HITCHCOCK AND CHASE NORTH AMERICAN PANICUM, 



19 



The first glume in this genus is typically not more than half the length of the spikelet, 

 and is commonly much shorter than this, but in a few species, as in P. glatinosum 

 Swartz, P. urvilleanum Kunth, and in most of those included under "Miscellaneous 

 Species ' ' the first glume is nearly as long as the second . All the outlying species at the 

 end, nos. 192 to 196, depart in some particular from typical Panicum, such departure 

 being discussed under each species. 



KEY TO SPECIES AND GROUPS. 



Axis of branchlets extending beyond the base of the upper- 

 most spikelet as a point or bristle 1 to 6 mm. 

 long See subgenus 



Axis of branchlets not extending into a bristle. (In P. gemi- 

 natum and P. paludivagum the somewhat flattened axis 

 pointed but not bristle-form.) 

 Plants annual. 



Inflorescence consisting of several more or less secund 

 spike-like racemes. 

 Fruit smooth and shining; spikelets about 1.5 mm. 

 long. 

 Rachis bearing slender bristles (these wanting in 

 exceptional specimens); nodes usually villous. . 59. 



Rachis without bristles; nodes glabrous 60. 



Fruit transversely rugose; spikelets 2 mm. or more 

 long See 



Inflorescence a more or less diffuse panicle. 

 Spikelets tuberculate See 



Spikelets not tuberculate. 



Spikelets 1.2 to 1.4 mm. long; tropical species See 



Spikelets 1.7 mm. or more long. 



Glumes and sterile lemma hispid along the mar- 

 gins 76. 



Glumes and sterile lemma glabrous. 



First glume not over one-fourth the length of the 

 spikelet, truncate or triangular-tipped See 



First glume usually as much as one-half the 

 length of the spikelet, acute or acuminate. .See 



Plants perennial. 



Spikelets short-pediceled along one side of the rachises, 

 forming spike-like racemes. 

 First glume nearly equaling the sterile lemma. 



Racemes spreading; fruit not over one-third the 

 length of the spikelet 196. 



Paurochaetium , 

 , p. 22. 



P. pilosum. 

 P. laxum. 



Fasciculata, 

 p. 35. 



Verrucosa, 

 p. 126. 



TRICH O IDIA , 



p. 129. 



P. costaricense. 



DlCHOTOMIFLORA , 



p. 47. 



Capillaria, 

 p. 54. 



P. gymnocarpon . 



