COMPOSITAE (^COMPOSlTE FAMILY) «57 



Herbs, mostly biennial ; the sessile alternate leaves often plnnatifid, prickly. 

 Heads usually large, terminal. Flowers reddish-purple, rarely white or yellowl 

 ish ; in summer. (Name i'rom Kipabs, a swelled vein, tor which the Tliistle waa 

 a reputed remedy.) Cnicus of many auth., not L. By some recent Am. auth. 

 included in Carduus. 



* Bracts of the involucre all tipped with spreading prickles. 



1. C. lanceoiAtum (L.) Hill. (Common or Bull Thistle.) Leaves decur. 

 rent on the stem, forming prickly lobed wings, piunatifid, rough and bristly 

 above, woolly with decitluous webby hairs beneath, prickly ; ilowers purple. 

 (Carduus L.; Cnicus Willd.) — Pastures and roadsides. July-Nov. (Nat* 

 from Eu.) 



* * Heads leafy-hracteate at base (see also no. 11); proper bracts not prickly. 



2. C. spinosissimum (Walt.) Scop. (Yellow Thistle.) Stout, 0.3-1.5 m. 

 high, webby-haired when young ; leaves partly clasping, green, soon smooth, 

 lanceolate, pinnatifid, the short toothed and cut lobes very spiny with yellowish 

 prickles ; heads 4-8 cm. broad, surrounded by very prickly bract-like leaves, 

 which usually equal the narrow involucral bracts ; flowers pale yellow or purple. 

 (Carduus Walt.; Cnicus horridulus Pursh.) — Sandy soil. Me. to Va., and 

 southw., near the coast; reported from L. Superior. June-Aug. 



* * * Bracts ajjpressed, the inner not at all prickly. 



•»- Leaves white-woolly beneath, and sometimes also above ; outer bracts succes- 

 sively shorter, spinose-tipped. 



++ Leaves white above. 



= Leaves pinnate, ivith linear mostly entire divisions. 



3. C. Pitcheri (Torr.) T. & G. White-woolly throughout, low; stem very 

 leafy ; leaves all pinnately parted^ into rigid narrowly linear and elongated 

 sometimes again pinnatifid divisions, with revolute margins ; inner invfilncral 

 bracts acumiyiate, generally to a weak prickle ; flowers cream-color. ( Cnicus 

 Torr.; Carduus Porter.) — Sandy shores of Lakes Michigan, Huron, and Supe- 

 rior. July, Aug. 



= = Leaves pinnatifid or pinnately parted, the lobes lanceolate or triangular. 



4. C. undulatum (Nutt.) Spreng. Resembling the preceding ; root biennial ; 

 leaves partly clasping, undivided, undulate-pinnatifid, or rarely pinnately parted, 

 moderately prickly ; involucre 2-3 cm. high ; bracts with a definite glandular 

 ridge on the back, and twice or thrice as long as the slender spreading prickle ; 

 flowers reddish-purple. (Carduus Nutt.; Cnicus Gray.) — Islands of L. Huron 

 to Mich., la., Kan., and westw. June-Oct. Var. megacephalum (Gray) 

 Feinald. Heads larger ; involucre 3-4.5 cm. high. — Minn, to Okla., Tex., and 

 westw. 



5. C. canlscens Nutt. Beep-rooted perennial; leaves narrower and more 

 deeply pinnatifid than in no. 4 ; involucre 2-2.5 cm. high, its narrow bracts end- 

 ing in very slender spines. — Minn, and w. la., westw. and southwestw. 



*+ ++ Leaves green above. 



= Stems leafy up to the heads. 



a. Leaves deeply pinnatifid into linear-lanceolate lobes. 



6. C. discolor (Muhl.) Spreng. Branching perennial, 1-2 m. high ; stem 

 strongly furrowed, hirsutulous ; basal leaves 3-4 dm. long, deeply pinnatifid, 

 the lobes often cleft ; upper leaves with somewhat falcate lobes, white-woolly 

 beneath ; heads mostly solitary at the tips of the branches; involucre 2.5-C-i cm. 

 high ; bracts appressed ; the outer tipped by a weak recurved prickle ; tlw inner 

 linear- or lance-attenuate, with a very long colorless entire appendage. ( Cardum 

 Nutt.; Cnicus altissimus, var. Gray.) — Rich soil, N. B. to Ont., Minn., and 

 southw. 



