GENUS 17. GRASS FAMILY. 135 



II. VERRUCOSA. 



A single species in our range ; spikelets tuberculate. 3. P. vernicostim. 



III. CAPILLARIA. 



Spikelets lanceolate or elliptic, i)4" long or less. 



Leaves glabrous. 4. P. dichotomiflorum. 



Leaves pubescent. 



Spikelets ij4" long or less, panicles broad. 



Panicle large and diffuse, occupying more than one half of the plant. 5. P. capillare. 

 Panicle not occupying over one third of the plant, usually exserted from the sheath. 

 Spikelets i" long or more; culms stout; blades 4" -5" wide. 7. P. Gattingeri. 

 Spikelets less than i" long; blades i"-3" wide. 8. P. philadelphicum. 



Spikelets ij4"-i&" long. 



Panicle narrow, its branches ascending or nearly erect. 9. P. flexile. 



Panicle open, diffuse, broader than long, its branches spreading or the lower ones 



reflexed. 6. P. barbipuhinatum. 



Spikelets ovate, 2"-2 J / 2 " long. 10. P. miliaceum. 



IV. HALOPHILA. 



Culms densely tufted; spikelets about 2^4" long. n. P. amarulum. 



Culms scattered, from stout branching rootstocks ; spikelets 2 l / 2 "-$" long. 12. P. amarum. 



V. VIRGATA. 

 Stems tall, simple; panicle usually ample. 13. P. virgatum. 



VI. AGROSTOIDEA. 



Rootstocks present. 14. P. anceps. 



Rootstocks wanting. 



Fruiting scale sessile. 



Panicle broad, open, its branches spreading. 



Ligule naked; culms finally much-branched; spikelets numerous. 15. P. agrostoidcs. 

 Ligule ciliate ; culms simple or sparingly branched; spikelets few. 17. P. longifolitim. 

 Panicle oblong, narrow, dense, its branches erect. 16. P. condcnsum. 



Fruiting scale distinctly stalked. 18. P. stipitatum. 



VII. DlCHOTOMA. 



Culms simple, or with basal branches and panicles only; not fasciculately branched later. 



Spikelets acute, usually over i l / 2 " long, the second and third scales extending beyond the 



fruiting scale. 19. P. depauperatum. 



Spikelets obtuse, rarely acutish, i}/" long or less; outer scales not exceeding fruiting scale. 

 Secondary panicles present. , 



Panicle-branches erect; spikelets obtuse, about 1^/2" long. 20. P. pcrlongum. 

 Panicle branches spreading; spikelets acutish, i"-i>4" long. 21. P. linearifolium. 

 Secondary panicles wanting. 



Leaf-sheaths glabrous or merely ciliate on the margins. 



Blades ciliate their entire length ; plants yellowish green. 24. P. ciliatinn. 

 Blades not ciliate or sparingly so at the very base ; plants green or grayish green. 

 Spikelets less than i" long. 



Panicle much longer than broad ; upper blades not smaller than the lower ones. 



32. P. polyanthes. 

 Panicle nearly as long as broad, upper blades smaller than the lower ones. 



31. P. sphaerocarpon. 

 Spikelets i" long or more. 



Blades linear, less than 2^/2" wide. 22. P. Werneri. 



Blades linear-lanceolate, 3"-io" wide. 



Panicle narrow, its branches appressed. 64. P. xanthophysum. 



Panicle broad, open, its branches spreading. 23. P. Bicknellii. 



Leaf-sheaths spreading-hirsute. 



Spikelets glabrous, Yn" long; culms hirsute. 25. P. strigositm. 



Spikelets pubescent, about i" long; culms glabrous. 26. P. laxiflorum. 



Culms simple only at first ; later with fasciculate branches at the upper nodes. 

 Middle blades of main culm less than 8" wide, the base rounded to subcordate. 

 Blades of the main culm usually elongated and narrowed at both ends. 

 Plants large; culms over 3 long; leaf-blades up to 8' long. 



Spikelets i*4" long, very acute, strongly nerved. 69. P. scabriusculum. 



Spikelets i 1 /*" long, barely acute, less strongly nerved. 70. P. aculeatum. 

 Plants small; culms under 3 long; leaf-blades rarely exceeding 4' long. 

 Spikelets pubescent, narrowed at the base. 



Spikelets i" long; mature state of the blades involute. 28. P. aciculare. 

 Spikelets iJ4" long; mature blades flat, or involute only on the margins. 



Nodes not barbed ; branches of the panicle spreading. 27. P. angustifoliutn. 

 Nodes barbed ; branches of the panicle ascending. 29. P. consanguineum. 

 Spikelets glabrous, not narrow at the base. 30. P. Bushii. 



Blades of the culm not elongated nor conspicuously narrowed at the base. 

 Spikelets less than iY 2 " long. 

 Spikelets glabrous. 



Spikelets strongly nerved, acute ; blades up to 8' long. 69. P. scabriusculum. 

 Spikelets relatively obscurely nerved, obtuse ; blades rarely exceeding 4' long. 

 Nodes densely barbed ; spikelets about 34" long. 38. P. microcarpon. 

 Nodes naked, or rarely the lowermost ones sparingly barbed. 



Spikelets usually less than }$" long. 42. P. octonodum. 



Spikelets i" long: 



Obovoid ; culms puberulent. 60. P. Nashianum. 



Elliptic ; culms glabrous. 



