56 CYPERACEAE 



b. Leaves, at least their sheaths, pubescent : naturalized species. 



32. C. hirla. 



X. ATRATAE. 

 A single species in our rangre. 33. C.fusca. 



XI. RIGIDAE. 

 Lower leaf- sheaths becoming very fibrillose. 34. C. siricla. 

 Lower leaf -sheaths not at all fibrillose or only sparingly so. 



Scapes 3-6 dm. tall : scales acute or acuminate. 35. C. Haydeni. 

 Scapes 2-1 1 dm. tall : scales at least the upper ones obtuse. 

 Scales green. 36. C. aquatilis. 



Scales brown or purple. 37. C. Goodenovii, 



XII. PRASINAE. 

 Perigynia twisted toward the top : scales purple-brown. 



Perigynia straight : scales green. 



XIII. PENDULINAE. 

 Pistillate spikes narrowly cylindric. 

 Pistillate spikes oblong or globular. 



Perigynia surpassing the scales. 



Perigynia shorter than the scales. 



XIV. CRYPTOCARPAE. 

 Perigynia obovoid, obtuse. 

 Perigynia oblong or elliptic, acute. 



XV. VIRESCENTES. 

 Perigynia densely pubescent. 

 Pistillate spikes oblong-cylindric, 8-20 mm. long : perigynia oval or ovoid, 



few-nerved. 45. C. virescens. 



Pistillate spikes narrowly cylindric, 1 2-36 mm. long : perigynia oblong, 

 strongly many-nerved. 46. C. costellata. 



Perigynia glabrous or nearly so, at least when mature. 

 Spikes 5-7 mm. thick : perigynia imbricated, flattened : top of the achene 



not bent. 47. C. triceps. 



Spikes 3-4 mm. thick : perigynia not imbricated, swollen : top of the achene 

 "bent or tipped with a bent style. 48. C. Caroliniana. 



XVI. GRACILLIMAE. 



Perigynia 2 mm. long, slightly swollen : spikes linear or linear-cylindric. 

 Plants glabrous : perigynia obtuse. 49. C. gracillima. 



Plants with pubescent sheaths : perigynia pointed at both ends. 



50. C. aestivalis. 

 Perigynia4-5 mm. long, manifestly swollen : spikes oblong or oblong-cylindric. 



51. C. Davisii. 



XVII. SYLVATICAE. 



A single species in our range. 52. C. longirosiris. 



XVIII. DEBILES. 

 a. Perigynia membranous, few-nerved : pistillate spikes slender. 

 Perigynia Vi longer than the scales : leaf-blades 5-10 mm. wide. 



53. C. arctata. 

 Perigynia % longer than the scales : leaf-blades 2-5 mm. wide. 



54. C. tenuis. 



