COMPOSITAE (COMPOSITE FAMILY) 857 



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

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

 ish ; in summer. (Name from /a/xr6s, a swelled vein, for which the Thistle was 

 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. LANCEOLATUM (L.) Hill. (COMMON or BULL THISTLE.) Leaves decur- 

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

 above, woolly with deciduous webby hairs beneath, prickly ; flowers purple. 

 (Carduus L.; Cnicus Willd.) Pastures and roadsides. July-No v. (Nat. 

 from Eu.) 



* * Heads leafy-bracteate 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 

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



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



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

 sively shorter, spinose-tipped. 



H- Leaves white above. 

 = Leaves pinnate, with linear mostly entire divisions. 



3. C. PitchSri (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 involucral 

 bracts acuminate, 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) 

 Fernald. Heads larger ; involucre 3-4.6 cm. high. Minn, to Okla., Tex., and 

 westw. 



5. C. canSscens Nutt. Deep-rooted perennial; leaves narrower and more 

 deeply pinnatifid than in no. 4 ; involucre 2-2.6 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 2.5-3 cm. 

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

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

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

 southw. 



