HITCHCOCK—MEXICAN GRASSES. 241 
35. PANICUM L. Sp. Pl. 55. 1753. 
KEY TO THE SPECIES. 
Axis of branchlets extending as a bristle beyond the base 
of the uppermost spikelet.................--..-... 1. P. ramisetum. 
Axis of branchlets not extending into a bristle. 
Plants annual. 
Inflorescence consisting of several more or less 
secund spike-like racemes. 
Spikelets 5 to 6 mm, long..............-.... 9. P. texanum. 
Spikelets 2 to 4 mm. long. 
Spikelets strongly reticulate-veined, gla- 
brous. 
Panicle branches long and spread- 
ING... eee eee eee eee eee 6. P. fasciculatum. 
Panicle branches short, appressed... 6a. P. fasciculatum charta- 
ginense. 
Spikelets scarcely reticulate-veined, or 
near apex only. 
Spikelets not over 2 mm. long, gla- 
brous ..........-..-...-..--- 5. P. reptans. 
Spikelets over 3 mm. long, pubes- 
cent. 
Plants velvety; sheaths not pap- 
illose.......--22------- 7. P. molle. 
Plants not velvety; sheaths pap- 
illose .......2-....222-- 8. P. arizonicum. 
Inflorescence a more or less diffuse panicle. 
Spikelets 1.2 to 1.4 mm. long, pubescent; 
blades more than one-fourth as wide as 
long... --- eee scene cece cece eee ee eee 39. P. trichoides, 
Spikelets 1.7 mm. or more long, glabrous. 
First glume not over one-fourth the 
length of the spikelet, blunt or 
triangular-tipped; spikelets on 
short appressed pedicels........ 10. P. vaseyanum. 
First glume usually as much as half the 
length of the spikelet, acute, or 
acuminate; spikelets on slender, 
usually spreading pedicels. 
Panicles more or less drooping...... 15. P. sonorum. 
Panicles erect. 
First glume about one-third the 
length of the spikelet, 
subacute or blunt....... 14. P. stramineum. 
First glume more than half the 
length of the spikelet, 
acuminate. 
Spikelets 4.5 to 6 mm. long. 
Spikelets 6 mm. long, 
scattered........ 16. P. parcum. 
Spikelets scarcely over 
5 mm. long, ap- 
proximate...... 13. P. decolorans. 
