COMPOSITAE 



637 



Pappus-bristles not plumose. 

 Filaments united below. 

 Receptacle fleshy, not bristly. 

 Achenes obliquely inserted on the receptacle. 

 Heads not subtended by bristly leaves. 

 Heads sessile, subtended by bristly leaves. 



52. Arctium L. 



Bracts densely cottony; heads corymbose. 

 Bracts usually glabrous; or slightly woolly. 



Involucre 25 mm. broad or more; inner bracts equalling or ex- 

 ceeding the flowers. 

 Involucre 10-20 mm. broad; inner bracts not exceeding the 

 flowers. 



54. Carduus. 



55. Mariana. 



56. Okopordon. 



57. Centaurea. 



58. Cnicus. 



1. A. iomcntosuh 



2. A. Lappa. 



3. A. minus. 



1. A. tomentosum (Lam.) Schk. In waste places: N. B. to Mass. 



and southern N. Y. to Pa. Adventive from Europe. 

 Occasional as a weed. 



2. A. Lappa L. In waste places: N. B. and Ont. to southern N. 



Y. and locally in the interior. Native of Europe. 



In N. Y. and Conn, as a weed, apparently wanting elsewhere in 

 our range. 



3. A. minus Schk. In waste places: E. N. Am. Native of 



Europe. 



Abundant as an often pernicious weed throughout the area. 

 A. nemorosum Lejeune has been collected as a waif in Conn. 



O 



53. Cirsium [Tourn.] Mill. 



Outer involucral bracts, or all of them prickle-pointed. 

 Leaves glabrous or hispid above, tomentose beneath. 



All the bracts of the involucre tipped with prickles; 



naturalized weed. 

 Outer bracts prickle-tipped, the inner merely acu- 

 minate; nativs species. 

 Leaves undivided, lobed or dentate, rarely pin- 



natifid. 

 Leaves deeply pinnatifid into lanceolate or linear 

 segments. 

 Leaves green on both sides, somewhat pubescent beneath. 

 Bracts of the involucre not at all prickly-pointed or scarcely so. 

 Heads large, few, 3-10 cm. broad; flowers all perfect and 

 fertile. 

 Heads involucrate by the upper, very spiny leaves; 



flowers usually yellow. 

 Heads peduncled, naked or with one or two bracts at 



I. C. lanceol turn. 



2. C. altissimum. 



C. discolor. 

 C. odoratum. 



5. C. horridulum. 



