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



Autumnal phase topheavy-reclining; primary blades 6 to 10 mm. wide; second 

 glume equaling fruit and sterile lemma 34. P. barbulatum. 



7. Spreta 



Panicle narrow, one-fourth to one-third as wide as long 40. P. spretum. 



Panicle open, two-thirds as wide as long, or more. 



Spikelets 1.5 mm. long 41. P. lixdheimeri. 



Spikelets 1.3 mm. long or less. 



Culms and sheaths glabrous 43. P. loxgiligulattm. 



Culms and sheaths appressed-pubescent. 



Spikelets 1.2 to 1.3 mm. long 42. P. leucothrix. 



Spikelets not more than 1 mm. long 44. P. wrightiaxum. 



8. Lanuginosa 

 la. Spikelets not more than 2 mm. long. 

 2a. Plants grayish, velvety-pubescent. 



Spikelets 1.3 to 1.5 mm. long; autumnal blades involute-pointed (see also P. albe- 



marlense) 51. P. auburxe. 



Spikelets 1.8 to 2 mm. long; autumnal blades flat. 



Plants dark or olive green when dry ; spikelets 1 .9 to 2 mm. long.... 52. P. thtjrowii. 

 Plants light or yellow green when dry. 



Autumnal phase prostrate, branching from base and lower nodes, forming close 



mats; blades not ciliate. Around hot springs 57. P. thermale. 



Autumnal phase ascending or spreading, branching from middle and upper nodes, 



the reduced, fascicled blades strongly ciliate 50. P. laxugixosum. 



2b. Plants pubescent, often villous, but not velvety. 



3a. Culms conspicuously pilose with long, horizontally spreading hairs. Culms branch- 

 ing before expansion of primary panicles ..... 53. P. praecocius. 



3b. Culms variously pubescent, if pilose the hairs not long and horizontally spreading. 

 4a. Vernal blades glabrous or nearly so on the upper surface, firm in texture. 



Autumnal culms branching from the lower nodes, forming a spreading bunch 10 



to 15 cm. high; Pacific slope 55. P. occidextale. 



Autumnal culms branching from the middle nodes, forming widely spreading mats; 

 Atlantic slope (see also form of P. huachucae var. fasciculatum). 



49. P. texxesseexse. 

 4b. Vernal blades pubescent on upper surface, sometimes pilose near base and mar- 

 gins only. 

 5a. Spikelets 1.3 to 1.5 mm. long; vernal blades long-pilose on upper surface. 

 Autumnal phase widely decumbent-spreading, forming a mat ; vernal culms soon 



genieulate-spreading; plants olivaceous 46. P. albemarlexse. 



Autumnal phase erect or leaning, never forming a mat; plants yellowish green. 

 Axis of panicle pilose, panicle branches tangled, the lower drooping. 



47. P. IMPLICATUM. 

 Axis of panicle puberulent only, panicle branches not tangled, the lower 



ascending 45. P. meridioxale. 



5b. Spikelets 1.6 to 2 mm. long; vernal blades pilose or pubescent. 



Upper surface of blades pilose; spikelets 1.8 to 2 mm. long; autumnal phase 

 decumbent-spreading. 



Spikelets pointed; culms weak and lax 58. P. laxguidum. 



Spikelets obtuse; culms not weak and lax. 



Culms leafy below, branching from base and lower nodes; Maine to Minne- 

 sota 54. P. SUBVILLOSUM. 



Culms evenly leafy, branching from upper nodes; Pacific slope. 



56. P. PACIFICUM. 



Upper surface of blades appressed-pubescent or pilose toward the base only; 

 spikelets 1.6 to 1.8 mm. long; autumnal phase not decumbent-spreading. 



48. P. HUACHUCAE. 



lb. Spikelets 2.2 mm. long or more. 

 Spikelets 2.2 to 2.5 mm. long. 



Pubescence on culms horizontally spreading; autumnal phase freely branching. 



59. P. VILLOSISSIMUM. 



Pubescence on culms appressed or ascending; autumnal phase rather sparingly branch- 

 ing. _ 

 Upper internodes shortened, the leaves approximate, the blades often nearly equaling 

 the panicle. 

 Blades glabrous or nearly so on the upper surface; spikelets 2.2 to 2.5 mm. long; 

 first glume glabrous 60. P. bexxeri. 



