with a fifth one attached in an outer "series;" receptacle less than 1 mm. broad, 

 essentially flat, naked; ray flowers absent; disk flowers uniformly 4 per head, 

 perfect, fertile, the corolla whitish and 5-toothed terminally; achenes short- 

 columnar or slightly obconical, 5-ribbed; pappus persistent, of about 30 rather 

 stiff bristles. Incl. var. pubescens T. & G. 



Frequent in river bottoms and other moist woods, swampy backwaters, in Okla. 

 (Choctaw Co.) and e. and s.e. Tex., rare in Rio Grande Plains and n.cen. Tex., 

 late summer-fall; warmer parts of Am., n. to Sin., and to N.E. and s. Ont. 



5. Eupatorium L. Boneset. Thoroughwort 



Usually perennial herbs, also fairly commonly scandent elongate perennial 

 herbs, or a few species of shrubs; leaves opposite; heads often in roughly corymbi- 

 form aggregations either at the top of the plant or terminal on the branches; 

 involucre hemispheric or campanulate to essentially cylindrical; phyllaries more 

 than 4, in 2 to 6 series, either subequal (when few-seriate) or strongly imbricated, 

 usually with 1 or more vertical nerves, usually herbaceous (rarely papery) in 

 texture, occasionally somewhat indurate basally; receptacle flat to conic, naked; 

 ray flowers absent; disk flowers few to numerous, perfect, fertile, the corolla 

 equally 5-toothed terminally, whitish, bluish, purplish or roseate; style branches 

 long and clavate; achenes usually blackish, subcolumnar or gently narrowed to the 

 base, 5-ribbed (occasionally fainter intermediate stripes visible); pappus of slender 

 bristles, persistent. Conoclinium (L.) DC. 



Primarily an American genus of about 1,000 species, a few in Europe, Asia 

 and Africa. 



1. Leaves connate-perfoliate 1. E. perfoUatum. 



1. Leaves not connate-perfoliate (2) 



2(1). Most of the leaves whorled (3) 



2. Most of the leaves only opposite, not whorled (4) 



3(2). Stem deep-purple or purple-spotted, not glaucous; inflorescence or its 

 divisions flat-topped 2. E. maculatum. 



3. Stems glaucous, solid, green with purple only at the nodes; inflorescence with 



a rounded or convex summit 3. E. purpureum. 



4(2). Most of the leaves deeply palmately 3- to 5-lobed and the lobes again 

 pinnately dissected 8. E. Greggii. 



4. Most of the leaves unlobed (5) 



5(4). Receptacle conical; corollas blue (rarely white) (6) 



5. Receptacle fiat or essentially so; corollas white, pink or purple (7) 



6(5). Blades deltoid; stems scandent-climbing to 2 m. tall 4. E. coelestinum. 



6. Blades oblong, usually 2 to 3 times as long as broad, the lower corners often 



prolonged parallel to the petioles; stem not more than 1 m. tall, 

 much of it reclining and node-rooting 5. E. betonicifolium. 



7(5). Weedy subshrub of southern Arizona; involucres broadly campanulate, 

 about 4 mm. high; head about 25-flowered 7. E. pycnocephahim. 



7. Perennial herb of eastern Texas; involucre inverted-conical, about 7 mm. high; 



head about 5-fiowered 6. E. leucolepis. 



1. Eupatorium perfoliatum L. Thoroughwort. 



Rhizomatous perennial forming colonies; aerial stems (3-) 5-15 dm. tall, simple 

 below, branched in the upper part; leaves opposite, lanceolate, sessile, perfoliate, 

 (3-) 5-15 cm. long, serrate, softly pubescent especially on the underside; heads 

 numerous and crowded, 10- to 20-flowered; involucre obconic, 3-5 mm. high, 



1601 



