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 loith a scarious, jayged, 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 nipper Tialf 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- 

 rent appendages; florets purple, the outer row radiant. — 



