COMPOSITAE (^COMI'OSITE 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 /ctpo-os, a swelled vein, for which the Thistle was 

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

 included in Carduus. 



* Bracts of the involucre all tipped with spreading prickles. 



1. C. lanceolXtum (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, pricklj^ ; flowers purple. 

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

 from Eu.) 



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



2. C. spinoslssimum (Walt.) Scop. (Yellow Thistle.) Stout. 0.8-1.5 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, 

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

 (Cardnus Walt.; Cniciis horridulus Pursh.) — Sandy soil. Me. to Va., and 

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



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



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

 sively shorter, spi nose-tipped. 



+-^ Leaves white above. 



= Leaves pinnate, with linear mostly entire divisions. 



3. C. Pitchiri (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 (Xutt. ) Spreng. Resembling the preceding ; root biennial ; 

 leaves partly clasping, undivided, undulate-pi nnatifid, 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 3-4.5 cm. high. — Minn, to Okla,, Tex., and 

 "westw. 



5. C. can6scens Nutt. Deep-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. 



•^ -M- 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 sometJjhat 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, uiith a very long colorless entire appendage. ( Carduus 

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

 southw. 



