556 



i i i\in i i \k. 



Vol. 111. 



Corolla-tube slender, the limb expanded and deeply 5-cleft. Filaments pilose. Anthers sagit- 

 tate .11 the base. Achenes obovate or oblong, 4-angled or compressed, smooth or corrugated. 

 Pappus bristles in several series, filiform, barbellate or plumose, united at the base. [Greek, 

 Vsses' thistle, the ancient name.] 



About i-' species, natives oi the 1 Hd World, the following typical. 



1. Onopordon Acanthium L. Cotton 

 Thistle. Scotch Thistle. Fig. 4*155. 



Onopordon Acanthium L. Sp. PI. 827. 1753. 



Biennial, white-tomentose all over ; stem usually 

 much branched, leafy, 3-Q high. Leaves oblong, 

 lobed and dentate, acute, very spiny, the lower 

 often 12' long; heads 1Y-2' broad, about \V high, 

 solitary at the ends of the branches; outer bracts 

 of the involucre ovate or oblong, minutely serru- 

 ate, tipped with long stout spreading spines ; 

 flowers pale purple ; achenes slightly corrugated ; 

 pappus bristles brownish, longer than the achene. 



In waste places. Nova Scotia and Ontario to New 

 Jersey. Pennsylvania and Michigan. Naturalized 

 from Europe. Native also of Asia. Argentine. Asses', 

 oat or down-thistle. Queen Mary's-, silver- or musk- 

 thistle. July-Sept. 



108. CENTAUREA L. Sp. PI. 909. 1753. 



Perennial or annual herbs, with alternate entire dentate incised or pinnatifid leaves, and 

 large or middle-sized heads, of tubular purple violet white or rarely yellow flowers. Invo- 

 lucre ovoid or globose, its bracts imbricated in many series, appressed, fimbrillate, or dentate. 

 Receptacle flat, densely bristly. Marginal flowers usually neutral and larger than the central 

 ones, which are perfect and fertile, or flowers all perfect and fertile in some species. Corolla- 

 tube slender, the limb regular or oblique, 5-cleft or 5-lobed, the segments sometimes appearing 

 like rays. Anthers sagittate at the base. Style-branches short, somewhat connate, obtuse. 

 Achenes oblong or obovoid, compressed or obtusely 4-angled, usually smooth and shining, 

 obliquely or laterally attached to the receptacle, surmounted by a disk with an elevated mar- 

 gin. Pappus of several series of bristles or scales, rarely none. [Greek, of the Centaurs, 

 who were said to use it in healing.] 



About 350 species, mostly natives of the Old World. Type species: Centaurea Centaiirium L. 



Bracts of the involucre lacerate or fimbriate, not spiny. 



Heads 2' broad or less ; achenes laterally attached ; introduced species. 

 Annual ; leaves entire. 



Perennials or biennials, or C. maculosa annual. 

 Bracts of the involucre laciniate or entire. 

 Bracts of the involucre, or their tips, pectinate-fringed. 



Lower bracts of the involucre pectinate-fringed to below the middle 

 Leaves entire or merely dentate. 

 Leaves pinnatifid. 

 Lower bracts of the involucre pectinate-fringed only at the tips. 

 Leaves entire, toothed, or the lower lyrate. 

 All but the upper leaves pinnatifid into linear segments. 

 Heads 2'-^' broad ; achenes obliquely attached ; native western species. 

 Bracts of the involucre tipped with stout spines. 

 Flowers purple ; stem wingless. 



Flowers yellow ; stem winged by the decurrent leaf-bases. 

 Spines slender, purplish, 5" long or less, branched below. 

 Spines stout, yellow, 6"-io" long, with smaller ones at the base. 



