191S] The Grasses of Illinois 291 



arc usually strongly nerved, and a very hard, shiny, fertile Icnnna 

 and palea inclosing the fruit, which are never nerved. This genus 

 was recently revised by Hitchcock and Chase (Contributions from the 

 U. S. Nat. Herb., Vol. 15, 1910). The Illinois species have been ar- 

 ranged in groups following their classification, then arranged alpha- 

 betically under the different groups. 



a. Spikelets smooth and glabrous. 



b. Plants never forming a winter rosette of leaves at the base of the culm, 

 the leaves all similar. 

 c. Plants annual, without creeping rootstocks. 



d. First glume not pver one-fourth the length of the spikelet, and 

 iisnally broadlv rounded at the apex, uovor sh;iri)-i)()iuted ; 

 plants generally smooth thruout. P. dichotomiflorum 



dd. First glume always one-half the length of the spikelet, or more; 

 ]>lants typically very pubescent, the sheaths usually papillof-e- 

 hirsute; panicles many-flowered, usually large, with fine capil- 

 lary branches, 

 e. Spikelets 4.5 to 5 mm. long, panicles often drooping. 



P. miliaceum 

 ee. Spikelets always less than 4 mm. long ; panicles never droop- 

 ing, numerous, one-third the entire height of the plant or 

 more, 

 f. Spikelets 2.5 or more long, usually at least 3 mm.; blades 

 sparsely pubescent, 

 g. Panicles as broad as long, leaves usually crowded at 

 the base of the plant. P. barbipulvinatum 



gg. Panicles narrow, usually less than half as broad as 

 long. P. flexile 



ff. Spikelets only rarely exceeding 2.2 mm. long; blades gen- 

 erally densely pubescent, 

 g. Culms slender; the panicles delicate, relatively few- 

 flowered ; spikelets less than 2 mm. long, usually in 

 pairs at the ends of the naked panicle branches. 



P. pMladelphicum 

 gg. Culms stout; panicles diffuse, many-flowered; spike- 

 lets 2 mm. or more long, 

 h. Panicles as broad as long, usually more than half 

 the length of the entire plant, mostly terminal 

 only. P. capillare 



hh. Panicles oval, seldom as broad as long, normally 

 one-third the length of the entire plant, or less, 

 produced from all the nodes. P. gattingeri 

 cc. Plants perennial, with or without creeping rootstocks. 



d. Panicles open, the spikelets long pediceled; culms from long, 



creeping rootstocks, not flattened. P. virgatum 



dd. Panicles somewhat contracted and resembling those of common 



redtop, {Agrostis alba) ; culms flattened, sheaths keeled. 



e. Long, scaly rootstocks present; spikelets 3.4 to 3.8 mm. long. 



P. anceps 

 ee. Eootstocks never present; spikelets 1.8 to 2 mm. long. 



P. agrostoides 

 bb. Plants forming a winter rosette at the base of the culm, these much 

 shorter and broader than the culm leaves. 

 c. Spikelets over 3 mm. long. 



d. Spikelets pointed or beaked; blades very long and narrow, usu- 

 ally stiff and erect from the base of the plant ; panicle narrow 

 and few-flowered. P. depaupcratum 



dd. Spikelets blunt; blades short and rather broad, distributed along 

 the culm ; panicle nearly as broad as long, but not densely 

 flowered. P. scribnerianum 



