HITCHCOCK AND CHASE — NORTH AMERICAN PANICUM. 



21 



First glume very small, not over one-fourth the 

 length of the small, obovate, blunt spike- 

 let; tropical species. (See also P. repens with 



pointed spikelets) See Parviglumia, 



p. 124. 

 First glume as much as one-third the length of the 

 spikelet (shorter in P. repens). 

 Spikelets pubescent. 



Fruit silky-villous; spikelets 6 to 7 mm. long, 



densely villous 75. P. urvilleanum. 



Fruit smooth and shining; spikelets not over 

 3.5 mm. long. 

 Culms and sheaths glabrous or softly pubes- 

 cent; blades ovate-lanceolate 78. y P. millegrana. 



Culms and sheaths densely harshly villous; 



blades linear 80. P. rudgei. 



Spikelets glabrous. 

 Sterile palea enlarged and indurated at ma- 

 turity, expanding the spikelet; blades 

 scarcely wider than their sheaths. 

 Spikelets 3 mm. long, congested; panicles 



dark purple 63. P. cupreum. 



Spikelets not over 2.4 mm. long; panicles 

 green or pale. 

 Panicle branches spikelet or branchlet- 

 bearing along the upper half or toward 



the ends only 62. P. hians. 



Panicle branches branchlet - bearing 



throughout their length or nearly so. 61. P. exiguifiorum. 

 Sterile palea, if present, not enlarged and 

 indurated. 

 Plants forming conspicuous creeping, scaly 

 rootstocks. 

 Spikelets long - pediceled, not secund, 

 arranged in open or contracted 



panicles See Virgata, p. 84. 



Spikelets short-pediceled, more or less se- 

 cund along the nearly simple panicle 

 branches. 

 Panicles open; spikelets 3.4 to 3.8 

 mm. long (shorter in exceptional 



specimens) 55. P. anceps. 



Panicles more or less contracted; spike- 

 lets not over 2.8 mm. long 56. P. rhizomatum. 



Plants not forming creeping, scaly rootstocks. 

 Fruit, crested at the apex; spikelets 5.5 to 



6 mm. long; tropical species 195. P. zizanioides. 



Fruit not crested. 



