GRASSES OF IOWA. 



40 



Culms stout, panicle branches numerous, repeat- 

 edly dividing and bearing numerous spikelets. 



2-2.5 mm. long P.capillare.' 



Culms slender, panicle branches few, but little 

 divided, bearing comparatively few spikelets, 



1.5-2 mm. long P. minimum? 



tt Perennial, pedicels usually many times longer 



than spikelets P. cognatum!" 



bb. Spikelets ovate, 5 mm. long P. miliaceum. w 



b. Sheaths glabrous , P. proliferum." 



B. Culms simple, from stout scaly root-stocks P. virgatum}" 



Basal and culm leaves dissimilar, the former generally much 

 shorter and broader, rosulate tufts of leaves commonly 

 present in the fa 11, spikelets oval, obovate or globose, 

 obtuse except in P. depauperatum. 



A. Leaves linear, elongated, narrowed toward the base, erect, t^ie 



broader basal leaves rarely evident; panicles small, few- 

 flowered. 



a. Spikelets 3.5 mm. long, beaked, glabrous. P. depauperatum.™ 



b. Spikelets 3-3 25 mm. long, obtuse, glabrous or with a few 



scattered long hairs P. perlongum . l * 



q. Spikelets 2 2.5 mm. long, obtuse, pubescent. 



— P. lines rifoliu m . ' - 



B. Leaves narrowly to broadly lanceolate, rounded or claspirg at 



the base, usually spreading. 



a. Panicle strict, narrow, the branches appressed. 



— P. xanthophysum}* 



b. Panicle ovate, open, the branches spreading. 



t Leaf blades 2-4 cm. broad, cordate and clasping at the base. 



* Leaves glabrous or with scattered hairs, ciliate 



sheaths glabrous, ciliate nodes glabrous or 



the lower barbed P. macrocarpon .' T 



** Leaves and sheaths usually finely pubescent, 



nodes densely barbed P. latifolium .'" 



tt Leaf blades les« than 2 cm. broad, not cordate clasping. 

 a. Spikelets over 3 mm. long. 



Leaves pubescent on both surfaces. 



Leaves erect, rigid, thick, 3 4 mm. wide; spike- 

 lets 2 5 mm. long P. Wilcoxianum v ' 



Leaves mostly spreading, not thick, 5-10 mm. 

 wide, spikelets 3-3.5 mm. wide. 



—P Leibergii"* 

 Leaves glabrous or pubescent beneath 



— P. Scribnerianum.' A 



aa. Spikelets 2 mm. long P. Atlanticum}- 



aaa. Spikelets about 1.5 mm. long. 



Leaves thin, weak, papillate hairy beneath, spike- 

 lets pubescent P. lanuginosum.™ 



Leaves firm, densely pubescent beneath, spike- 

 lets pilose -P. unciphyllum.^ 



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