188 CYPERACEAE (SEDGE FAMILY) 



Only the outermost scale awned 3. S. flintonii. 



All the scales awned 4. ,S'. 



6. 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. 



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



the perianth becoming '2 -3 cm. long G. /S. 



a. Involucre foliaceous or appearing to be a continuation 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 7. S. 



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



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



e. Spikelets distinct, paniculate or glomerulate /. 

 /. Spikelets sessile or in glomerules g. 



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



Achenes transversely wrinkled 9. S. Hallii. 



Achenes smooth or merely pitted. 

 Achenes unequally biconvex or lenticular. 



Bristles surpassing the achene 10. S. debilix. 



Bristles wanting (10) S. debilit, v. Williamnii. 



Achenes plano-convex, one face distinctly flattened. 



Bristles wanting 11. S. Smithii. 



Bristles present (in S. Smithii, v. tietosux. 



g. Perennials with running rootstocks ; culms sharply trigonous 1i. 

 h. Involucral leaf erect. 



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

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

 convex, broadly obovoid, short-inucronate . . 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. mucronatus. 



f. Spikelets more or less loosely umbellulate 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. elubercitfdtti*. 



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. 

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



the achenes. 



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

 Achenes 2.5-8 mm. long, much exceeded by the scales . 18. S. occhlt nt<tUx. 

 j. Achenes trigonous ; bristles very unequal, mostly shorter 



than the achenes 19. S. Jieterochattns. 



c. Involucral bracts 2 or more, leaf-like ; culms leafy k. 

 k. 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.fluriatili*. 



Achenes lenticular, plano-convex or obscurely trigonous. 

 Scales of the spikelets rufesceut, bearing numerous elongate 



red markings 21. S. robusfux. 



Scales whitish to castaneous, not rufescent. 



Scales whitish-brown 22. 



Scales drab to castaneous. 



Spikelets all or mostly in a dense glomerule . (22) S. cdmpestris, v. 

 Spikelets 1-several on mostly elongate rays. 

 Spikelets long-cylindrio, 2-5 cm. long (22) N. c<t/n/>t '.v/r/\, v 

 Spikelets ovoid, 1-2 cm. long .... (22) S. campestri*, \. 

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



decompound mnbelliform panicles I. 

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



solitary; the short caudex bearing thick scalv stolons HI. 

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



base n. 

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



Primary and BOdODOCry rays of the intlo-.-esceiice mostly 



elongate, the ultimate glomerules mostly pcdmicled ". 23. S. 

 Primary and secondary rays abbreviated, most of the ulti- 

 mate glomerules crowded in irregular masses (28) S. ri<ltrot//<ct .v, v. i-oi(f'crtns. 

 n. Achenes trigonous ; style branches ;i ; bristles :; or (1. 



Spikelets narrowly ovoid. :'.-'> mm. long . . . .24. S. n.i/f niti'di*. 

 Spikelets cylindrie, <>-14 mm. long . . . ('J4) X. Ki/lrtitii-n', \ . />//.*< ////. 

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

 the middle <>. 



