858 coMPOSiTAE (composite family) 



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



pinnatijid.) 



7. C. altlssimum (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-pinnatiftd, 

 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 setiforui 

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

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

 Neb., and southw. 



8. C. iowense (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. virginianum (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. 



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

 heads large ; bracts scarcely prickly-pointed. 



10. C. muticum 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 pinnatijid, the divisions lanceolate, 

 acute, cut-lobed, prickly-pointed ; bracts of the webby 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. subpinnatifidum (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, pinnatijid, ivith 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, 

 5 cm. long; anthers scarcely acuminate; roots terete, solid. (Cuccus 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 but scarcely 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- 

 titum Wimm. & Grab. Leaves permanently white-lanate beneath. — Locally 

 established. (Nat. from Eu.) Var. integbif6lium Wimm. & Grab. Leaves 



