Graminaceae 4] 
E. Lemma with a tuft of hair at base as long as the lemma. 
MUHLENBERGIA (p. 43) 
EE. Lemma without a tuft of hair at base. POLYPOGON (p. 43) 
DD. Lemma awnless or with a dorsal awn. 
F. Lemma with a tuft of hair at base. CALAMAGROSTIS (p. 45) 
FF. Lemma without a tuft of hair at base, though often ciliate on the keel. 
G. Glumes not conspicuously compressed-keeled; inflorescence distinctly 
lobed and raceme-like. AGROSTIS (p. 47) 
GG. Glumes conspicuously compressed-keeled; inflorescence a dense 
terete spike not or hardly lobed. 
H. Lemma with a dorsal awn 2—16 mm. long; glumes united for 
Y4—lV, their length at base. ALOPECURUS (p. 47) 
HH. Lemma awnless; glumes not united. PHLEUM (p. 49) 
BB. Inflorescence either plainly a panicle or if spike-like the spikelets distant and 
thus the spike not dense. 
I. Lemma with a terminal awn 0.3—20 cm. long; glumes sometimes awned. 
J. Lemma of fertile flower thin, membranous. MUHLENBERGIA (p. 43) 
JJ. Lemma of fertile flower firm, hardened. 
K. Lemma-awn 3-branched. ARISTIDA (p. 41) 
KK. Lemma-awn not branched. 
L. Lemma-awn twisted, persistent. STIPA (p. 42) 
LL. Lemma-awn not twisted, deciduous. Oryzopsis (p. 42) 
II. Lemma awnless or with a dorsal awn 1.2 cm. or less long; glumes awnless. 
M. Lemma with a tuft of hair at base. 
N. Glumes with awns 2—5 mm. long, about equal; lemma 3-veined. 
MUHLENBERGIA (p. 43) 
NN. Glumes awnless. 
O. Lemma I-veined; lower glume 1,—2/3 as long as the upper. 
CALAMOVILFA (p. 49) 
OO. Lemma 5-veined; lower glume 34 to equaling the upper. 
CALAMAGROSTIS (p. 45) 
MM. Lemma without hairs at base. 
P.  Palet half as long as its lemma or shorter, often none; glumes exceeding 
the lemma; stamens 3. AGROSTIS (p. 47) 
PP.  Palet over half as long as its lemma; glumes not exceeding the lemma 
(except in Cinna latifolia). 
Q. Seed tightly enclosed by the ovary; stamen 1; lemma with a very 
small dorsal awn. CINNA (p. 46) 
QQ. Seed loosely enclosed by the ovary; stamens 2—-3: lemma awnless. 
SPOROBOLUS (p. 44) 
ARISTIDA 3-AWNED GRASS 
Annual or perennial, tufted. Leaves narrow, often involute. Spikelets narrow, 
on slender pedicels or nearly sessile, in a terminal panicle; rachilla jointed above the 
glumes. Glumes persistent, keeled, unequal, awnless or somewhat acuminte-awned. Lem- 
ma usually with a blunt hairy callus at the base, narrow, rigid, entire, awned: awn 
terminal, trifid, its lateral branches sometimes obsolete. Palet small, obsolete, 2-veined. 
Stamens 3. Grain narrow, free. (L. arista—awn.) 
A. Annual; lower glume about 2.5 cm. long, 3—5-veined. E. 
A. oligantha Michx. (Prairie 3-awn) 
‘AA. Perennial; lower glume 0.6—I1I cm. long, 1-veined. 
B.* Awns of lemma nearly equal, about 7 cm. long; glumes cleft at apex. E. 
