62 PAXICACE^. 



linear, truncate, mucronate, 2-keeled, convex on the back, 3-nerved ; 

 third shorter, nerveless, fourth a little shorter, linear, entire or 

 with two short lobes, 1-nerved, the awn 12-15 cm. long, flexuose, 

 scabrid, stout, 10-15 cm. long; palea 0. Anthers 1.5 mm. long. 

 Pedicellate spikelets on scabrid pedicels as long as the sessile 

 spikelet, first glume subulate, 3-nerved. 



Florida, Chapmcm, Garher, Curtiss 3644*. 



Subgenus 7. Dichaxthium Hack. D. C. Monog. Phan. 6 : 566 

 (1889). DichantMum Willem, in Usteri Ann. Bot. 18 : 11 (1796). 



Eacemes digitate or rarely solitary, terminal or lateral, forming 

 a true panicle, the lower fourtli of the racemes homagamous. The 

 perfect spikelets obcompressed, awned; first glume keeled above, 

 second keeled, awnless, third hyaline, fourth very narrow, bearing 

 a short awn at the tip or between the teetli. Grain compressed, 

 flat in front, convex on the back; embryo a half to two-thirds the 

 length of the grain ; pedicellate spikelets staminate or rarely neuter. 



Perennials, excepting A. piptatherus, with flat leaf-blades. 

 Culms rarely branching; panicle more or less exserted, the ho- 

 mogamous part persistent, the rest deciduous. Found in tropical 

 regions. 



30. A. piptatherus Hack. Mart. Fl. Bras. 2 ; part 3,293 (1883). 



Yar. Palmeri Hack. D. C. Monog. Phan. 6 : 580 (1889). 



Annual; culms erect, slender, terete, 30-40 cm. high, most of 

 the bearded nodes bearing 1 or 2 compound branches. Sheaths 

 loose, compressed, thinly pilose; ligule short, obtuse; blades thin, 

 narrow at the base, 8-25 cm. long, 3-10 mm. wide, more or less 

 pubescent with tubercled hairs. Racemes usually corymbose, pedi- 

 cels very smooth, barbellate in the axils, 2.5-5 cm. long. Fertile 

 spikelets 4 mm. long, linear-oblong, first glume firm, obtuse mar- 

 gins involute, 5-7-nerved, pilose on the lower third or half; second 

 as long as the first, keeled, 3-nerved, glabrous; fourth bearing an 

 awn 2.5-3.5 cm. long. Anthers 0.5-1 mm. long. Pedicellate 

 spikelets neuter, consisting of two glumes. 



Mexico, Palmer 591, Pringle 4612. 



Subgenus 8. Heteropogon Hack. D. C. Monog. Phan. 6 : 

 583 (1889). Heteropogon (genus) Pers. Syn. 2 : 533 (1807). 



