. hirticaule. 



6. Diffusa 

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



139. P. CAPILLARIOIDES. 



Second glume and sterile lemma not elongate. 



Culms as much as 1 cm. thick; blades 2 cm. wide or more 144. P. hirsuttjm. 



Culms slender; blades not more than 1 cm. wide. 



Spikelets 4 to 4.2 mm. long; midnerves of glumes and sterile lemma scabrous toward 



the apex 142. P. lepidtjlum. 



Spikelets usually less than 3.5 mm. long. 



Blades hirsute on both surfaces (sometimes glabrescent), not at all glaucous. 



143. P. ghiesbreghtii. 



Blades glabrous on both surfaces or with a few hairs on either surface, glaucous above. 



Panicle much exceeding the leaves; spikelets 3 to 3.5 mm. long (rarely 3.7 mm.). 



141. P. HALLII. 



Panicle usually equaled or exceeded by the uppermost blades; spikelets 2 to 2.6 mm. 



long 140. P. filipes. 



7. Trichoidea 

 A single species 145. P. trichoides. 



8. Maxima 



Culms with a cormlike base - 148. P. bulbosum. 



Culms not cormlike at base. 



Nodes hirsute; ligules 4 to 6 mm. long; fruit strongly rugose 146. P. maximum. 



Nodes glabrous; ligules 2 mm. long; fruit obscurely rugose 147. P. plenum. 



9. Virgata 



Spikelets not more than 2.5 mm. long, first glume less than half the length of the spikelet. 

 Panicle loosely flowered; first glume truncate, about one-fifth the length of the spikelet. 



149. P. REPENS. 

 Panicle rather densely flowered ; first glume triangular, about one-third the length of the 



spikelet 150. P. gouini. 



Spikelets 3 to 7 mm. long (sometimes less than 3 mm. in P. virgatum var. cubense) ; first 

 glume more than half the length of the spikelet. 

 Panicle elongate, strongly contracted ; seacoast plants. 



Culms rarely 1 m. tall, solitary from the nodes of the horizontal rhizome. 



153. P. am arum. 



Culms 1 to 2 m. tall, in dense tufts 154. P. amarulum. 



Panicle diffuse, or only slightly contracted; plants sometimes of salt marshes but not 

 littoral. 

 Spikelets 6 to 8 mm. long; culms solitary, with a creeping base.... 152. P. havardii. 

 Spikelets less than 5 mm. long (in exceptional specimens 6 mm. long) ; culms erect, pro- 

 ducing numerous scaly rhizomes 151. P. virgatum. 



10. Tenera 



A single species 155. P. tenerum. 



11. Agrostoidea 



Rhizomes present; culms but little compressed; spikelets set obliquely on the appressed 

 pedicels. 

 Panicles open; spikelets 3.4 to 3.8 mm. long (shorter in exceptional specimens). 



162. P. ANCEPS. 

 Panicles more or less contracted; spikelets not more than 2.8 mm. long. 



163. P. RHIZOMATUM. 



Rhizomes wanting; culms strongly compressed with keeled sheaths; spikelets not obliquely 

 disposed (except in P. abscissum) . 



