CYPERACE^E. (SEDGE FAMILY.) 553 



3. C YPERUS proper. Style 3-cleft : achenium triangular : spikes many-flow- 

 ered, flat or almost terete; only the lowest scale empty ; the joints of the axis wing- 



* Stamen only one: spikes short and small (2" -3", or becoming 4" -5" long), col- 



lected in globular heads, ovate or linear-oblong, compactly many-flowered: the 

 scales merely ascending on the naked marginless axis. 



*- Low atmuals : involucre 2 - 3-leaved : heads' few: scales pointed. 



6. C. inflexus, Muhl. Dwarf (!'- 5' high); spikes oblong becoming linear, 

 7-13-flowered, in 1-5 ovate heads (either sessile and clustered or short-pedun- 

 cled) ; scales nerved, tapering into a long recurved point ; achenium obovate, obtuse. 

 Sandy wet shores : common. Sweet-scented in drying. 



7. C. acuminatUS, Torr. Slender (3' -12' high); spikes ovate, becoming 

 oblong, 16-30-flowered, pale; scales obscurely 3-nerved, short-tipped ; achenium 

 oblong, pointed at both ends. Low ground, Illinois and southwestward. 



*- 1- Tall perennial (l-4 high): heads many, greenish: scales pointless. 



8. C. vlrens, Michx. Culm either sharply or obtusely triangular; leaves 

 and involucre very long, keeled ; umbel compound, many-rayed ; spikes ovate 

 or oblong ; achenium oblong or linear ; scales acutish, obscurely 3-nerved. ( C. 

 vegetus, Torr.) Wet places, Virginia and southward. 



* * Stamens 3 : spikes 3-10 in a cluster at the summit of the culm or of each ray of 



an umbel, flat, oblong or linear, the crowded scales ascending, strongly keeled, 

 ovate, with abruptly sharp-pointed slightly-spreading tips: achenium broadly 

 obovate, sharply triangular. 



9. C. compressus, L. Low annual (3' -9' high), with a single sessile or 

 a few umbellate clusters of linear green spikes (of 6" - 10" long, 1 5 -30-flowered), 

 the axis naked. Sterile fields, Somerset Co., Maryland, W. M. Canby (also 

 ad\;entive near Philadelphia Navy Yard), and southward. 



10. C. dentatUS, Torr. Perennial, with running rootstocks (6' - 12' high) ; 

 clusters several or many in a simple or twice or thrice compound umbel ; spikes 

 ovate-oblong and rather few-flowered, or when well-developed linear and 1 5 - 30- 

 iflowered (3" -5" long); the scales reddish-brown with green back; joints of the 

 axis wing-margined. Sandy swamps, Massachusetts to Northern New York 

 <(J. A. Paine), and southward. Spikes often abortive and changed into leafy 

 tufts as in Juncus. 



* * * Stamens 3 : spikes narrowly linear, flat, scattered along the upper part of the 



rays of an open simple or somewhat compound umbel : scales oppressed, pointless: 

 joints of the spike wing-margined: perennial by slender running rootstocks, which 

 bear small nut-like tubers, by which the plants multiply pestiferously in cultivated 

 grounds. 



11. C. rotundus, L., var. Hydra. (NUT-GRASS.) Culm slender 

 < (i- 1 2 hig n )> longer than the leaves; umbel simple or slightly compound, 

 about equalling the involucre ; the few rays each bearing 4-9 dark chestnut-purple 

 12-40-flowered acute spikes (5" -9" long) ; scales ovate, closely oppressed, nerveless 

 except on the keel. ( C. Hydra, Michx. ) Sandy fields, Virginia and southward : 

 aod adventive near Philadelphia, C. F. Parker. (Eu.) 



