FERNALD. — CARICES OF SECTION HYPARRHENAE. 463 



O Perigynia thin and scale-like, barely distended over the achenes, 

 one-fourth to one-third as broad as long. 



Perigynia 7 to 10 mm. long (1) C. muskingumensis. 



Perigynia shorter (2) C. scoparia. 



(For vars. see above.) 

 O O Perigynia firmer, obviously distended over the achenes, nearly 

 or quite half as broad as long. 

 + Perigynia lance-ovate, about half as broad as long. 

 X Leaves 2.5 mm. broad, or broader .... (10) C. mirabilis. 



(For vars. see above.) 

 X X Leaves narrower. 



§ Perigynia distinctly about 10-nerved on the inner faces, 

 4 to G mm. long. 

 Spikelets 8 to 12 mm. long : perigynia 4.8 to 6 mm. 



long (12) C. tenera. 



Spikelets 5 to 8 mm. long : perigynia 4 to 5 mm. long 



(12) C. tenera, var. invisa. 

 § § Perigynia 3- to 5-nerved on the inner faces, mostly less 

 than 4 mm. long. 

 Perigynia with ascending inconspicuous tips 



(11) C. straminea. 

 Perigynia with divergent conspicuous tips 



(11) C. straminea, var. echinodes. 

 + + Perigynia with broad-ovate to orbicular bodies. 



X Spike moniliform and flexuous, with mostly clavate-based 

 spikelets. 

 Spikelets brownish-white ; of close-appressed obscurely 



beaked firm perigynia (14) C. silicea. 



Spikelets ferrugineous ; the abrupt slender beaks of the 

 perigynia with conspicuous loosely ascending or spread- 

 ing tips (12) C. tenera, var. Richii. 



X X Spike stiff (or, if flexuous, with brown or ferrugineous 

 spikelets). 

 § Perigynia 5.6 to 7.7 mm. long, very thin, scale-like, al- 

 most transparent : scales blunt . . . (13) C. Bicknellii. 

 § § Perigynia less than 5.6 mm. long, firm and opaque 

 (when exceptionally longer in C. alata, with aristate 

 scales). 

 □ Scales long-acuminate or aristate : perigynia 4 to 5.5 

 mm. long : achenes oblong. 

 A Spike green, or finally dull brown: scales lance- 

 subulate : perigynia obovate, 2.8 to 3.7 mm. broad, 

 abruptly narrowed at base .... (15) C. alata. 

 A A Spike dark brown or ferrugineous : perigynia 2.3 to 

 2.8 mm. broad. 



Spikelets closely approximate: scales ovate-lance- 

 olate : perigynia ovate, tapering gradually to 

 the beak . . . . (15) C. alata, var. ferruginea. 



