GENUS 104. 



THISTLE FAMILY. 



55' 



7. Cirsium plattense (Rydb.) Britton. 

 Prairie Thistle. Fig. 4642. 



Carduus plattensis Rydberg, Contr. Nat. Herb. 3: 167. 

 pi. 2. 1895. 



Perennial or biennial, the root thick and deep; 

 stem stout, simple, or little branched, i*-2j tall, 

 densely white-felted. Leaves deeply pinnatifid, 

 white-tomentose beneath, green, loosely tomen- 

 tose, or glabrate above, the lower $'-?' long, the 

 lobes lanceolate to oblong, acute, prickly tipped 

 and margined ; upper leaves smaller and less di- 

 vided; heads few, about 2' high and broad; outer 

 bracts of the involucre lanceolate to ovate-lanceo- 

 late, firm, dark, tipped with a short weak spread- 

 ing prickle, the inner linear-lanceolate, unarmed, 

 tipped with a scarious reflexed erose appendage; 

 corolla yellow, its lobes linear; pappus of outer 

 flowers merely barbellate. 



Sand hills, Nebraska, Colorado and South Dakota. 

 May-July. 



8. Cirsium Flodmani (Rydb.) Britton. Flod- 

 man's Thistle. Fig. 4643. 



Carduus Flodmani Rydb. Mem. N. Y. Bot. Card, i: 451. 

 1900. 



Stem rather slender, ii-3 tall, loosely white-cottony, 

 usually more or less branched. Leaves deeply pinnatifid 

 into linear-oblong or lanceolate, acute or acuminate, 

 toothed or entire segments, floccose and green above, 

 densely white-cottony beneath, the lower 6' long or less ; 

 heads i$'-2 r broad ; involucre campanulate, its linear 

 bracts tipped with yellow prickles; flowers reddish- 

 purple to rose. 



Meadows and river bottoms. Iowa and North Dakota to 

 Saskatchewan, Nebraska and Colorado. Has been referred 

 to the western C. canescens. July-Sept. 



9. Cirsium ochrocentrum A. Gray. 

 Yellow-spined Thistle. Fig. 4644. 



Cirsium ochrocentrum A. Gray, Mem. Am. Acad. 



i : 1 10. 1840. 

 Ciiicus ochroccntrus A. Gray, Proc. Am. Acad. 19: 



57- '883. 

 Carduus ochroccntrus Greene, Proc. Phil. Acad. 



1892: 336. 1893. 



Similar to Cirsium undulatum, but commonly 

 taller and more leafy, often 6 high, equally 

 white-tomentose. Leaves oblong-lanceolate in 

 outline, usually very deeply pinnatifid into tri- 

 angular-lanceolate, serrate or entire segments, 

 armed with numerous long yellow prickles ; 

 lower leaves often 6'-8' long; heads about 2' 

 broad, \\'-2.' high, solitary at the ends of the 

 branches ; outer bracts of the involucre lan- 

 ceolate; tipped with stout yellow prickles of 

 nearly or quite their own length, the inner nar- 

 rowly lanceolate, long-acuminate; flowers pur- 

 ple (rarely white?). 



On plains, Nebraska to Texas, Nevada and Ari- 

 zona. May-Sept. 



