610 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



Culms slender; blades not more than 6 mm wide; spikelets not turgid. 



Axillary pulvini pilose 123. P. philadelphictjm. 



Axillary pulvini glabrous 124. P. tuckermani. 



Spikelets 2.7 to 4 mm long, acuminate. 



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



blunt 129. 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 128. P. pampinosum. 



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

 more than 3.3 mm long 127. P. hirticaule. 



6. Diffusa 



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



fruit 131. P. CAPILLARIOIDES. 



Second glume and sterile lemma not elongate. 



Culms as much as 1 cm thick; blades 2 cm wide or more_ _ 136. P. hirsutum. 

 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 134. P. lepidulum. 



Spikelets usually less than 3.5 mm long. 



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



glaucous 135. 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) 133. P. hallii. 



Panicle usually equaled or exceeded by the uppermost blades; spikelets 

 2 to 2.6 mm long 132. P. filipes. 



7. Maxima 



Culms with a cormlike base 139. P. bulbosum. 



Culms not cormlike at base. 



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



137. P. MAXIMUM. 



Nodes glabrous; ligules 2 mm long; fruit obscurely rugose. . 138. P. plenum. 



8. 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 140. P. repens. 



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



length of the spikelet 141. 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 rhi- 

 zome 144. P. AMARUM. 



Culms 1 to 2 m tall, in dense tufts 145. 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. 



143. P. HAVARDII. 



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

 erect, producing numerous scaly rhizomes 142. P. virgatum. 



9. Tenera 



A single species 146. P. tenerum. 



10. 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). 



152. P. ANCEPS. 



