ROBINSON AND GREENMAN. — GENUS VERBESINA. 635 



Cent.-Ara. Bot, are enumerated, with synonymy and citation of specimens, 

 30 named species known to grow in Mexico and Central America. So 

 rapid, however, has been the recent exploration of the regions mentioned 

 that this number is already more than doubled. 



The genus is now generally conceded to be exclusively American, 

 except so far as species have been introduced or naturalized in some 

 parts of the Old World. Various obscure gerontogeous plants, early 

 ascribed to Verhesina and enumerated in the Index Kewensis, are 

 omitted from the following revision as they are with little doubt generi- 

 cally distinct. 



The genus as here presented contains 109 species. More than 70% of 

 these are local, and over 90 % are confined to some one of the following 

 regions. 



S. E. United States (S. Car. to Fla. and Ala.) ... 3 species. 



Region of the Lower Rio Grande 2 " 



Sonoran Region (W. Tex. to L. Calif, and N. W. Mex.) 16 " 



Central and S. Mexico 44 " 



Central America 9 " 



N. South America (U. S. Colombia to Guiana) ... 4 " 



Brazil, Uruguay, Paraguay, Argentine Rep. . . . 11 " 



Andean Region (Ecuador to Chili) 8 " 



W. Indies 2 " 



Verhesina, as a whole, reaches its highest specific diversity in the 

 uplands of Central and Southern Mexico, where no less than 40% of its 

 species are endemic. The genus is conveniently divided into 1 2 sections, 

 of which HamuUum, Platyptera, Stenocarpha, Alatqjes, Pteropliyton, 

 Sonoricola, Ximenesia, and Pseudomontatioa are obviously natural 

 groups. Of these Hamulmm, Platyptera, Stenocarpha, Alatipes, and 

 Sonoricola are each composed of species of uniform or contiguous ranges. 

 Pseudomontanoa, apparently unrepresented in Central America and 

 "W. Indies, is found in Mexico and Caribbean S. America. Ximenesia 

 exhibits in the species V. australis a new instance of the interesting 

 community of character between the flora of the Rio Grande region and 

 that of extra-tropical S. America. 



The sections Verbeslnaria, Saubinetia, Ochractinia, and especially 

 Ltpactmia, must be regarded rather as provisional aggregates than 

 natural or wholly satisfactory groups. In the general arrangement of 

 the sections the sequence is from the large-headed to the small-headed 

 forms. It may be noted that discoid heads occur only in Platyptera and 



