234 COMPOSITACEAE (COMPOSITE FAMILY) 



Style unbranched or the branches appendaged. Pappus none or chaff or 

 stiff bristles or capillary bristles, simple or plumose 



A. Involucre bracts hooked at tip; leaves not spiny. ARCTIUM (p. 234) 



AA. Involucre bracts not hooked at tip, 

 B. Leaves not spiny. 

 C. Pappus at least partly of plumose bristles. 

 D. Leaves entire or dentate; heads 1-3 cm. wide. W. C. E. — (Honor of H. B. 

 de Saussure, a Swiss botanist.) Saussurea americana (saw-wort) 



DD, Leaves pinnatifid; heads 5-10 cm. wide. W. — Heads edible. (Gk. kyon = 

 a dog; the involucre spines suggest dog-teeth.) Cynaria scolymus (artichoke) 

 CC. Pappus none or of simple bristles or scales. CEWTATJREA (p. 235) 



BB. Leaves somewhat spiny and often also the involucre. 

 E. Pappus distinctly plumose. 



F. Heads 1-5 cm. wide; involucre bracts not fleshy; akenes not ribbed. 



CARDTJTJS (p. 234) 

 FF. Heads 5-10 cm. wide; involucre bracts fleshy; akenes slightly ribbed. (See 

 DD.) Csmaria scolymus (artichoke) 



EE. Pappus none to barbellate or fimbriate. 



G. Heads 6-7 cm. wide; leaves green and blotched with white, W. E. — (Gk. 

 silyhos = the name of a thistle with edible stem.) 



Silybum marianum (lady's thistle) 

 GG. Heads 2-4 cm. wide; leaves not white-blotched. 

 H. Heads not subtended by bristly leaves. CENTAUREA (p. 235) 



HH. Heads subtended by bristly leaves, sessile. U. E. — (Gk. kniso = to prick.) 



Cnlcus benedictus (blessed thistle) 



ARCTIUM (Burdock) 



Tall, coarse. Leaves broadly ovate, cordate at base, 2-5 dm. long. 

 Heads clustered ; receptacle densely bristly. Pappus-bristles short, many, 

 rough, deciduous, in i whorl. — (Gk. arktos = a bear; from the rough 

 involucre.) 



A. Heads racemose, 1.5-3 cm. wide. W. A. minus (common burdock) 



AA. Heads corymbose, 2-5 cm. wide. W. A. lappa (great burdock) 



CARDUUS (Thistle) 



Stout, erect. Heads rayless, all alike (or dioecious in C. arvensis). Re- 

 ceptacle flat, densely bristly. Flowers white or red or rarely yellowish. 

 Pappus bristles many, long, in i whorl, united into a ring at base. — (The 

 Latin name; said to be from Celtic ard = a sharp point.) 



A. Perennial by spreading horizontal rootstocks; heads 15-25 mm. high, dioecious. 

 W. E. — One of our worst weeds in cultivated fields. C. arvensis (canada thistle) 

 AA. Biennial; heads larger, all alike. 

 B. None of the involucre bracts spine-tipped, all with dilated fringed tips. W. E. 



C. americanus 

 BB. Outer involucre bracts spine-tipped, inner ones not. 

 C. Involucre bracts not at all glandular on the back. 

 D. Involucre bracts either nearly equal or some with spreading herbaceous tips. 

 E. Flowers cream-colored. W, C. E, C remotifoUus 



