202 COMPOSITE. 



56. CIRSIUM. Towm.— Thistle. 



<.From the Greek Ktpaos, a swelled vein ; on account of its being supposed to 

 heal that disease.) 



Heads many-flowered; the flowers perfect or dicecious. 

 Scales of the involucre more or less spinous at the summit. 

 Receptacle bristly. Corolla with the tube short and the border 

 5-cleft. Achenia oblong, compressed, smooth, not ribbed. Pap- 

 pus of numerous plumose bristles, deciduous. 



* Leaves dccurrent. 



1. C. Imiceolatum Scop. : stem branched, hairy ; leaves decurrent pinna- 

 tifid, hispid above, woolly beneath ; segments divaricate and spinous ; scales 

 of the involucre linear-lanceolate, spinous, outer ones spreading. Carduus 

 lanceolatus Linn. Cnicus lanceolakts Willd. 



Fields and road sides. N. S. July — Oct. %. — Stem 2 — 4 feet high, winged 

 by the decurrent leaves. Heads terminal, ovoid, middle-sized. Flowers purple. 



Common Thistle. 



** Leaves sessile. 



2. C. altissimum Spreng. : stem tall, branched, pubescent ; leaves cihate- 

 spinous, scabrous above, tomentose beneath ; radical petioled, pinnatifid ; 

 cauline sessile, oblong-lanceolate, sinuate-toothed ; scales of the involucre 

 ovate-lanceolate, spinous, appressed. Carduus altissimus Linn. Cnicus 

 altissimus Willd. 



Old fields. Penn. to Car. W. to Miss. Aug., Sept. %.—Stem 3—8 feet 

 high, and on the Missouri, according to Mr. Nuttall, 12 — 18 feet. Leaves varia- 

 ble. Heads large, terminal. Flowers purple. Tall Thistle. 



3. C. discolor Spreng. : stem hairy, divaricately branched ; leaves lan- 

 ceolate, sessile or clasping, more or less deeply pinnatifid, smoothish above, 

 tomentose beneath ; segments 2-lobed, ciliate and spinous ; involucre sub- 

 globose ; the scales ovate, spinous. Carduus discolor Nutt. Cnicus discolor 

 Muht. 



Old fields. Can. to Car. July— Sept. (^.—Stem 3—6 feet high, sparsely 

 hairy. iiea<Zs large, terminal. Flowers purple. , Two-colored Thistle. 



4. C. arvense Scop. : stem paniculate ; the branches somewhat woolly , 

 leaves oblong-lanceolate, sessile, sinuate-pinnatifid, spinous, undulate, 

 smoothish ; involucre ovoid ; scales ovate-lanceolate, the outer armed with 

 a short spine. Carduus arvensis Smith. Cnicus arveusis Willd. 



Fields and road sides. Can. and N. S. July. %. — Root creeping. Stem 

 2 — 3 feet high. Z/caves very thorny. ifeatZ* numerous, terminal, small. Floioers 

 purple, rarely whitish. A very troublesome weed. Introduced from Europe. 



Canada Thistle. Cursed ThistU 



5. C. muticum Mich. : stem smoothish, sparingly branched ; leaves ses- 

 sile, deeply pinnatifid, woolly beneath ; segments lanceolate, acute, spinu- 

 lose ; involucre subglobose ; scales viscid, woolly, unarmed, or the outer 

 ones with a very short spine. C. Bigelowii D. C. Carduus miUicus Nutt. 

 C. glutinosus Beck Bat. \st. Ed. 



