638 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



Subgenus 2. Dichanthelium Hitchc. and Chase 



Perennial, from a crown, rarely from short matted rhizomes, surrounded by a 

 more or less well-marked rosette of usually short winter leaves, in spring 

 producing simple culms with mostly narrowly lanceolate blades .and 

 terminal panicles with numerous spikelets, these rarely perfecting seed 

 (or occasionally in Lanuginosa group and in P. clandestinum) ; early culms 

 branching at some or all of the nodes (in a few species from the base only) 

 after the maturity of the primary panicles or sometimes before; branches 

 often repeatedly branching, the short branchlets more or less fascicled 

 and bearing usually much reduced leaves; the terminal one or two joints 

 of the primary culm often finally falling, the whole producing an autumnal 

 phase usually strikingly different from the vernal phase; secondary pani- 

 cles reduced, the latest more or less included in the sheaths, the spikelets 

 cleistogamous and perfecting their grains. The species of this subgenus 

 are usually known as dichotomous panicums because they are related to 

 Pa nicu m dichotomum . 



Key to the species of subgenus 2 irrespective of the groups 



la. Spikelets glabrous. 

 2a. Spikelets 3 mm. long or more, strongly nerved. 



Spikelets pointed; blades elongate 5. P. depauperatum. 



Spikelets blunt; blades not elongate. 



Spikelets 3.2 to 3.3 mm. long; blades firm; sheaths, or some of them, hispid. 



95. P. SCRIBNERIANUM. 



Spikelets not more than 3 mm. long; blades rather thin; sheaths glabrous or sparsely 



hispid 94. P. helleri. 



2b. Spikelets less than 3 mm. long. 



3a. Second glume and sterile lemma exceeding the fruit and pointed bevond it. Spike- 

 lets 2.2 to 2.9 mm. long. 



Blades clustered toward the base 26. P. nudicaule. 



Blades not clustered toward the base. 



Sheaths, at least the secondary, hispid 106. P. scabriusculum. 



Sheaths glabrous. 



Blades firm; fruit 1.5 mm. long 107. P. cryptanthum. 



Blades thin; fruit nearly 2 mm. long 35. P. yadkinense. 



3b. Second glume and sterile lemma not pointed beyond the fruit. 

 4a. Ligule manifest, 1 to 3 mm. long. 



Culms rather stout ; ligule 2 to 3 mm. long ; sheaths glabrous 40. P. spretum. 



Culms slender; ligule 1 mm. long; sheaths sparsely pilose 83. P. curtifoliu.m. 



4b. Ligule obsolete. 



5a. Spikelets 1.5 mm. or less long. 



Nodes bearded 27. P. microcarpox. 



Nodes not bearded. 



Culms and blades pilose 13. P. strigosum. 



Culms glabrous. 



Blades conspicuously ciliate; plants branching at base only. 



12. P. POLYCAULON. 



Blades not ciliate; plants branching from middle or upper nodes. 



Vernal culms 50 cm. tall or more; spikelets turgid, strongly nerved; 

 autumnal phase erect, with fascicled branches shorter than the 



primary internodes 37. P. caerulescens. 



Vernal culms usualty much less than 50 cm. tall; autumnal phase spread- 

 ing or reclining. 

 Spikelets 1.1 to 1.2 mm. long; blades rarely as much as 5 cm. long. 



84. P. CHAMAELONCHE. 



Spikelets 1.2 to 1.4 mm. long. 



Blades elongate, at least some of them 8 to 10 cm. long. 



85. P. GLABRIFOLIUM. 



Blades not more than 3 cm. long 81. P. ensifolium. 



5b. Spikelets 2 mm. long or more. 



Blades elongate, some of them 20 times as long as wide; spikelets 2.2 to 2.8 mm. 

 long. 



