GENUS 104. THISTLE FAMILY. 553 
13. Cirsium horridulum Michx. Yellow Thistle. 
Fig. 4648. 
Carduus spinosissimus Walt. Fl. Car. 194. 1788. Not Cir- 
sium spinosissimum (L.) Scop. 
Cirsium horridulum Michx. Fl. Bor. Am. 2: 90. 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, 14’-2%’ 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- WW \ 
ida and Texas. Abundant along the edges of salt-meadows y -: NNN I 
ie ae York and New Jersey. May-Aug., or earlier in the | \ 
South. y A - 
14. Cirsium miticum 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, Ill. Fl. 3: 489. 1898. 
Gareeses muticus alpicola Fernald, Ott. Nat. 1905: 
I . 
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 13’ 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 arvénse (L.) Scop. Canada Thistle. Creeping Thistle. Fig. 4650. 
Serratula arvensis L. Sp. Pl. 820. 1753. 
Cirsium arvense Scop. Fl. Carn. Ed. 2, 2: 126. 1772. 
Carduus arvensis Robs. Brit. Fl. 163. 1777. 
Cnicus arvensis Hoffm. Deutsch. Fl. Ed. 2, 1: Part. 2, 
130. 1804. 
Perennial by horizontal rootstocks, forming patches, 
nearly glabrous, or the leaves sometimes woolly be- 
neath; stems striate, 1°-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, 5’-8’ long; heads numerous, corymbose, dioe- 
cious, I’ broad or less, nearly 1’ 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. 
