PIPER FLORA OF THE STATE OF WASHINGTON. 609 



SILYBUM. 



1. Silybum marianum (L.) Gaertn. Fruct. & Sem. 2: 378. 1802. Milk thistle. 



Carduus mariana L. Sp. PI. 2: 823. 1753. 



Type locality: "In Angliae, Galliae, Italiae aggeribus ruderatis." 

 Specimens examined: Pullman, Piper in 1902; Vancouver, Piper in 1904. 



CARDUUS. Thistle. 



Dioecious; heads small; perennial by spreading roots 1. C. arvensis. 



Hermaphrodite; heads larger; biennials. 



Bracts of the involucre all with dilated fringed tips 2. O. americanus. 



Bracts of the involucre or some of them with spiny tips. 



Outer and inner bracts all with spiny tips 3. C. lanceolatus. 



Outer bracts spine-tipped; inner ones unarmed. 



Involucre loose, the outer bracts nearly or quite as long 

 as the inner. 



Heads clustered, short-peduncled; flowers pink 4. Cedulis. 



Heads few, long-peduncled; flowers cream-color.... 5. C . remotif alius. 

 Involucre close, the outer bracts much shorter than the 

 inner. 



Heads clustered, subsessile, leafy; bracts herbaceous, 



not glandular on the back 6. C. foliosus. 



Heads not clustered, peduncled; bracts, coriaceous, 

 glandular on the back. 



Outer bracts with spines nearly as long 7 . C. ochrocentrus. 



Outer bracts with much shorter spines. 



Leaves canescent on both sides; flowers 



usually pink 8. C. undulatus. 



Leaves green above; flowers whitish 9. C. palousensis. 



1. Carduus arvensis (L.) Robs. Brit. Fl. 163. 1777. Canada thistle. 

 Serraiula arvensis h. Sp. PI. 2: 820. 1753. 



Cnicus arvensis Hoffm. Deutschl. Fl. ed. 2. 1^: 130. 1804. 

 Cirsium arvense Scop. Fl. Carn. ed. 2. 2: 126. 1772. 

 Type locality: European. 



Specimens examined: Pullman, Piper, July 1, 1895; Tacoma, Piper. 

 The Canada thistle is now well established in various places in Washington, but it pro- 

 duces good seed only exceptionally, and therefore its spread is slow. 



2. Carduus americanus (A. Gray) Rydberg, Bull. Torr. Club 28: 508. 1901. 

 Cnicus carlinoides americanus A. Gray, Proc. Am. Acad. 10: 48. 1874.' 

 Cnicus americanus A. Gray, Proc. Am. Acad. 19: 56. 1883. 



Type locality: "Rocky Mountains of Colorado." 



Range: Washington to California and New Mexico. 



Specimens examined: Seattle, Piper in 1888; Goose Lake, Flett 1097. 



3. Carduus lanceolatus L. Sp. PI. 2: 821. 1753. Bull thistle. 



Cnicus lanceolatus Willd. Prod. Fl. Berol. 259. 1787. 



Cirsium, lanceolatum Scop. Fl. Carn. ed. 2. 2: 130. 1772. 



Type locality: European. 



Specimens examined: Pullman, Piper, August, 1897; abundant in western Washington. 



4. Carduus edulis (Nutt.) Greene, Proc. Acad. Phila. 1892: 362. 1893. , 

 Cirsium edule Nutt. Trans. Am. Phil. Soc. 7: 420. 1841. 



Cnicus edulis A. Gray Froc. Am. Acad. 10: 47. 1874. 



Type locality: " The plains of Oregon and the Blue Mountains " Collected by Nuttall. 

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