SPECIES AND VARIETIES. 379 



base and somewhat clasping; heads small, lateral and ter- 

 minal, hemispherical, with very short rays; florets yellow. 

 Moist sandy heaths. Fl. August, September. 



(34) Onopordum. 



O. Acanthium : biennial ; stem erect, many-headed, 4-5 

 feet high, woolly, with broad spinous wings, branched ; leaves 

 elliptic-oblong, woolly on both sides, sinuate, spiny, decur- 

 rent ; involucre nearly globose, large, somewhat cottony, the 

 scales fringed with minute spinous teeth ; florets purple. 

 Cotton Thistle. Waste ground. Fl. August, September. 



(35) Centaurea. 



* Involucral scales with a scarious, jagged, or pectinated, not 

 decurrent appendage. 



C. nigra : stem 1-2 feet high ; leaves scabrous, lanceolate, 

 sinuate-dentate, the upper entire or nearly so, stem-clasping ; 

 heads usually not radiant ; florets all fertile, purple or rarely 

 white ; involucre globular, nearly black externally, the appen- 

 dages of the outermost scales smaller and narrower than the 

 others, those of the innermost row roundish, dark brown, 

 membranous, jagged, all contracted just below the appendage. 

 Knapweed. Pastures and roadsides. Fl. June to September. 



** Involucral scales lanceolate, their upper half with a sca- 

 rious fringed decurrent margin. 



C. Scabiosa : stem 2-3 feet high, rough, furrowed ; leaves 

 hispid, pinnatifid, roughish, the segments lobed, with callous 

 points, the lobes of the upper ones entire; heads on long, 

 naked stalks, solitary; involucres rather woolly, the scales 

 pale, blunt, with dark acute membranous pectinated decur- 

 reiit appendages; florets purple, the outer row radiant. 



