202 COMPOSITE. 



56. CIRSIUM. Tourn. Thistle. 



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

 heal that disease.) 



Heads many-flowered; the flowers perfect or dioecious. 

 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. lanceolatum 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. Cactus 

 lanceolatus Linn. Cnicus lanceolatus 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. aUissimum Spreng. : stem tall, branched, pubescent ; leaves ciliate- 

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

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

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

 altusimus Willd. 



Old fields. Penn. to Car. W. to Miss. Aug., Sept. 1\.. Stem 38 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. Carduiis discolor Nutt. Cnicus discolor 

 MuJd. 



Old fields. Can. to Car. July Sept. .Stem 36 feel high, sparsely 

 hairy. Heads 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. Leaves very thorny. Heads numerous, terminal, small. Flowers 

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



Canada Thistle. Cursed Thistle 



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 muticus Nutt. 

 C. glutinosus Deck Bot. 1st. Ed. 



