108 Key to the System of 



528. Spikelets immersed into the notches of the rhachis of 



Spikelets arranged in compressed almost sessile spikes, 

 seated by alternate pairs in excavations of the rhachis, 

 one spikelet in each pair fertile and sessile, the other 

 sterile with adnate stalklet ; all bracts awnless and 

 smooth ; stamens three. Hemarthria. 2033 



Spikelets emersed ... ... ... ... 529 



529. Lowest bract longer than the next. 



Spikelets solitary on their stalklet, arranged in a raceme- 

 like spike; all bracts awnless; lowest bract keeled, smooth, 

 hardened ; stamens three. Zoysia. 2034 



Lowest bract shorter than the next ... ... ... 530 



530. Spikelets crowded into pungently foliaceous headlike- 



fascicular clusters. 



Staminate and pistillate flowers mainly on separate plants, 

 the staminate spikelets spicate, the pistillate spikelets 

 solitary and accompanied by one staminate or neuter 

 flower ; rhachis elongated, spinescent ; all bracts awn- 

 less ; fruit -supporting bract hardened. Spinif ex. 2035 



Spikelets arranged in a spike or panicle ... ... 531 



531. Spikelets surrounded by bristlets. 



Spikelets generally arranged in a spike-like almost cylin- 

 drical panicle, always small, jointed above the persistent 

 involucre ; all bracts awnless, smooth ; stamens three. 



Setaria. 2036 



Spikelets without any surrounding bristlets ... ... 532 



532. Lowest empty bract conspicuously awned. 



Spikelets arranged in somewhat paniculate and unilateral 



clusters, always small ; stamens three. OplismeilUS. 2037 



Lowest empty bract awnless ... ... ... ... 533 



533. The second of the two empty bracts about as large 



as the third, and usually somewhat exceeding the 

 firm fruit-supporting bract. 



Spikelets arranged in a panicle or in often unilateral spikes, 

 always small, those of some species (Isachne) producing 

 two fruits ; fruit-bearing flower accompanied by a 

 staminate or sterile flower ; stamens three. Panicum. 2038 



