COMPOSITAE. IO35 



none. [Greek, of the Centaurs, who ~ere said to use it in healing.] About 350 

 species, mostly natives of the Old World. Besides the following, 2 others, intro- 

 duced species, occur on the Pacific Coast, and are rarely found in ballast about the 

 eastern seaports. 



Bracts of the involucre lacerate or fimbriate, not spiny. 



Heads 4 cm. broad or less; achenes laterally attached; introduced species. 



Annual; pappus about the length of the achene. 1. C. Cyanus. 



Perennials ; pappus obsolete, or short. 



Flowers all perfect; marginal ones scarcely enlarged. 2. C. nigra. 



Marginal flowers neutral, with palmately cleft corollas. 3. C.Jacea. 

 Heads 5-10 cm. broad; achenes obliquely attached; native western species. 



4. C. Americana. 

 Bracts of the involucre tipped with stout, nearly simple spines. 5. C. Calcitrapa. 



i. Centaurea Cyanus L. Bluebottle. Corn Blue-bottle. Corn- 

 flower. (I. F. f. 4076.) Annual, woolly ortomentose, at least when young; stem 

 leafy, slender, branched, 3-7 dm. high, the branches ascending. Leaves linear or 

 linear-lanceolate, mucronate, 7— 15 cm. long, the basal and lower ones mostly den- 

 tate or pinnatifid, the upper or sometimes all of them, entire; heads on long naked 

 peduncles; involucre campanulate, its bracts greenish-yellow or with darker tips 

 and margins, appressed; flowers blue or purplish, varying to white, the marginal 

 ones neutral with large radiant corolla-limbs; achenes slightly compressed, or 4- 

 angled; pappus bristles unequal, nearly as long as the achene. In waste places, 

 escaped from gardens, and in ballast, Quebec to N. Y., Va., S. Dak. and Kans. 

 July-Sept. 



2. Centaurea nigra L. Black Knapweed. Horse-knops. Hardheads. 

 Centaury. (I. F. f. 4077.) Perennial, scabrous or pubescent; stem stiff, branched, 

 3-6 dm. high. Lower and basal leaves spatulate or oblong, acutish, entire den- 

 ticulate, dentate or lobed, not pinnatifid, 7-15 cm. long, narrowed into long peti- 

 oles; upper leaves oblong or lanceolate, sessile, or partly clasping, entire or nearly 

 so; heads rarely 2.5 cm. broad, bracted by the small, uppermost leaves; involucre 

 globose, its bracts lanceolate, or ovate-lanceolate, closely imbricated, tipped with 

 brown fimbriate appendages, or the uppermost merely lacerate; flowers rose-purple; 

 achenes slightly 4-sided; pappus none, or a ring of minute scales. In waste places 

 and fields, Newf. to Ont. and N. J. Nat. from Europe. July-Sept. 



3. Centaurea Jacea L» Brown or Rayed Knapweed. (I. F. f. 4078.) 

 Perennial, similar to the preceding species. Leaves entire or denticulate, rarely 

 lobed; heads 2.5-4 cm. broad; involucre globular to ovoid, its bracts closely im- 

 bricated, brown or with brown bracts, the outer ones with fimbriate appendages, 

 the middle ones lacerate, the inner entire or nearly so; achenes obscurely 4-sided; 

 pappus none, or a minute crown. In waste places, N. Y. to Conn, and Vt. and in 

 ballast about eastern seaports. Also in Br. Col. Fugitive from Europe. June- 

 Sept. 



4. Centaurea Americana Nutt. American Star Thistle. (I. F. f. 4079.) 

 Annual, roughish; stem stout, simple, or little branched, 6-18 dm. high. Leaves 

 entire or denticulate, the lower and basal ones spatulate or oblong, 5-12 cm. long, 

 narrowed into petioles, the upper oblong- lanceolate, sessile, mucronate; heads 

 solitary at the ends of the leafy stem or branches; involucre nearly hemispheric, its 

 bracts ovate or lanceolate with conspicuously pectinate appendages; flowers pink or 

 purple, the marginal ones with enlarged and radiant corolla-limbs; achenes some- 

 what compressed; pappus of copious unequal bristles longer than the achene. Dry 

 plains Mo. and Ark. to La., Mex. and Ariz. May-Aug. 



5. Centaurea Calcitrapa L. Star Thistle. (I. F. f. 4080.) Annual, 

 pubescent or glabrous, green; stem much branched, 3-4 dm. high. Leaves 1-2- 

 pinnatifid into oblong-lanceolate to linear, serrulate pinulose, dentate or entire 

 mostly acute lobes, the upper sessile and slightly clasping, the lower and basal 

 shwrt-petioled. 1-2 dm. long, the uppermost somewhat involucrate at the bases of 

 the sessile heads, which are about 25 mm. broad; involucre ovoid, its outer bracts 

 ovate-oblong, spiny ; flowers purple, none of them radiant; achenes compressed or 

 obscurely 4 sided; pappus none. In waste places and ballast, Mass. to N. Y., N. J. 

 and Va. Also in Br. Col Adventive or nat. from Europe. June-Oct. 



