26 



IscH^aitrM, Linn. 



Spikelets in pairs in the alternate notches of the articulate 

 flexuous rhachis of simple spikes, one sessile with one perfect flower 

 and a male one below it, the other pedicelled and similar or defec- 

 tive. The sessile spikelet has two thickish outer glumes and two 

 thin hyaline flowering glumes, the upper one usually awned. The 

 palea are small and hyaline, sometimes absent. 

 1. I. leersioides, Jfuaro. Introduced in California. 



Heteropogon, Pers. 



Spikelets one-flowered, monoecious, in pairs in the notches of the 

 rhachis of a one-sided spike, one sessile and pistillate, cylindrical, 

 turned to one side of the spike, the other pedicelled and staminate, 

 imbricate on the other side of the spike. The lower outer glume is 

 hard and convolute ; the upper, thinner and keeled ; the third glume 

 is thin and hyaline ; the fourth, or flowering glume, terminated with 

 a hard, twisted awn ; palets very small and thin or wanting. 



1. H. contortus, B. cfi S. (Andropogon contortus, Z.) Texas and 



Southwest. 



2. H. contortus, var. glaber. Hackel. (H. Allioni, JR. tfc S.) West 



Texas to Arizona. 



3. H. acuminatus, Trin. (Andropogon melanocarpus, Chap.) South 



Carolina to Florida. 



Trachypogon, JTees. 



Spikelets arranged and constituted as in Heteropogon, except that 

 the sessile spikelet is male and the pedicelled one pistillate. 

 1- T. polymorphus, Hack., var. Montufari, Hack. (T. Montufari, 

 Nees.) West Texas to Arizona. 



Andropogon, Linn. 



Inflorescence in simple or paniculate spikes. Spikelets in pairs in 

 the alternate notches of the rhachis, one sessile and fertile, the other 

 pedicelled and sterile, (either male or empty.) Fertile spikelet with 

 two more or less coriaceous outer glumes, a third hyaline empty 

 glume, and the fourth or flowering glume also hyaline and awned. 

 The sterile spikelet similar, but empty or male only and nnawned. 

 Palet small and hyaline or wanting. 



