TARAXACUM COMPOSITAE 403 



LACTUCA 



110 TARAXACUM Haller Stirp. Helv. i, 23. 



Acaulescent perennial herbs with rosulate leaves, naked scapes 

 that elongate in fruit, and mostly large heads of yellow flowers. 

 Heads many-flowered, usually solitary at the summit of the sim- 

 ple hollow scapes. Involucre a single series of nearly equal nar- 

 row bracts that are slightly united at base, and several or numer- 

 ous calyculate ones. Receptacle flat, naked. Achenes oblong- 

 ovate or fusiform, 4-5-costate or angled, and usually with some 

 intervening nerves, muricate or spinulose, at least near the sum- 

 mit which is abruptly contracted into a filiform beak. Pappus 

 soft and capillary, dull white. 



T. OFFICINALE Webber Prim. PL Hoist. 56. Scapes and leaves from the 

 crown of a thick vertical root : leaves from spatulate-oblong to lanceolate 

 in outline, and from irregularly dentate to runcinate pinnatifid, 3-10 inches 

 long: bracts of the involucre linear-lanceolate, not glaucous, the outer re- 

 flexed, all acute : achenes greenish-brown, fusiform, squamulose toward 

 the summit, abruptly contracted into a conical apex which is prolonged 

 into a filiform beak 2 or 3 times as long as the achene. Common in fields 

 and waste places. Naturalized from Europe. 



Ill RAFINESQUIA Nutt. Trans. Am. Phil. Soc. vii, 429. 



Leafy-stemmed annuals with pinnatifid leaves and rather large 

 heads of white or flesh-colored flowers terminating the paniculate 

 branches. Heads 15-30 flowered. Involucre conical or cylindra- 

 ceous, of 7-15 equal linear attenuate principal bracts and some 

 loose calyculate ones. Receptacle flat and naked. Achenes terete, 

 somewhat fusiform, obscurely few-ribbed, attenuate into a slender 

 beak, the broad base hollowed but not callous-thickened at the 

 insertion. Pappus of 10-15 capillary bristles, softly long-plumose 

 from the base to near the tip. 



R. Califomica Nutt. 1. c. Glabrous throughout: stem stout, much 

 branched, 2-3 feet high: leaves oblong; the lower 4-6 inches long; the up- 

 per gradually reduced to small bracts : involucre becoming thick at base 

 and more or less conical; its rather numerous calyculate bracts subulate 

 and spreading : ligules short, white : achenes tapering into a very slender 

 beak as long as the body: pappus dull white, the bristles fine and soft. 

 Shady ground, eastern Oregon to California. 



112 LACTUCA Tourn. Inst. t. 267. L. Gen. n. 909. 



Tall herbs with alternate leaves and small panicled heads of 

 yellow, white or blue flowers. Involucre cylindric, several to 

 many-flowered, either calyculate or more regularly imbricated. 

 Receptacle flat, naked. Achenes flat, 3-5-ribbed on each face, 

 narrowed above, or contracted into a narrow beak, which is more 

 or less expanded at the summit into a small disk that bears the 

 copious white or brownish pappus bristles which fall separately. 



§ 1 ScARioLA DC. Prodr. vii, 133. Achenes very flat, orbic- 

 ular to oblong, abruptly produced into a filiform beak which 

 bears the soft white pappus on its dilated apex. 



