48(44). Perigynia firm, tough-membranous, only slightly acuminate 



44. C. hyalinolepis. 



48. Pergynia thin or papery, acuminate (49) 



49(48). Perigynia finely and closely ribbed; pistillate scales with scabrous awns 

 equal to or longer than the body of the scales (50) 



49. Perigynia coarsely ribbed; pistillate scales blunt to cuspidate or short-awned 



(53) 



50(49). Perigynia closely investing base of achenes, not inflated, greenish, be- 

 coming pale-brown, the teeth arched-divergent; leaves strongly sep- 

 tate-nodose; ligules prolonged 45. C. comosa. 



50. Perigynia loosely investing achenes, inflated, straw color or yellow-green; 



leaves less conspicuously septate-nodose; ligules about as broad as 

 long (51) 



51(50). Perigynia 2.5-4 mm. thick, about 10-nerved 48. C. lurida. 



51. Perigynia less than 2 mm. thick, with 12 to 20 nerves (52) 



52(51). Perigynia 5-7 mm. long, inflated, the beak about 2 mm. long; body of 

 pistillate scales small 46. C. hystericina. 



SI. Perigynia 4-5 mm. long, slightly inflated, the beak 1.5 mm. long; body of 

 pistillate scales large 47. C. Thurberi. 



53(49). Perigynia 8-20 mm. long (54) 



53. Perigynia 3.5-8 mm. long (58) 



54(53). Perigynia subulate to slenderly lanceolate, 1-3 mm. thick, delicately 

 nerved, barely inflated 51. C. folliculata. 



54. Perigynia lanceolate to ovoid or flask-shaped, 3-8 mm. thick, strongly 



nerved, usually much inflated (55) 



55(54). Plants densely cespitose, without elongate stolons; pistillate spikes glo- 

 bose or nearly so; style straight or slightly bent (56) 



55. Plants stout and leafy, with creeping stolons; pistillate spikes thick-cylindric 



or ellipsoid; style spirally bent (57) 



56(55). Perigynia cuneate at base, firm, opaque, dull-green, often hispidulous 

 52. C. Grayi. 



56. Perigynia rounded at base, membranous, lustrous, glabrous 



53. C. intumescens. 



57(55). Achene longer than wide, the angles prominent but not really knobby 

 54. C. hipidina. 



57. Achene wider than long, the angle definitely knobby 55. C. gigantea. 



58(53). Rhizomes without horizontal stolons; culms slender, rarely spongy-based; 

 leaves not conspicuously septate-nodulose; ligule longer than wide 

 49. C. vesicario. 



58. Rhizomes with long horizontal stolons; culms mostly thick and spongy at 



base; leaves prominently septate-nodulose; ligule as wide as long.... 

 50. C. rostrata. 



59(43). Spike solitary per culm 56. C. leptalea. 



59. Spikes 2 to numerous per culm (60) 



60(59). Achenes only obscurely 3-angled, with rounded or convex sides, slightly 

 pubescent, closely filling the bodies of the perigynia (61) 



60. Achenes definitely 3-anglcd, with flat or concave sides (62) 



61(60). Most of the culms short and hidden among the leaves; perigynia 3-4 

 mm. long 57. C nifyromarginata. 



61. Most of the culms not hidden among the leaves; perigynia 2.5-3 mm. long 



58. C. physorhyncha. 



494 



