MONOPETALOUS EXOGENOUS PLANTS. 337 



BIGELOVIA, DC. 



Heads 3-4-flowerecl, the flowers all tubular and perfect; 

 involucre cylindrical-club-shaped, as long as the flowers; 

 the scales linear, rigid, appressed, somewhat viscid ; recep- 

 tacle narrow, cuspidate; achenia terete, striate, hairy; 

 pappus simple, of numerous scabrous capillary bristles ; 

 styles scarcely exserted. — A smooth erect perennial herl, 

 with narrow obtuse and entire leaves, and small heads of 

 yellow flowers, disposed in a compound corymb. 



B. NUDATA, DC. Stem mostly simple, virgate; lowest 

 leaves spatulate-lanceolate, obscurely 3-nerved, the others 

 scattered, linear. Stem 2° high. 



ISOPAPPUS, Torr. and Gray. 



Heads several-flowered; rays 5-12, pistillate; involucre 

 cylindrical-campanulate; the scales lanceolate-subulate, 

 imbricated in 2-3 rows, appressed ; receptacle alveolate ; 

 aclienia terete, silky; pappus a single row of nearly equal 

 capillary bristles. Biennials. Stems paniculate; leaves 

 alternate, narrow; heads scattered, on slender peduncles; 

 rays yellow. 



I. DiYAKiCATUS, Torr. and Gray. Hispid and glandu- 

 lar; stem, erect, the slender branches spreading; leaves 

 linear-lanceolate, sparingly toothed ; involucre soft-hairy ; 

 rays D-S. Stem l°-4° high; ^j^mc/e large; heads 15-20- 

 flowered. 



HETEROTHECA, Cass. 



Heads many-flowered ; rays pistillate ; scales of the 

 involucre imbricated in few rows, linear ; receptacle alveo- 

 late, bristly ; achenia of the rays oval, destitute of pappus, 

 those of the disk-flowers obovate, compressed, hairy, with 

 a double pappus, the outer one short and chafl'v, the inner 



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