MANUAL OF THE GRASSES OF THE UNITED STATES 727 



2a. Inflorescence very decompound, the profuse pairs of racemes aggregate in 

 an elongate or corymbose mass; spathes rarely more than 2 mm wide; 

 pedicellate spikelet obsolete (see also A. virginicus var. hirsutior.) 



24. A. GLOMERATUS. 



2b. Inflorescence not conspicuously decompound nor dense (rather dense in 

 A. virginicus var. hirsutior). 

 3a. Peduncle not more than 1 cm long, the dilated spathes exceeding the 2 

 (occasionally 3 or 4) racemes. 

 Upper sheaths inflated spathelike, aggregate, the late inflorescence a 



flabellate tuft 25. A. elliottii. 



Upper sheaths not inflated and aggregate. 



Blades of the innovations subfiliform; ligule acute, protruding from the 



folded blade; foliage usually glabrous 20. A. perangustatus. 



Blades 2 to 5 mm wide; ligule minute, concealed within the folded blade; 

 foliage from obscurely to conspicuously pubescent. 



Hairs of the racemes copious 19. A. longiberbis. 



Hairs of the racemes comparatively sparse. 



Rachis joints shorter than the spikelets 22. A. capillipes. 



Rachis joints as long as the spikelets 23. A. virginicus. 



3b. Peduncles 2 cm long or more. 



4a. Peduncles not more than 5 cm long, enclosed in the spat he or only 

 slightly exserted (see also A. -perangustatus) . 

 Racemes usually not more than 15 mm long; ultimate branchlets capil- 

 lary, spreading or recurved, long-villous at summit. 



21. A. BRACHYSTACHYS. 



Racemes 2 to 5 cm long. 



Racemes 4 to 6 to a peduncle, tawny; sheaths villous. _ 13. A. mohrii. 

 Racemes 2 to a peduncle, silvery or creamy white; sheaths glabrous 

 or nearly so. 

 Pairs of racemes numerous; spathes inconspicuous, at least some of 



the peduncles as much as 5 cm long 17. A. floridanus. 



Pairs of racemes not more than 10 to a culm; spathes dilated; 



peduncles 1 to 3 cm long 18. A. tracyi. 



4b. Peduncles or most of them 5 to 15 cm long, long-exserted (short- 

 exserted peduncles intermixed with long in A. elliottii and A. subtenuis). 

 Rachis joints longer than the spikelets; racemes 5 to 10 cm long, con- 

 spicuously slender and flexuous 27. A. campyloracheus. 



Rachis joints not longer than the spikelets; racemes not more than 7 cm 

 long, usually not more than 5 cm. 

 Upper sheaths inflated, overlapping, conspicuous. 25. A. elliottii. 

 Upper sheaths not inflated, overlapping, nor conspicuous. 



Spikelets 4 mm long; racemes very flexuous, the rachis joints 



nearly as long as the spikelets 26. A. subtenuis. 



Spikelets 5 to 7 mm long; racemes slightly or not at all flexuous, the 

 rachis joints distinctly shorter than the spikelets. 

 Sessile spikelets about 5 mm long, about 0.5 mm wide, the glume 

 deeply grooved; hairs of racemes not obscuring the spikelets. 



16. A. ARCTATUS. 



Sessile spikelets somewhat more than 5 mm long, 1 to 1.5 mm 



wide, the glume concave but not grooved; hairs of racemes 



conspicuous to copious. 



Racemes copiously long-villous, the hairs about twice as long 



as the spikelet and obscuring it; first glume of sessile 



spikelet nerveless and glabrous between the keels. 



15. A. TERNARIUS. 



Racemes not copiously villous, the hairs about as long as the 

 spikelet, not obscuring it; first glume of sessile spikelet 

 scabrous and often 2-nerved between the keels. 



14. A. CABANISII. 



Section 3. Amphilophis 



Racemes 3 to 7, not conspicuously woolly; pedicellate spikelet about as large as 



the sessile one. Sessile spikelet often pitted 28. A. wrightii. 



Racemes few to many, conspicuously woolly; pedicellate spikelet reduced. 



Panicle subflabellate, often short-exserted or included at base in a dilated sheath; 

 racemes few to many on a relatively short axis; spikelets 5 to 6 mm long. 



30. A. BARBINODIS. 



