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



scarcely wider than their sheaths; spikelets about 2.3 mm. long, borne toward 



the ends of the few slender branches 12. Laxa. 



Sterile palea, if present, not enlarged. 



Plants with conspicuous creeping scaly rhizomes. 



Spikelets long-pediceled, not secund, arranged in an open or contracted 



panicle 9. Virgata. 



Spikelets short-pediceled, more or less secund along the nearly simple panicle 



branches 11. Agrostoidia. 



Plants without creeping scaly rhizomes. 



Panicles narrow and few-flowered; culms erect and wiry; blades drying in- 

 volute 10. Texera. 



Panicles open or contracted, many-flowered. 



Spikelets short-pediceled along the nearly simple panicle branches. 



11. Agrostoidia. 

 Spikelets long-pediceled, the panicle open 6. Diffusa. 



1. Geminata 



Spikelets 3 mm. long; glumes and sterile lemma papery 117. P. palttdivagum. 



Spikelets not more than 2.4 mm. long; glumes and sterile lemma not papery. 



116. P. GEMINATUM. 



2. Purpurascentia 

 A single species 118. P. purpurascens. 



3. Fasciculata 



Spikelets 5 to 6 mm. long 124. P. texanum. 



Spikelets 2 to 4 mm. long. 



Spikelets strongly reticulate-veined, 2 to 3 mm. long, glabrous.... 120. P. fasciculatum. 

 Spikelets scarcely reticulate-veined or only near apex. 



Spikelets not more than 2 mm. long, glabrous 119. P. reptans. 



Spikelets more than 3 mm. long, pubescent. 



Rachis scabrous but not bristly; spikelets acuminate-pointed, 4 to 4.5 mm. long. 



121. P. ADSPERSTJM. 



Rachis and/or pedicels bristly-hirsute; spikelets acute, pubescent, or sometimes 

 glabrous, 3 to 4 mm. long. 

 Rachis and pedicels bristly-hirsute; blades lanceolate, rarely more than 7 mm. wide. 



123. P. ARIZOXICUM. 



Rachis scabrous, only the pedicels bristly-hirsute; blades ovate-lanceolate, as much 



as 2 cm. wide 122. P. ramosum. 



Dichotomiflora 



Plants perennial; blades elongate, 2 to 3 mm. wide 127. P. lacustre. 



Plants annual; blades mostly 5 to 15 mm. wide. 



Sheaths glabrous 125. P. dichotomiflorum. 



Sheaths papillose 126. P. bartowense. 



5. Capillaria 



Panicles drooping; spikelets 4.5 to 5 mm. long- 138. P. miliaceum. 



Panicles erect; spikelets not more than 4 mm. long. 

 Panicles more than half the length of the entire plant. 



Panicles narrow, usually less than half as broad as long 128. P. flexile. 



Panicles as broad as long. 



Fruit without scar at base 133. P. -capillare. 



Fruit with a lunate scar at base 134. P. hillmani. 



Panicles not more than one-third the entire height of the plant. 



Spikelets not more than 2.2 mm. long, acute but not long-acuminate (see also P. hir- 

 sutum). 

 Culms relatively stout; blades about 1 cm. wide; spikelets turgid. 



129. P. GATTINGERI. 



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

 Spikelets 1.7 mm. long; foliage green. 



Axillary pulvini pilose 130. P. philadelphicum. 



Axillary pulvini glabrous 132. P. tuckermani. 



Spikelets 2.1 to 2.2 mm. long; foliage conspicuously tinged with purple, the blades 

 erect 131. P. lithophilum. 



