344 FLORA OF PHILADELPHIA. 



Philadelphia— Byberry, Mart. (B. C), Wissahickon (Je.), Germantown 

 (Me.), Greenwich Point (Te.). Bucks— Sellersville (Fr.). Delaware— 

 Media, Dr. Geo. Smith (Fu.), Lansdowne (Pe.)< 



Camden — Kaighn's Point. 



New Castle — Introduced about nurseries. 



53. ARCTIUM L. Burdock. 



Bracts of the involucre copiously woolly. 1. A. tomentosum. 



Bracts of the involucre glabrous or nearly so. 2. A. minus. 



1. Arctium tomentosum (Lam.) Schk. M. p. 1030. Waste places. Sum- 



mer. 

 Delaware— Media, Dr. Geo. Smith (P.). 



2. Arctium minus Schk. Common Burdock. M. p. 1030. Waste places. 



Summer and fall. 



54. CARDUUS L. Thistle. 



Pappus-bristles, at least those of the inner flowers, plumose. 



Outer involucral bracts, or all of them, strongly prickly-pointed. 

 Leaves glabrous or hispid above, tomentose beneath. 



All the bracts of the involucre tipped with prickles; natural- 

 ized weed. 1. C. lanceolatus. 

 Outer bracts prickle-tipped, the inner merely acuminate ; native 

 species. 

 Leaves undivided, lobed or dentate, rarely pinnatifld. 



2. C. altissimus. 

 Leaves deeply pinnatifld into lanceolate or linear segments. 



3. C. discolor. 

 Leaves green on both sides, somewhat pubescent beneath. 



4. C. odoratus. 

 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. 5. C. spinosissimus. 



Heads peduncled, naked, or with 1 or 2 bracts at the base; 

 flowers purple. 6. C. muticus. 



Heads small, numerous, 2.5 cm. broad or less; flowers imperfect, 

 dioacious. 7. C. arvensis. 



Pappus-bristles simple or minutely serrulate. 8. C. nutans. 



1. Carduus lanceolatus L. M. p. 1031. Pastures and roadsides. Sum- 



mer. 



2. Carduus altissimus L. M. p. 1031. Fields and copses. Summer. 



3. Cabduus discolor (Muhl.) Nutt. M. p. 1031. Fields and roadsides. 



Summer and fall. 



4. Carduus odoratus (Muhl.) Porter. M. p. 1032. Dry fields. Summer. 



5. Carduus spinosissimus Walt. Yellow Thistle. M. p. 1033. Sandy 



fields. Summer. 



Philadelphia— West Philadelphia (Mac), Germantown (St.), Angora 

 (Te.). Delaware — Williamson (Le.), Lansdowne (Pe.), Swarthmore 

 (Pr.), Middletown and Chrome Run (B. Sm.), Darby Creek ("VP.), Media 

 (Ws.), Wallingford (Wn.), Tinicum (St.). Chester- (P.). Lancaster 

 -(P.). 



Bwrlington — Pemberton (C), near Moorestown (B. Sm.). Camden — 



