316 CICHOEIACEAE. 



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1. L. Scariola L. Stem nearly or quite glabrous, 4-15 dm. tall: leaf-blades 

 oblong to lanceolate in outline, pinnatifid, bright- green : inner bracts of the 

 involucre 8-10 mm. long, linear-oblong: outer corollas 8-9 mm. long: achene- 

 body abruptly narrowed at the apex. S. Bare, on roadsides. Nat. of Eu. 

 PRICKLY-LETTUCE. 



2. L. virosa L. Stem hirsute below, 6-20 dm. tall: leaf -blades oblanceolate 

 to oblong, merely denticulate, glaucous: inner bracts of the involucre 12-15 

 mm. long, narrowly linear: outer corollas 11-12 mm. long: achene-body gradu- 

 ally narrowed at the apex. Eather common, in waste places and on road- 

 sides. Nat. of Eu. 



3. L. sagittifolia Ell. Stems 9-30 dm. tall, glabrous: blades of the stem- 

 leaves 8-30 cm. long, irregularly dentate: involucres 10-20 mm. long, the 

 inner bracts narrowly linear or nearly so: ligules yellow or reddish: achene- 

 body 2.5-3 mm. long, longer than the beak. Susquehanna valley. Frequent, 

 on shaded banks. 



4. L. canadensis L. Stems 9-30 dm. tall, glabrous or nearly so: blades of 

 the stem-leaves 10-30 cm. long, sinuate-pinnatifid : involucres 10-12 mm. long, 

 the inner ones linear-lanceolate: ligules yellow: achene-body 3-4 mm. long, 

 about as long as the beak. Common, in fields and on roadsides. WILD- 

 LETTUCE. HORSE-WEED. 



5. MULGEDIUM Cass. Herbs resembling Lactuca in habit. Achenes 

 thick, beakless. Sum. and fall. LETTUCE. BLUE-LETTUCE. 



Pappus bright-white : blades of the stem-leaves neither auriculate nor clasping. 



Leaf-blades toothed : achene-body not narrowed into a neck. 1. M . villosum. 



Leaf-blades pinnatifld : achene-body narrowed into a slender 



neck. 2. M. floridanum. 



Pappus brown : blades of the stem-leaves auriculate and clasping. 3. M. spicatum. 



1. M. villosum (Jacq.) Small. Stems 9-20 dm. tall: blades of the stem-leaves 

 irregularly dentate, 8-20 cm. long: inner bracts of the involucre linear-lanceo- 

 late: ligules blue: achenes 4 mm. long. N. Frequent, in open woods and 

 thickets. Sandstones and shales. 



'2. M. floridanum (L.) DC. Stems 10-30 dm. tall: blades of the stem-leaves 

 lyrate-pinnatifid, 2^5 cm. long: inner bracts of the involucre linear: ligules 

 blue : achenes 6-7 mm. long. Common, in thickets and on banks. 



3. M. spicatum (Lam.) Small. Stems 9-35 dm. tall: blades of the stem-leaves 

 lobed or pinnatifid (merely denticulate in M. spicatum integri folium) : ligules 

 white, yellowish, or bluish: achenes 4-5 mm. long. Eather common, in 

 thickets and open woods. 



6. SONCHUS [Tourn.] L. Annual or perennial tall caulescent herbs. 

 Leaf -blades entire, toothed, or pinnatifid, sometimes spiny margined. Heads 

 erect. Involucres ovoid or subglobose. Achenes flattened. Pappus deciduous. 

 Spr.-f all. SOW-THISTLE. 



Leaf-auricles rounded : achenes smooth and 3-ribbed. 1. 8. asper. 



Leaf-auricles acute : achenes transverse-wrinkled and striate. 2. 8. oleraceus. 



1. S. asper (L.) All. Stems 2-15 dm. tall: leaf -blades with rigid-tipped 

 teeth: achenes 2-2.5 mm. long, margined, ribbed and smooth. N. M. Com- 

 mon, in fields and on roadsides. Nat. of Eu. 



2. S. oleraceus L. Stems 1-18 dm. tall: leaf -blades more divided than in 



5. asper, with soft-tipped teeth: achenes 2.5-3 mm. long, scarcely margined,, 

 striate and transverse-wrinkled. Common, in waste places and fields. Nat- 

 of Eu. 



