1. Cirsium horridulum Michx. Bull thistle, yellow thistle. 



Winter annual or biennial, 1-10 dm. tall, rarely taller; stems commonly 5-10 

 mm. thick basally; flowering stem commonly solitary at the base, rarely much- 

 branched above, usually with a solitary terminal head; leaves in over-all outline 

 often broadly linear to lanceolate or oblanceolate, pinnatifid with shallow spiny 

 lobes; heads subtended closely by a false involucre or calyculum of large very 

 spiny appressed bracteal leaves as long as or longer than the true involucre; 

 involucre 4-8 cm. broad; phyllaries of the true involucre all with weak flat tips; 

 corolla pinkish or yellowish. Cardum spinosissimus Walt. 



In wet meadows and depressions, in water at edge of ponds and lakes, in Okla. 

 (Ottawa and McCurtain cos.) and e. and s.e. Tex. and coastal part of Rio Grande 

 Plains, Mar.~May; mostly on the Coastal Plain, Me. to Tex. and e. Okla. 



2. Cirsium muticum Michx. Swamp-thistle. 



Biennial supposedly; stems thick and hollow, 4-30 dm. tall; leaves thinnish, 

 very deeply pinnatifid, the lobes almost half the total breadth; involucre ovoid- 

 cylindric, 20-35 mm. high; outer phyllaries blunt and merely subulate-mucronate, 

 not spiny-tipped; flowers purple or rarely whitish. 



Very rare in moist sand, usually acid areas, in swamps and wet meadows and 

 seepage areas, in e. Tex., July-Oct.; s.w. Can. and n.e. U.S. s. to N.C., Tenn., 

 La. and Tex. 



3. Cirsium inornatum (W. &. S.) W. & S. 



Biennial about 1 m. tall; stem stout, simple below but above with a few ascend- 

 ing branches, striate, sparingly arachnoid, becoming nearly glabrous with age; 

 basal leaves narrowly oblanceolate, with remote triangular spine-tipped teeth; 

 lower cauline leaves linear-lanceolate, to about 18 cm. long and 2 cm. wide, with 

 a few remote triangular spine-tipped teeth, the margins beset with fine spines, 

 glabrous beneath except on midvein, sparingly villous above with long weak white 

 hairs; upper cauline leaves lanceolate to oblong, acute or subacuminate, sessile 

 and clasping the base, the auricles rounded, the margins irregular and bearing 

 numerous slender yellow spines; heads few, occasionally solitary at end of the 

 branches but usually in clusters of about 3, pedunculate, campanulate, about 2.5 

 cm. high and slightly less broad, subtended by numerous spiny reduced bracteate 

 leaves; phyllaries of involucre in several series, successively shorter outward; 

 outer phyllaries linear-lanceolate with long-attenuate tips, mostly glabrous on the 

 back, rarely slightly arachnoid, spine-tipped, the margins bearing weak yellow 

 spines; inner phyllaries broader, scaberulous, mostly abruptly dilated at the tips 

 into a lanceolate or oval often laciniate spine-tipped portion; corollas yellow; 

 achenes obovate, compressed, brownish, 4-5 mm. long, the pappus about 10 mm. 

 long. 



In wet meadows, edge of streams and in seepage areas, in N.M. (Otero and 

 Taos COS.), June-Sept.; apparently endemic. 



4. Cirsium Parryi (Gray) Petrak. 



Perennial or (?) biennial 3-10 dm. tall; stems more or less arachnoid-pubescent; 

 leaves lanceolate to oblong-lanceolate, sinuate-dentate to sinuate-lobed, with 

 spines 2-15 mm. long, glabrate; heads solitary or 2 to 4 clustered at end of stem 

 and branches, occasionally in the upper axils, 2-3 cm. high and about as wide; 

 involucre phyllaries rather densely arachnoid, with a glutinous dorsal ridge; 

 phyllaries (at least some) spinulose-ciliate, with a terminal spine 1-5 mm. long, 

 with at least some of the inner phyllaries with a dilated fringed tip; corollas light 

 greenish-yellow. 



In wet meadows, on seepage slop>es and in conifer forests, in N.M. {Blake) and 



1695 



