270 BULLETIN 772, U. S. DEPARTMENT OF AGRICULTURE. 



The commonest species of the genus in the United States is Sor- 

 ghastrum nutans (L.) Nash (fig. 163), sometimes called Indian reed 

 or Indian grass. This is a tall, erect grass with handsome bronze- 

 colored panicles as much as a foot long, the awns about half an inch 

 long, the anthers brilliant yellow. The species is found in prairies 

 and open woods throughout the eastern United States and south- 

 westward to Arizona and Mexico. It is a common constituent of 

 prairie hay in the eastern part of the Great Plains region. 



Two other species are found in the Southern States, both with 

 awns about an inch long, Sorghaetrum elliottii (C. Mohr) Nash, with 

 pedicels villous only at the very tip, and S. secundum (Chapm.) Nash, 

 with a one-sided panicle and pedicels villous along the upper portion. 



135. RHAPHIS Lour. 



Spikelets in threes, one sessile and perfect, the other two pedicellate 

 and sterile, or sometimes a pair below, one fertile and one sterile; 

 fertile spikelet terete, the glumes coriaceous; sterile and fertile 

 lemmas thin and hyaline, the latter long-awned. 



Perennial grasses, or our species annual, with open panicles, the 

 three spikelets (reduced racemes) borne at the ends of long, slender, 

 naked branches. Species about 20, all in the tropical regions of the 

 Eastern Hemisphere except the 1 found in the southern United States. 



Type species: Rhaphis trivialis Lour. 



Rhaphis Lour., Fl. Cochinch. 553. 1790. Only one species described, which 

 is the same as Andropojion- (idculatus Retz. Some authors have thought the 

 name Rhaphis was invalidated by the earlier Rhapis L. f. (1789), a genus of 

 palms. The names have a different derivation and a different pronunciation, 

 and the one does not invalidate the other. 



Pollinia Spreng., Pugill. 2: 10, 1815, not Pollinia Trin., 1832. Type species, 

 P. gryllus Spreng. (Andropogon gryllus L. ). Several species are described, 

 but the generic characters are given under the first species. 



Centrophorum Trin., Fund. Agrost. 106, pi. 5. 1820; Type species, C. chincnse 

 Trin. (Andropoyon (iciculfttu* Retz.), the only one described. 



Chrysopogon Trin., Fund. Agrost. 187. 1820. Type species, Andropogon 

 gryllus L. Two species are mentioned, C. gryllus and C t aciculatus, but an 

 illustration of the first is cited. 



The only species occurring in the United States is Rhaphis pauci- 

 flora (Chapm.) Nash (fig. 164), an annual found in Florida and 

 Cuba. This has the aspect of a species of Stipa, the spikelets with 

 their long awns and barbed callus resembling the fruit of Stipa 

 spartea. The long slender branches of the few-flowered panicle bear 

 a terete, brown, sessile fertile spikelet and two slender sterile pedicels, 

 each with a slender glume. The peduncle disarticulates by a long 

 oblique line through the thickened villous end, the portion separating 

 with the spikelet being densely brown-villous, this forming a long 

 sharp callus. The glumes are coriaceous and at maturity separate 

 somewhat, the spikelet gaping at the apex. The palea is present, but 



