15b. Ligule more than 3 mm. long 



117. Panicum amaralum — Bitter Panicgrass 



Leaves rolled in bud-shoot ; sheath round, smooth with a tuft of hairs 

 at throat, split with overlapping hyaline margins; auricles absent; collar 

 broad, divided; ligule a fringe of hairs, 3 to 8 mm. long, fused at base; 

 blade 8 to 13 mm. wide, smooth above and long hairy near base, smooth 

 below with midrib prominent, margins long hairy and hyaline. Inflores- 

 cence— a large, compact, densely flowered, slightly nodding panicle. 

 New Jersey south. Sandy shores and coast dunes. 



1 6a. Widest blades to 1 5 mm. wide 17 



16b. Widest blades more than 15 mm. wide 18 



1 7a. Blade rough above at least near tip 



118. Spartina pectinata — Prairie Cordgrass 



Leaves rolled in bud-shoot; sheath round, smooth, split with overlap- 

 ping margins; auricles absent; collar medium broad to broad, may be 

 hairy on margins; ligule a fringe of hairs, 2 to 4 mm. long, may be fused 

 at base; blade commonly 10 to 15 mm. wide, rough to very rough above, 

 smooth and mostly glossy below, margin smooth to very rough. Inflores- 

 cence — a series of comb-like spikes forming an appressed panicle. 

 Throughout. Fresh water marshes. 



17b. Blade smooth above. 



119. Panicum virga turn — Switchgrass 



Leaves rolled in bud-shoot; sheath round, smooth, split with overlap- 

 ping hyaline margins; auricles absent; collar broad, may be divided; 

 ligule a fringe of hairs, 2 to 4 mm. long; blade 10 to 15 mm. wide, smooth 

 above and mostly hairy near base, smooth below, margins smooth to 

 somewhat rough. Inflorescence — an open, widely spreading panicle. 

 Common throughout. Open ground and brackish marshes. 



1 8a. Blade margins very rough, a plant of salt 

 or brackish marshes 



120. Spartina cynosuroides — Big Cordgrass 



Leaves rolled in bud-shoot; sheath round, smooth, split with over- 

 lapping hyaline margins; auricles absent; collar broad, divided; ligule 

 a fringe of hairs, 3 to 3.5 mm. long, fused at base; blade to 30 mm. wide, 

 smooth above at least near base, smooth below with midrib prominent, 

 margins very rough and hyaline. Inflorescence— a series of comb-like 

 spikes forming a somewhat open panicle. Massachusetts south. Salt or 

 brackish marshes along coast. 



18b. Blade margins smooth to rough, not 

 of salt or brackish marshes 



19 



37 



