COMPOSITAE. 



2. 



[Vol,. III. 



Black Knap- 

 Hardheads. 



4077.) 



i/53- 



Centaurea nigra L,. 

 weed. Horse-knops. 

 Centaury. (Fig. 



Cenlaurea nigra L. Sp. PI. 911. 



Perennial, scabrous or pubescent; stem stiff, 

 branched, i-2 high. Lower and basal leaves 

 spatulate or oblong, acutish, entire, denticulate, 

 dentate or lobed, not pinnatifid, 3 / -6 / long, nar- 

 rowed into long petioles; upper leaves oblong or 

 lanceolate, sessile, or partly clasping, entire or 

 nearly so; heads rarely \ r broad, bracted by the 

 small, uppermost leaves; involucre globose, its- 

 bracts lanceolate or ovate-lanceolate, closely im- 

 bricated, tipped with brown fimbriate append- 

 ages, or the uppermost merely lacerate; flowers 

 rose-purple, all perfect, the marginal ones usu- 

 ally notatall enlarged; achenes slightly 4-sided; 

 pappus none, or a ring of minute scales. 



In waste places and fields, Newfoundland to On- 

 tario and New Jersey. Naturalized from Europe. 

 Among many other English names are Iron-head 



or -weed, Club-weed, Matfelon, Hurt-sickle, Tassel, Horse-knobs, Crop-, Knob-, Bole-, or Button-weed, 



Loggerheads, Lady's Cushion, Blue-tops. July-Sept. 



3. Centaurea Jacea L. Brown or 

 Rayed Knapweed. (Fig. 4078.) 

 Centaurea Jacea L. Sp. PI. 914. 1753. 



Perennial, similar to the preceding species. 

 Leaves entire or denticulate, rarely lobed; heads 

 x'-iYz' broad; involucre globular to ovoid, its 

 bracts closely imbricated, brown or with brown 

 backs, the outer ones with fimbriate appendages, 

 the middle ones lacerate, the inner entire or 

 nearly so; marginal flowers neutral with en- 

 larged radiant corolla-limbs; achenes obscurely 

 4-sided; pappus none, or a minute crown. 



In waste places northern New York and Vermont, 

 and in ballast about eastern seaports. Also in Brit- 

 ish Columbia. Fugitive from Europe. June-Sept. 



4. Centaurea Americana Nutt. 

 American Star Thistle. (Fig. 4079.) 



C. Americana Nutt. Journ. Phila. Acad. 2: 117. 1821. 

 Plectocephalus Americanus Don, in Sweet, Brit. 



Fl. Card. (II). pi. 51. 1831. 



Annual, roughish; stem stout, simple, or little 

 branched, 2-6 high. Leaves entire or dentic- 

 ulate, the lower and basal ones spatulate or ob- 

 long, 2 / -5 / long, narrowed into petioles, the 

 upper oblong-lanceolate, sessile, mucronate; 

 heads solitary at the ends of the leafy stem or 

 branches, very showy, 2 / -4 / broad; involucre 

 nearly hemispheric, its bracts ovate or lanceo- 

 late with conspicuously pectinate appendages; 

 flowers pink or purple, the marginal ones with 

 enlarged and radiant corolla-limbs; achenes 

 somewhat compressed, obliquely attached at 



the base; pappus of copious unequal bristles longer than the achene. 

 Dry plains, Missouri and Arkansas to Louisiana, Mexico'and Arizona. 



Ma5'-Aug. 



