188 CYPERACEAE (SEDGE FAMILY) 



Only the outermost scale awned 8. S. Clintordl. 



All the scales awned 4.-5. planifoliua. 



b. Perianth-bristles ligulate and barbless ; scales chartaceous, the midrib 



of at least the outer prolonged into a rigid awn. 

 Culms terete and smooth at tip ; achene 2 mm. long, slightly ex- 

 ceeded by the perianth 5. S. caespiiosus. 



Culms trisronous and scabrous above; achene about 1 mm. long ; 



the perianth becoming 2-3 cm. long &. S. hudsonianui. 



Involucre foliaceous or appearing to be a contintiation of the culm c. 



c. Involucral bract 1 (occasionally with a secondary small involucel), ap- 



pearing to be a continuation of the culm d. 



d. Spikelet solitary ; culms flaccid 1. S. mibtermindlis. 



d. Spikelets normally more than 1 ; culms firm e. 



e. Spikelets crowded into a subterminal short spike .... 8. S. rufus. 

 6. Spikelets distinct, paniculate or glomerulate f. 

 f. Spikelets sessile or in glomerules g. 



g. Annuals with tufted roots ; culms terete or obtusely angled. 



Achenes transversely wrinkled 9. <S. Ilallii. 



Achenes smooth or inerelj' pitted. 



Achenes unequally biconvex or lenticular. 



Bristles surpassing the achene 10. 5. debilis. 



Bristles wanting (10) S. debilis, v. Williamaii. 



Achenes plano-convex, one face distinctly flattened. 



Bristles wanting 11. S. Smithii. 



Bristles present (11) S. Smithii, v. setoaua. 



g. Perennials with running rootstocks ; culms sharply trigonous A. 

 h,. Involucral leaf erect. 



Involucral leaf 4-15 cm. long ; spikelets pointed. 

 Scales reddish-brown, ciliate, awn-tipped ; achene plano- 

 convex, broadly obovoid, short-mucronate . . 12. S. americanus. 

 Scales yellowish-brown, entire, mucronate ; achene 



trigonous, oblong-obovoid, long-mucronate . . 13. S. Torreyi. 

 Involucral leaf 1-3 cm. long; spikelets obtuse . . . 14. S. Olneyi. 



h. Involucral leaf strongly divergent 15. S. mueronatus. 



f. Spikelets more or less loosely umbeUulate or paniculate i. 

 i. Culms triangular, from a short rootstock ; basal sheath bear- 

 ing a long triangular leaf ; involucral leaf keeled, much 



overtopping the loose umbel 16. >S. etuberculatua. 



i. Culms and short involucral leaf terete, the latter shorter than 

 the 1-sided compound umbel-like panicle of tawny spike- 

 lets ; basal sheaths mostly bladeless j. 

 j. Achenes lenticular ; bristles 4-6, subequal, about as long as 

 the achenes. 

 Achenes 2 mm. long, nearly equaling the scales . . 17. S. validua. 

 Achenes 2.5-3 mm. long, much exceeded by the scales . 18. S. occidentalis. 

 j Achenes trigonous ; bristles very unequal, mostly shorter 



than the achenes 1^. S. heterochaetus. 



C. Involucral bracts 2 or more, leaf-like ; culms leafy Tc. 

 h. Spikelets large, 1-5 cm. long, 0.5-1 cm. thick ; midrib of the scales 

 extended beyond the somewhat lacerate or 2-cleft apex as an 

 awn ; culms sharply trigonous ; rootstocks cord-like, with fre- 

 quent tuber-like thickenings. , 

 Achenes sharply and equally trigonous . . _ . . . .20. S.fluviahha. 

 Achenes lenticular, plano-convex or obscurely trigonous. 

 Scales of the spikelets rufescent, bearing numerous elongate 



red markings 21. S. rohustua. 



Scales whitish to castaneous, not rufescent. 



Scales whitish-brown 22. S. campestris. 



Scales drab to castaneous. 

 Spikelets all or mostly in a dense glomerule . (22) ^S'. campeatria, v. paludoaua. 

 Spikelets 1-several on mostly elongate rays. 

 Spikelets long-cvlindric, 2-5 cm. long (22) S. ea?npestri$, v. novae-angllae. 



Spikelets ovoid,' 1-2 cm. long .... (22) S. campestris, v. Fernaldi. 

 h. Spikelets small, 2-15 mm. long, 1-3 mm. thick, very numerous, in 

 decompound umbelliform panicles I. 

 I. Bristles retrorsely barbed ; spikelets in glomerules ; culms mostly 



solitary ; the short caudex bearing thick scaly stolons m. 

 m. Lower sheaths (at least) red-tinged ; bristles barbed nearly to 

 base n. 

 n. Achenes lenticular ; style-branches 2 ; bristles 4. 



Primary and secondary rays of the inflorescence mostly 



elongate, the ultimate glomerules mostly peduncled . 23. S. rubrotinctus. 

 Primary and secondary ravs abbreviated, most of the ulti- 

 mate glomerules crowded in irregular masses (23) S. rubrotinctus,\. conforms, 

 n. Achenes trigonous ; style-branches 3 ; bristles 3 or 6. 



Spikelets narrowlv ovoid, 3-5 mm. long . . . .24. S. sylvaUcito. 

 Spikelets cylindric, 6-14 mm. long . . . (24) S. sylvatiaiis, v, MsscJClU 

 m. Sheaths uniformly greenish, not red ; bristles barbed only above 

 .^e middle ^. 



