192 CAMPAXULALES 



Leaves entire or lobed, the lower sometimes pinnatifld. 



2. C. altissimus. 

 Leaves deeply pinnatifld into linear or lanceolate segments. 

 Leaves floccose but green above, strongly spiny. 



3. C. flodmanii. 

 Leaves glabrous above, weakly spiny. 4. C. discolor. 



Leaves tomentose on both sides, or becoming glabrous above. 

 Leaves pinnatifld. 



Spines of the involucre less than half as long as the bracts. 

 Flowers pink or purple. 

 Heads not over 5 cm. broad. 5. C. undulatus. 



Heads larger, 5-8 cm. broad. 



5a. C. undulatus var. megacephalus. 

 Flowers yellow. 6. C. plattensis. 



Spines of the involucre as long as the bracts, yellow. 



7. C. ochrocentrus. 



Leaves entire or undulate. 8. C. nebraskensls. 



Bracts of the involucre not strongly prickly pointed, heads small, not 



over 25 mm. broad, dioecious. 



Leaves very prickly with stiff prickles. 9. C. arvensls. 



Leaves scarcely prickly, prickles not stiff. 



9a. C. arvensis var. setosus. 



1. Carduus lanceolatus L. Common Bur Thistle. 

 Introduced in the southeastern part of the state. Nebraska City. 



2. Carduus altissimus L . Tall Thistle. 

 Common in fields and along roadsides in the eastern part of the state. 

 Ainsworth; Dismal River; Holt County; Lincoln; Nebraska City; 

 Newark; Valentine. 



3. Carduus flodmanii Rydb. 



In river bottoms and meadows. Arcadia; Minden; Newark; Antelope 

 County. 



4. Carduus discolor (Mihl.) Nutt. Field Thistle. 

 Common over most of the state. Gordon; Grand Island; Scotts Bluff; 

 Red Cloud; Weeping Water. 



5. Carduus undulatus Nutt. White Thistle. 

 On plains and prairies throughout the state. Boelus; Deuel County; 

 St. Paul; Squaw Canon; Utica. 



5a. Carduus undulatus megacephalus (A. Gray.) Porter. 

 Ainsworth; Niobrara; Red Cloud. 



6. Carduus plattensis Rydb. 



In the sand-hills. Glen; Kennedy; Minden; O'Neill; Box Butte 

 County; Paddock; Thedford; Valentine. 



7. Carduus ochrocentrus (A. Gray.) Greene. 

 Callaway; Indianola; Minden; Riverton. 



8. Carduus nebraskensls Britton. 



In the western part of the state. Scotts Bluff. 



9. Carduus arvensis (L.) Robs. Canada Thistle. 

 Introduced in the eastern part of the state. Lincoln; Nebraska City; 

 Omaha; Plainview; St. Paul. 



9a. Carduus arvensis var. setosus. 

 Bethany; College View. 



