194 MISC. PUBLICATION 243, U.S. DEPT. OF AGRICULTURE 
Racemes 1 to many, racemose or fascicled on the axis, not conjugate. 
Second glume warngin Gore a a ee eee eee nee 73. P. PULCHELLUM. 
Second glume developed. 
First glume developed on at least one of the pair of spikelets. 
Plants with stout scaly rhizomes; spikelets glabrous. First glume 
oltentobsoletes = oe aa ee ee ee ee 24. P. UNISPICATUM. 
Plants without rhizomes; culms more or less tufted. 
Spikelets not more than 2 mm long. 
Plants decumbent, creeping. 
First glume small, about equally developed on all spikelets 
2 P, DECUMBENS. 
First glume obsolete or only occasionally developed. 
21. P. NUTANS. 
Plants erect or ascending, not creeping. First glume of sec- 
ondary spikelet elongate: 22 2 82 es 22. P. DISPAR. 
Spikelets more than 2 mm long. Plants not decumbent. 
Spikeletsiglabrowswt jt) Wie ei) a 23. PP. PILOSUM. 
Spikelets sparsely pubescent______.___-____-- 25. P. LANGEI. 
First glume normally wanting. 
Racemes terminal and axillary, the axillary sometimes hidden in 
the sheaths; terminal inflorescence of 1 to 3, rarely 6, racemes. 
Plants rooting at the lower nodes _____.______-_ 21. P. NUTANS. 
Plants erect to widely spreading but not rooting at the nodes. 
Blades densely grayish-villous, not ciliate_-—-_-_ hie SPA DEBILE: 
Blades ciliate, not villous. 
Spikelets about 2 mm long, not pointed_18. P. cILIATIFOLIUM. 
Spikelets about 1.8 mm long, slightly pointed. 
19. P. PROPINQUUM. 
Racemes terminal on the primary culm or leafy branches, no truly 
axillary racemes. 
Plants annual. 
Spikelets with a broad firm notched margin. 74. P. FIMBRIATUM. 
Spikelets not margined. 
Spikelets not more than 1.5 mm long, elliptic; fruit pale. Plants 
annual. 
Spikelets solitary. 
Spikelets orbicular, usually beaded with globular hairs. 
48. P. MULTICAULE. 
Spikelets elliptic, not beaded-_---_- 50. P. PARVIFLORUM. 
Spikelets impairs. 42 Sos Bane 49, P. CLAVULIFERUM. 
Spikelets 2 to 3 mm long; fruit dark brown. 
Spikelets 2.4 to 3 mm long, commonly appressed-pubescent. 
a P. CONVEXUM. 
Spikelets not more than 2.2 mm long, glabrous. 
Rachis searcely 1 mm wide.__.71. P. MELANOSPERMUM. 
Rachis 2 to 2.5 mm wide..-------- 72. P. BOSCIANUM. 
Plants perennial. 
Racemes solitary, subcylindric; spikelets solitary (sometimes 
paired in P. saugetiz). 
Plants stoloniferous. Culms rarely more than 10 em tall. 
Glume and sterile lemma not beaked nor wrinkled. 
P. BREVE, 
Glume and sterile lemma beaked beyond the fruit, deeply 
nig aNU cg Calo Maka Gotan doy 6 858 pA Ce ES Nyasa 52. P. EDMONDI. 
Plants not stoloniferous. 
Sterile lemma wrinkled or crumpled. 
Foliage conspicuously pubescent; blades flat or subin- 
volute. 
Raceme cylindric; rachis straight_----- 43. P. NANUM. 
Raceme rather flat, scarcely cylindric; rachis flexuous. 
44, P. INSULARE. 
Foliage glabrous or nearly so; blades concavo-convex in 
cross section. 
Glume and sterile lemma scarcely crumpled. 
40. P. FILIFORME 
