COMPOSITAE. IO3I 



a. Leaves tomentose on oth sides, or becoming glabrous above; western. 

 Leaves pinnately parted; segments linear, entire or lobed. 6. 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. 7. C. undulatus. 



Leaf-lobes linear-lanceolate to oblong ; flowers cream-color. 



8. C. Plattensis. 



Outer bracts with spines of nearly or quite their length. 9. C. ochrocentrus. 



Leaves entire or undulate; outer pappus-bristles barbellate. 10. C. Nebraskensis. 



3. Leaves green both sides, somewhat pubescent beneath. 



Leaf-lobes acute; bracts of the involucre faintly nerved. n. C. odoratus. 



Leaf-lobes blunt ; bracts with a prominent glutinous midnerve. 12. C. Hillii, 



f f 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. 



13. C. spinosissimus. 

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



14. C. muticus. 

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



15. C. arvensis. 

 * * Pappus-bristles simple, or minutely serrulate. (Plumeless Thistles.) 



Head solitary, nodding; bracts of the involucre lanceolate. 16. C. nutans. 



Heads clustered, erect or ascending; bracts linear 17. C. crispus. 



1. Carduus lanceolatus L. COMMON BUR OR SPEAR THISTLE. (I. F. 

 f. 4058.) Biennial; stem stout, branched, more or less tomentose, 11.5 m> high, 

 leafy to the heads. Leaves dark green, lanceolate, acuminate, deeply pinnatifid, 

 7-15 cm. long, or the lowest larger, decurrent on the stem and branches, the 

 lobes triangular-lanceolate, tipped with stout prickles, the margins and decurrent 

 bases bristly, the lower surface brown-tomentose and midnerve pilose especially 

 when young; heads mostly solitary at the ends of the branches, 4-5 cm. broad, 

 4-5 cm. high; bracts of the involucre cottony, narrowly lanceolate, acuminate; 

 flowers dark purple. In fields and waste places, Newf. to Ga., west to Minn., 

 Neb. and Kans. Nat. from Europe. Native also of Asia. 



2. Carduus altissimus L. TALL OR ROADSIDE THISTLE. (I. F. f. 4059.) 

 Biennial or perennial; roots often thickened; stem pubescent, or tomentose, stout, 

 branched, leafy to the heads, 1-3 m. high. Leaves ovate-oblong or oblong-lanceo- 

 late, sessile, or slightly clasping, sparingly pubescent above, densely white-tomen- 

 tose beneath, scarcely or not at all decurrent, acute, spinulose-margined, entire, 

 dentate with bristle-pointed teeth or lobed, sometimes pinnatifid, the lowest some- 

 times 2 dm. long, narrowed into margined petioles, the uppermost linear or lanceo- 

 late, much smaller; heads about 5 cm. broad, 4-5 cm. high, mostly solitary at the 

 ends of the branches; outer bracts of the involucre ovate or ovate-lanceolate, 

 firm, with a dark, slightly glandular spot at the apex, tipped with short prickles; 

 flowers light purple. In fields and thickets, Mass, to S. Dak., Fla., Neb. and Tex. 

 Aug. -Sept. 



3. Carduus Flodmanii Rydb. FLODMAN'S THISTLE. Stem rather slender, 

 .5-1 m. high, more or less white cottony. Leaves deeply divided into linear-oblong 

 01 lanceolate, acute segments, floccose but green above, white-tomentose beneath; 

 head campanulate, 3-4 cm. broad; bracts like those of the preceding but nar- 

 rower; flowers rose or reddish purple. In river-bottoms and meadows, Neb. to 

 Mont, and Wyo. July-Sept. 



4. Carduus discolor (Muhl.) Nutt, FIELD THISTLE. (L F. f. 4060.) Simi- 

 lar to Cardnus altissimus, but lower and more leafy, seldom over 2 m. high. 

 Leaves deeply pinnatifid into linear, linear-lanceolate, or falcate, prickly-toothed 

 segments, white-tomentose beneath, sessile, the basal ones sometimes 3 dm. long; 

 heads 4-5 cm. broad, about 4 cm. high, usually involucrate by the upper leaves, 

 mostly solitary at the ends of the branches; outer bracts of the involucre coriaceous, 

 ovate, slightly woolly, tipped with, slender bristles, which are longer than those of 

 C. altissimus ; flowers light purple or pink, rarely white. In fields and along 

 roadsides, Quebec and Ont. to Ga., S. Dak., Neb. and Mo. July-Nov. 



5. Carduus Virginianus L. VIRGINIA THISTLE. (I. F. f. 4061.) Biennial; 

 stem slender, naked or scaly above, pubescent or somewhat tomentose, simple or 

 branched, 6-12 dm. high. Leaves oblong, oblong-lanceolate, or the lowest slightly 



