346 American Midland Naturalist Monograph No. 7 



68. Paspalum L. 



1. Rachis of the spikes dilated, thin, more than 2 mm broad, with 

 membranous marsfins. 



2. Spikelets pubescent. 1-1.5 mm long; blades 6-15 mm wide; 

 muddy banks or in shallow water in s. and w. III. Aug. -Oct. 

 P. fluitans (EUJ Kunth 



2. Spikelets glabrous, 2 mm long; blades 2-5 mm wide; in ditches 



or along muddy or sandy shores, s. 111. ; Perry, Pulaski, and 

 St. Clair counties P. dissectum L. 



1 . Rachis narrow, less than 2 mm broad ; spikelets glabrous. 



3. Spikelets 1.4-2.8 mm long; plant often with 1 -several axillary 



peduncles from the upper sheath. 



4. Spikelets orbicular; blades .sparsely pilose and ciliate; sandy 

 soil, roadsides, etc. July-Sept P. stramincum Nash 



4. Spikelets oval or somewhat obovate; blades glabrous or softly 

 pubescent on both sides. 



5. Blades glabrous; sandy soil or open woods in the centr. 

 counties P. ciliatijoliinn Michx. 



5. Blades softly pubescent; sandy soil; nearly throughout 111. 



July-Sept. [P. muJilenbergii Nash] P. pubescens Muhl. 



3. Spikelets 2.8-4 mm long; plant simple. 



6. Spikelets orbicular, arranged singly in 2 rows; wet ground, 



chiefly in the s. half of the state. July-Sept 



- - - P. circulare Nash 



6. Spikelets oval or slightly obovate, borne in pairs and appear- 

 ing as if in 3 or 4 rows. 

 7. Spikelets 3-3.2 mm long; ditches, s. 111., rare. Aug. -Sept. 

 [P. pubiflorum var. glabrum Vasey; P. lacuiglume 



Scribn.] P. geviinum Nash 



7. Spikelets 3.6-4 mm long; inoist soil in Perry and William- 

 son counties. [P. floridanurn Michx. var. glabratian 

 Engelm.] P. glabratum (Engelm.) Mohr 



69. Panicum L. — Panic Grass 



1. Spikelets glabrous (sparsely pubescent in P. dcpau pfrahim) . 

 2. Spikelets 3 mm or more in length. 



3. Plants glabrous, perennial, with rhizomes; panicle 15-50 cm 

 long; spikelets 4-4.5 mm long; roadsides and fields, com- 

 mon. July-Sept. Switch Grass ...P. virgaturn L. 



3. Plants more or less pubescent (except P. anccps and a var. of 

 P. depauperatum) . 

 4. Spikelets 4-5 mm long; panicles often drooping at matur- 

 ity; waste places; cidtivated and occasionally spontane- 

 ous; native of the Old World. Broomcorn Millet 



- - P. miliaceum L. 



4. Spikelets 3-3.8 mm long, lanceoloid, pointed; panicles erect. 



