548 



COMPOSITAE. 



VOL. III. 



3. Arctium minus Schk. Common Burdock. 

 Fig. 4635. 



Arctium minus Schk. Bot. Handb. 3: 49. 1803. 

 Lappa minor DC. Fl. Fran. 4: 77. 1805. 



Arctium Lappa var. minus A. Gray, Syn. Fl. i : Part 2 

 397- 1884. 



Smaller than the preceding species, seldom over 

 5 high. Leaves similar, the lower deeply cordate; 

 petioles hollow, not deeply furrowed ; heads numer- 

 ous, racemose on the branches, short-peduncled or 

 sessile, 6"-o/' broad; bracts of the involucre glabrous 

 or slightly cottony, the spines .of the outer ones 

 spreading, those of the inner erect and shorter than 

 the flowers; corolla-tube about as long as the limb. 



In waste places, common nearly throughout our area, 

 extending west to Colorado. Naturalized from Europe. 

 Called also cuckoo-button. Leaves rarely laciniate or 

 pinnatifid. July-Nov. 



104. CIRSIUM [Tourn.] Mill. Card. Diet. Abr. Ed. 4. 1754. 



Erect, branching or simple, prickly herbs, some species acaulescent, with alternate or 

 basal, sinuate-dentate, lobed or pinnatifid, usually very spiny leaves, sometimes decurrent, and 

 large, many-flowered, solitary or clustered, discoid heads of purple, yellow or white, tubular, 

 perfect and fertile, or rarely dioecious flowers. Involucre ovoid or globose, its bracts prickle- 

 tipped or unarmed, imbricated in many series. Receptacle flat or convex, bristly. Corolla- 

 tube slender, the limb deeply 5-cleft. Filaments pilose, or rarely glabrous. Anthers sagit- 

 tate at the base. Style-branches short or elongated, obtuse. Achenes obovate or oblong, 

 compressed or obtusely 4-angled, glabrous, smooth or ribbed. Pappus of several series of 

 slender, plumose bristles, connate at the base. [Greek, referring to the use of the thistle as 

 a remedy for swollen veins.] 



Over 200 species, widely distributed in the northern hemisphere. Besides the following, some 

 50 others occur in the southern and western parts of North America and many hybrids have been 

 described. Type species : Carduus heterophyllus L. 



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



i. Leaves glabrous or hispid above, tomentose beneath. 



All the bracts of the involucre tipped with prickles ; naturalized weed. i. C. lanceolatum. 



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

 Branches leafy up to the heads ; involucral bracts firm or rigid. 



Leaves undivided, lobed or dentate, rarely pinnatifid. 2. C. altissimum. 



Leaves deeply pinnatifid into lanceolate or linear segments. 3. C. discolor. 



Heads naked-peduncled, i' high: involucral bracts thin. 4. C.virginianum. 



2. Leaves tomentose on both sides, or becoming glabrous above ; western. 



Leaves pinnately parted ; segments linear, entire or lobed. 5. C. Pitcheri. 



Leaves pinnatifid into triangular or lanceolate dentate segments. 

 Outer bracts with spines less than one-half their length. 

 Leaf-lobes triangular ; flowers pink or purple. 

 Leaf-lobes linear-lanceolate to oblong. 

 Flowers yellow or cream-color. 

 Flowers purple. 



Outer bracts with spines of nearly or quite their length. 

 Leaves entire or undulate ; outer pappus-bristles barbellate. 



3. Leaves green both sides, somewhat pubescent beneath. 



Leaf-lobes acute ; bracts of the involucre faintly nerved ; roots solid. 1 1. C. odoratum. 



Leaf-lobes blunt ; bracts with prominent glutinous midnerve ; root hollow. 12. C. Hillii. 



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

 Heads large, few, i'-4' broad ; flowers all perfect and fertile. 



Heads involucrate by the upper very spiny leaves ; flowers usually yellow. 13. C. horndulum. 

 Heads peduncled, naked, or with i or 2 bracts at the base ; flowers purple. 

 Heads small, numerous, i' or less broad. 



Heads partly dioecious ; leaves not decurrent. 

 Heads not dioecious ; leaf-bases decurrent. 



6. C. undulatum. 



7. C. plattense. 



8. C. Flodmani. 



9. C. ochrocentrum. 

 10. C. nebraskense. 



14. C. muticum. 



15. C. arvense. 



1 6. C.palustre. 



