THISTLE FAMILY 231 



Ray-flowers neutral: paleae of the receptacle subulate, stiff, subtending only the 

 inner disk-flowers. 117. Mabuta. 



Receptacle naked or merely pubescent. 



HeaAs radiate; achenes 5-10-rlbbed aU around. 



Ligules white, flat, spreading, longer than the disk-corollas. 



119. Ledcanthemum. 

 Ligules yellow, concave, erect, not longer than the disk-flowers. 



120. Tanacetxjm. 

 Heads in ours discoid; achenes 2-5-rlbbed. 



Anthers obtuse. 



Heads soUtary, pedxmcled; flowers in our species aU alike (the ray-flowers 



found in other species lacking) . 118. Chamomilla. 



Heads in contracted panicles or glomerules, or in one species sohtary; flowers 



of two kinds, the marginal pistillate, but without Ugules. 



121. Sphaeromeria. 

 Anthers with pointed tips; heads racemose, rarely solitary; marginal pistillate 



flowers without ligules. 

 Plants spiny; achenes and corollas cobwebby. 122. Picrothamntjs. 



Plants not spiny; achenes not cobwebby. 123. Artemisia. 



Tribe 10. SENECIONBAE. 

 Plants scapiferous, dioecious or nearly so. with large ba-sal leaves appearing after flower- 

 ing; hermaphrodite flowers usually sterile. 124. Petasites. 

 Plants not scapiferous; not dioecious; disk-flowers hermaphrodite, fertile. 

 Involucres of many or several bracts. 



Involucres lax, of commonly much overlapping or unequal bracts, 

 Low annual herbs, with alternate leaves. 



Heads discoid; receptacle flat; corollas with very short tube. 



126. PSATYROTES. 



Heads radiate; receptacle conical; disk-flowers with long tube. 



125. Chocidium. 

 Suilrutescent perennial, with opposite leaves; heads radiate. 



127. Haploestes. 

 Involucres of connivent erect herbaceous equal bracts, with or without smaller 



calyculate ones below. 

 Leaves mostly opposite; pappus of a single series of rigid bristles. 



128. Arnica. 

 Leaves alternate; pappus of numerous soft bristles. 129. Senecio. 



Involucres of 4-6 firm concave erect and strongly overlappiQg bracts; shrubs witlj 

 alternate leaves and discoid heads. 130. Tetradymia. 



Tribe 11. CYNAREAE. 

 Achenes attached by the very base; flowers all alike oi nearly so; hermaphrodite. 

 Leaves not prickly; fllaments glabrous: style-branches slender, free. 



Involucre globose; bracts subulate, spine- or awn-llke, spreading, hooked at the 



tip. 131. Aectidm. 



Involucre oblong or obovoid; bracts appressed, muticous. 



132. Sausstjrea. 

 Leaves more or less prickly; fllaments bearded or papulose, rarely glabrous: style- 

 branches more o, less united into a cyhndrical body with a hair-ring below. 

 Receptacle densely bristly: pappus plumose. 133. Oirsium. 



Receptacle deeply honeycombed, scarcely bristly; pappus not plumose. 



134. Onopordon. 

 Achenes obliquely attached by one side; marginal flowers usually neutral, with enlarged 

 obUque corollas. 135. Centaurea. 



1. VERNONIA Schreb. Iron-weed. 



Leaves ovate-lanceolate, pinnately veined; bracts obtuse or acute. 1. V. corymbosa. 



Leaves Unear or lance-linear; lateral veins indistinct; bracts short-acimilnate. 



2. V. marginata. 



2. HOFMEISTERIA Walp. - l. H. pleunseta. 



3. EUPATORIUM L. Joe-pye Weed, Thoeoughwort, Boneset, White, 



Snake-root. 

 Leaves verticillate in whorls of 3's; flowers pink or rose-colored. 



Leaf-blades lanceolate, acuminate, strongly reticulate and rugose. 1. E. Bruneri. 

 Leaf-blades broadly ovate, acute, neither strongly reticulate nor rugose. 



2. E. maculaium. 

 Leaves opposite; flowers white or sUghtly tinged with pink, 



Achenes hispiduloiis on the angles. 



Bracts unequal in length, distulctly ribbed only towards the base. 



3. E. texense. 

 Bracts essentially equal in length, strongly ribbed to near the apex. 



4. E. arizonicum. 

 Achenes merely glandular-puberulent or glabrate. 5. E. occidentale. 



4. COLEOSANTHUS Cass. 



Leaf-blades ovate-cordate or deltoid. 



Leaves subsessile or short-petioled, ovate, veiny, spinulose-toothed, acuminate: 

 bracts flrm-chartaceous, 3-6 mm. wide. 1. C atractylotdes. 



