110 NORTH AMERICAN FLORA [VoLUME 17 
filiform, or stouter and convex on the back, sometimes thickened at the apex, when separated 
with no deep depression nor appendage at the apex. Spikelets in pairs, dorsally compressed, 
the sessile one of the lower pair or pairs often differing from those above in sex, shape, or awns. 
Sessile spikelet, of at least the upper pairs, perfect, very rarely pistillate, usually awned; 
first scale commonly 2-keeled, with the margins infolded; second scale keeled; third scale 
hyaline; fourth scale usually hyaline, often parted or toothed at the apex and awned, more 
rarely entire and awnless, occasionally stipe-like, the awn perfect (with a spiral column) or 
imperfect. Pedicellate spikelet staminate or empty, as large as, or rarely larger than, the 
sessile one, often reduced to 1 or 2 scales, or entirely wanting, very rarely with a perfect flower. 
Stamens 1-3. Ovary glabrous. Stigmas from shorter to longer than the styles, usually 
exserted about the middle of the spikelet. 
Type species, Andropogon hirtus L. 
Raceme 1. 1. A. spathifiorus. 
Racemes 2 or more. 
Sessile spikelets of all pairs, even the lowest, in all the racemes, alike. 
Pedicellate spikelet empty, of ] or 2 scales, much smaller than the 
sessile spikelet, sometimes entirely wanting, or occasionally 
in A. bicornis large and staminate. 
Stamen 1. 
Sessile spikelet 5 mm. long or less, the awn imperfect, or some- 
times a little spiral at the base; pedicellate spikelet 
wanting or rudimentary, up to 2mm. long. 
Sessile spikelet with the intercarinal space of the first scale 
nerveless ; anthers small, less than 2 mm. long. 
Racemes of 8-20 internodes. 
Inflorescence oblong to oval or obovate, the branches 
many times divided, the lower ones often elon- 
gate, forming 1 or more corymbiform masses ; 
upper leaf-blades usually equaling or exceeding 
the inflorescence. 
Spathes rough; apex of the common peduncle of 
the racemes hispidulous below the barbed sum- 
mit. 2. A. glomeratus. 
Spathes smooth; apex of the common peduncle 
glabrous below the barbed summit. 3. A. tenuispatheus. 
Inflorescence long and narrow, linear, the branches 
not forming corymbiform masses. 
Sheaths not enlarged. 
Racemes long and lax, the internodes of the 
rachis much exceeding the sessile spikelets. 15. A. campyloracheus. 
Racemes relatively short and stout, the inter- 
nodes equaling or shorter than the sessile 
spikelets. 
Racemes sessile or nearly so, the common 
peduncle not more than 5 mm. long. 
Plant green; leaf-sheaths and blades, 
either or both, pubescent. 
Pubescence on the leaves dark, lax 
and spreading ; pedicels and rachis- 
internodes relatively sparsely long- 
hairy above, usually naked below ; 
callus-hairs less than one half as 
long as the spikelet. 4. A, virginicus. 
Pubescence on the leaves appressed, 
long and silky ; pedicels and rachis- 
internodes ‘copiously long-hairy 
their entire length; callus-hairs 
more than one half as long as the 
spikelet. 5. A. longiberbis. 
Plant blue- or gray-green, intensely glau- 
cous; leaves glabrous. 6. A. capillipes. 
Racemes never sessile, the common pedun- 
cle more than 5 mm. long, usually more 
than 1 cm. or sometimes entirely ex- 
serted from the apex of the spathe. 
Racemes in pairs. 
Ligule rounded or acutish at the apex, 
1-1.5 mm. long ; blades of the innova- 
tions laterally compressed, the surface 
grown together, leaving a groove or 
furrow on the upper side. 7. A. perangustatus. 
Ligule a short, scarious, often ciliate, 
ring of equal length, less than 1 
