GENUS 104. 



THISTLE FAMILY. 



13. Cirsium horridulum Michx. Yellow Thistle. 

 Fig. 4648. 



Carduus spinosissimus Walt. Fl. Car. 194. 1788. Not Cir- 



shim spinosissintum (L. ) Scop. 



Cirsium horridulum Michx. Fl. Bor. Am. 2: go. 1803. 

 Cnicus horridulus Pursh, Fl. Am. Sept. 507. 1814. 



Biennial or perennial, somewhat woolly when young, 

 but becoming glabrate; stem branched, leafy, 2-5 

 high. Leaves green both sides, lanceolate or oblong in 

 outline, sessile and clasping or the basal ones short- 

 petioled and somewhat spatulate, pinnatifid into trian- 

 gular or broader, spinulose-margined and prickle-tipped, 

 entire or dentate lobes ; heads involucrate by the upper 

 leaves, 2' -4' broad, ij'-ai' high; bracts of the involucre 

 narrowly lanceolate, roughish and ciliate, long-acumi- 

 nate, unarmed ; flowers pale yellow, yellowish, or occa- 

 sionally purple. 



In moist or dry sandy soil, Maine to Pennsylvania, Flor- 

 ida and Texas. Abundant along the edges of salt-meadows 

 in New York and New Jersey. May-Aug., or earlier in the 

 South. 



14. Cirsium muticum Michx. Swamp 

 Thistle. Fig. 4649. 



Cirsium muticum Michx. Fl. Bor. Am. 2: 89. 1803. 

 Carduus muticus Pers. Syn. 2:'386. 1807. 

 Cnicus muticus Pursh, Fl. Am. Sept. 506. 1814. 

 Carduus muticus subpinnatifidus Britton, in Britt. 



& Brown, 111. Fl. 3 : 489. 1898. 

 Cnicus muticus alpicola Fernald, Ott. Nat. 1905 : 



1 66. 



Biennial ; stem woolly or villous when young, 

 becoming glabrate, slender, striate, leafy, panicu- 

 lately branched above, 3-8 high. Leaves dense- 

 ly white-tomentose beneath when young, some- 

 times becoming glabrous on both sides, deeply 

 pinnatifid into lanceolate or oblong, entire, lobed 

 or dentate, spiny segments usually tipped with 

 slender prickles, or sometimes merely lobed ; 

 basal leaves petioled, 4'-8' long, those of the 

 stem sessile and smaller; heads about li' broad 

 and high, solitary, terminal, naked-peduncled, 

 or with a few small bract-like leaves near the 

 base ; outer bracts viscid, appressed, more or 

 less cottony, ovate or ovate-lanceolate, the in- 

 ner linear-lanceolate, acute, all unarmed ; flowers purple. 



In swamps and moist soil, Newfoundland to Florida, Saskatchewan and Texas. July-Oct. 



15. Cirsium arvense (L.) Scop. Canada Thistle. Creeping Thistle. Fig. 4650. 



Serratula arvensis L. Sp. PI. 820. 1753. 

 Cirsium arvense Scop. Fl. Cam. Ed. 2, 2: 126. 1772. 

 Carduus arvensis Robs. Brit. Fl. 163. 1777. 

 Cnicus arvensis Hoffm. Deutsch. Fl. Ed. 2, I : Part. 2, 

 130. 1804. 



Perennial by horizontal rootstocks, forming patches, 

 nearly glabrous, or the leaves sometimes woolly be- 

 neath; stems striate, i-3 high, branched above. 

 Leaves sessile, slightly clasping, but not decurrent, 

 lanceolate or oblong-lanceolate, deeply pinnatifid into 

 very prickly, lobed or dentate segments, or sometimes 

 nearly or quite entire; basal leaves sometimes peti- 

 oled, s'-8' long; heads numerous, corymbose, dioe- 

 cious, i' broad or less, nearly i' high, purple or white, 

 staminate heads globose, corollas projecting; pistil- 

 late heads oblong-campanulate, corollas shorter, the 

 long pappus conspicuous ; outer bracts ovate or ovate- 

 lanceolate, appressed, tipped with short prickly points, 

 inner bracts of the pistillate heads linear, elongated. 



In fields and waste places, Newfoundland to Virginia, 

 British Columbia, Nebraska and Utah. In many places 

 a pernicious weed. Races differ in leaf-form and in 

 pubescence. Naturalized from Europe. Way- or cursed 

 thistle. Corn-, hard- or prickly-thistle. June-Sept. 



