POLYPETALOUS EXOGENOUS PLANTS. 295 



ing herhSj with palmately-divided long-petioled leaves, and 

 polygamous y?oz(^cr5 in small heads, disposed in a loose ex- 

 panding cyme. 



S. Marilandica, L. Leaves 5-7-parted, the divisions 

 lobed and toothed ; heads many-flowered ; sterile floiuers 

 numerous on slender pedicels ; stt/les long, recurved. Dry 

 woods. Stem 2°-3° high. 



S. Canadensis, L. Leaves 3-5-parted, the divisions 

 lobed and toothed; Jieads few-flowered; the sterile floioers 

 (1-3) nearly sessile ; styles short and straight. Dry woods, 

 common. May. /S'^ewi l°-2° high; branches of the c?/we 

 long and spreading. 



ERYNGIUM, Tourn. Button Snakeroot. 



Calyx 6-toot\ie(\, persistent; styles slender; /r?aY turbi- 

 nate, covered with scales or tubercles, without ribs or vittae. 

 — Herbs, with spiny or bristly mostly lobed or toothed leaves, 

 and white or blue bracted floiuers, closely sessile, in dense 

 heads. 



* F7tiit scaly ; stems erect. 



E. YiRGiNiANUM, Lam. Leaves linear-lanceolate, flat, 

 the lowest ones spiny-serrate with the teeth incurved, or 

 nearly entire, veiny ; the upper narrower, spiny or pinna- 

 tifid; leaves of the involucre (blue), 3-5-cleft, longer than 

 the head ; hrads 3-cleft, as long as the flowers. Perennial ; 

 stem 2°-3° high ; flowers blue. 



E. virgatu:m:, Lam. Leaves short, oblong or oblong- 

 ovate, serrate, the upper ones toothed or divided ; leaves of 

 the involucre entire, or with 2-4 bristly teeth, longer than 

 the head ; bracts 3-toothed ; stem l°-2° long ; leaves 2'-3' 

 long, sometimes cordate ; flowers blue. 



** Fruit granular ; stems diffuse. 



E. Baldw^inii, Spreng. Small, prostrate, branching; 



