1918] The Grasses op Illinois 293 



g. Hairs on the culms and sheaths spreading horizon- 

 tally. P. villosissimum 

 gg. Hairs on the culms and sheaths not spreading hori- 

 zontally, but appressed or ascending. 



P. psetidopuiescens' 

 ff. Loaves not densely pubescent on both surfaces, the entire 

 plant not noticeably pubescent, 

 g. Blades ciliate, otherwise glabrous, or with a few fine 

 hairs; spikelets 2 mm. long; sheaths retrorsely 

 pilose ; blades very soft. P. xalapense 



gg. Blades broad, sometimes ciliate around the cordate 

 base; spikelets 2.5 to 3 mm. long; sheaths smooth; 

 blades firm. P. commutatum 



ec. Spikelets less than 2 mm. long. 



d. Culms and sheaths densely and usually conspicuously pubescent; 

 ligules densely hairy, 2 to 5 mm. long. 

 e. Spikelets more than 1..5 mm. long. 



f. Culms conspicuously pubescent with long, soft, horizon- 

 tally spreading hairs; blades pubescent, the hairs 

 nearly as long as the width of the 'blade; spikelets 1.8 

 to 1.9 mm. long. P. praecocvas 



ff. Culms and blades pubes-eent, with phort, appressed hairs, 

 g. Upper surface of blades smooth, or with only a few 

 hairs near base; blades with a thin, white margin; 

 spikelets 1.6 to 1.7 mm. long. P. tennesseense 

 gg. Upper surface of blades pubescent; blades never 

 with a thin, white margin; spikelets 1.6 to 1.8 mm. 

 long. P. htiachucae 



ee. Spikelets 1.5 mm. or less long. 



f. Summit of the culm with long hairs, panicle branches 

 tangled. P. implicatum 



ff. Summit of the culm without hairs; panicle branches not 

 tangled. P. meridionale 



g. Culms and sheaths not conspicuously pubescent, 

 either smooth or with f^hort, appressed hairs; ligules 

 (except in P. Undheimeri) generally very short, not 

 over 1.5 mm. long. 

 h. Spikelets not spherical, longer than broad; lig- 

 ules always visible; blades narrow, 

 i. Sheaths ciliate, otherwise glabrous or the 

 lower sparsel}'^ pilose, about half the length 

 of the internode; ligule densely hairy, 3 to 

 5 mm. long. P. Undheimeri 



ii. Sheaths appressed pubescent, very little 

 shorter than the internodes; ligules about 

 1 mm. long. P. tsrigetorum 



hh. Spikelets spherical or nearly so; ligules obsolete 

 or nearly so ; blades broad, 

 i. Panicle nearly as broad as long; blades not 

 distinctly nerved. P. sphaerocarpon 



ii. Panicle about two-thirds as broad as long; 

 blades distinctly nerved. P. polyanthes 



DICHOTOMIFLORA 



Only one species of this group is found in Illinois. These are 

 annual plants, typically smooth thruout, with largo, spreading panicles 

 4 to IG inches long. The leaves arc long and narrow, the ligules 1 to 

 3 mm. long, membranous, edged with a fringe of long hairs. The 

 first glume is very short, one-fourth or less the length of the spikelet. 



