858 QOMPOSITAE (COMPOSITE FAMILY) 



6. Leaves entire or sparingly sinuate-lobed (only the basal sometimes deeply 



. pinnatifid.} 



7. C. altfssimum (L.) Spreng. Biennial; stem downy, branching, 1-3.8 m. 

 high ; leaves roughish-hairy above, whitened with close wool beneath, oblong- 

 ovate to narrowly lanceolate, undivided, sinuate-toothed, or undulate-pinnatifid, 

 the lobes or teeth with weak prickles ; involucre 2-3 cm. high ; outer bracts with 

 a short dark glandular line on the back, abruptly tipped by a spreading setiform 

 prickle ; inner with a lanceolate or deltoid usually serrulate tip; flowers chiefly 

 purple. (Carduus L. ; Cnicus Willd.) Fields and copses, Mass, to Minn., 

 Neb. , and south w. 



8. C. iowSnse (Pammel) Fernald. Similar, but with larger heads ; involucre 

 3-3.5 cm. high; bracts with broad long dark glandular back; the inner with a 

 prolonged linear- or lance-attenuate colorless tip. la., S. Dak., and Kan. 



= = Heads on naked peduncles. 



9. C. virgini^num (L.) Michx. Stem woolly, slender, simple or sparingly 

 branched, 0.3-1 m. high, the branches or long peduncles naked; leaves lanceo- 

 late, green above, whitened with close wool beneath, ciliate with prickly bristles, 

 entire or sparingly sinuate-lobed, sometimes the lower deeply sinuate-pinnatifid ; 

 heads small; outer bracts scarcely prickly; flowers purple. (Carduus L. ; 

 Cnicus Pursh.) Woods and plains, Va., O., and southw. 



f- - Leaves green both sides, or only with loose cobwebby hairs underneath; 

 heads large ; bracts scarcely prickly-pointed. 



10. C. milticum Michx. (SWAMP THISTLE.) Stem tall, 1-2.5 m. high, 

 angled, smoothish, panicled at the summit ; branches sparingly leafy, bearing 

 single or few rather large heads ; leaves somewhat hairy above, whitened with 

 loose webby hairs beneath when young, deeply pinnatifid, the divisions lanceolate, 

 acute, cut-lobed, prickly-pointed ; bracts of the toebby and glutinous (sometimes 

 glabrate) involucre closely appressed, pointless or barely mucronate ; flowers 

 purple. (Carduus Pers. ; Cnicus Pursh.) Swamps and low woods, common, 

 July-Sept. Var. suBpiNNAxfriDUM (Britton) Fernald. Leaves slightly lobed, 

 not deeply pinnatifid. (Carduus muticus, var. Britton.) Nfd. to W. Va. 



11. C. pumilum (Nutt.) Spreng. (PASTURE or BULL THISTLE.) Biennial; 

 stem low and stout, 3-9 dm. high, hairy, bearing very large heads (4-8 cm. 

 broad), which are often leafy-bracted at the base; leaves green, lanceolate- 

 oblong, partly clasping, somewhat hairy, pinnatifid, with short and cut very 

 prickly-margined lobes ; outer bracts prickly-pointed, rarely a little glutinous on 

 the backs, the inner very slender ; flowers purple or rarely white, fragrant, 

 6 cm. long; anthers scarcely acuminate; roots terete, solid. (Cnicus odoratus 

 Muhl., nomen subnudum; Carduus odoratus Porter.) Dry fields, N. E. to Pa. 

 and Del. July-Sept. 



12. C. Hillii (Canby) Fernald. Similar to the preceding, perennial, rarely 

 with more than 1 head ; leaves less deeply and more bluntly pinnatifid, with 

 finer and shorter prickles ; bracts with a conspicuous dark glutinous line down 

 the back; anthers acuminate; perpendicular root fusiform, hollow. (Cnicus 

 Canby ; Carduus Porter. ) Fields, Ont. to Minn., s. to Pa., 111., and la. 



* * * * Outer bracts of the appressed involucre barely prickly-pointed ; heads 

 mostly small and numerous. 



i- None of the leaves strongly decurrent. 



13. C. ARVENSE (L.) Scop. (CANADA THISTLE.) Perennial, slender, 3-9 

 dm. high, the rootstock extensively creeping; leaves oblong or lanceolate, 

 smooth, or slightly woolly beneath, finally green both sides, strongly sinuate- 

 pinnatifid, very prickly-margined, the upper sessile hut smrrcly decurrent ; heads 

 imperfectly dioecious ; flowers rose-purple or whitish. ( Carduus Robson ; 

 Cnicus Hoffm.) Cultivated fields, pastures, and roadsides, common; a most 

 troublesome weed, extremely difficult to eradicate. (Nat. from Eu.) Var. VES- 

 T!TUM Wimm. & Grab. Leaves permanently white-lanate beneath. Locally 

 established. (Nat. from Eu.) Var. INTEGRIF6LIUM VVimm. & Grab. Leaves 



