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. glutinosum 
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. 
C0) wee eee cece eee See subgenus PAUROCHAETIUM, 
p. 22. 
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. P. pilosum. 
Rachis without bristles; nodes glabrous. ........... 60. P.laxum, 
Fruit transversely rugose; spikelets 2 mm. or more 
long .. 2.2.2. See Fascicunata, 
p. 35. 
Inflorescence a more or less diffuse panicle. 
Spikelets tuberculate...........2..0..0.00.22222.2.. See VERRUCOSA, 
p. 126. 
Spikelets not tuberculate. 
Spikelets 1.2 to 1.4 mm, long; tropical species......See TRICHOIDIA , 
p. 129. 
Spikelets 1.7 mm. or more long. 
Glumes and sterile lemma hispid along the mar- 
GINS... eee eee .. 76. P. costaricense. 
Glumes and sterile lemma glabrous. 
First glume not over one-fourth the length of the 
spikelet, truncate or triangular-tipped.....See D1rcnoroMIrLoRA 
p. 47. 
oJ 
First glume usually as much as one-half the 
length of the spikelet, acute or acuminate..See CAPILLARIA, 
p. 54. 
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.............222.22.2..... 196. P. gymnocarpon. 
