AND THE NEIGHBOURING DISTRICTS. 195 



The shores of the Rio de la Plata are characterized by many herbaceous Kelianthece : — 

 species of Leighia, Verbesina, Bidens, &c. The genera Vernonia, Baccharis and Eupato- 

 rium, so characteristic of tropical Brazil, extend into this region, but no longer in such 

 amazing numbers. At the Cape of Good Hope, where the abundance of Composites is 

 remarkable, the prevailing groups are for the most part different from those of Buenos 

 Ayres ; in particular, the Everlastings (ffelichrysece), so prodigiously numerous at the Cape, 

 are comparatively scarce in the corresponding latitudes of South America. The universal 

 genus Senecio, however, abounds in both countries. 



It has been observed, that the species of this family have not in general so wide a geo- 

 graphical range as might have been expected, considering the facilities for dissemination 

 afforded by their feathered seeds. Nevertheless, several of the Compositce of the Plata are 

 tropical species, and some even common to both hemispheres. Bidens helicmthoides, a 

 common marsh plant at Buenos Ayres, appears to be a native of Mexico, Guiana, and 

 Chile. Flaveria Contrayerba is common to Buenos Ayres (Mr. Pox), Peru, and Mexico. 

 Achyrocline fiaccida, common at Bio de Janeiro, was observed by Mr. Pox to range all 

 the way from that place to the north bank of the Plata, and was also found by Schom- 

 burgk in Guiana. Gnaphalium Gaudichaudianum, another native of Bio, is in Mr. Pox's 

 collection from Monte Video. Bterocaulon spicattim appears to have much the same range 

 as Achyrocline fiaccida : I have specimens from British Guiana, Rio de Janeiro, Rio Grande, 

 and Maldonado *. The first and last of these stations are separated by about thirty-seven 

 degrees of latitude. Baccharis trimera, P)eC, also appears to be widely diffused in South 

 America : it is one of the most common plants all the way from the gold district of Brazil 

 to the Serra da Estrella near Rio f ; it has been found at Bahia and at St. Catherine's ; 

 Mr. Pox met with it at Monte Video as well as in Rio Grande ; and it is probably the 

 same species that is mentioned by Sir "W. Hooker J as found by Dr. Gillies in the Pampas 

 of Buenos Ayres, and by Tweedie in Northern Patagonia. All these, however, are in- 

 stances of diffusion in latitude : I have not found among the Compositce of the Argentine 

 region (excluding evidently naturalized plants) any that are common to more than one 

 continent. 



Asclepiadece. — This order is numerous in Rio Grande and the Argentine region, as it 

 seems to be in South America generally, although these countries by no means rival the 

 Cape of Good Hope in the abundance of Asclepiads. One species, the Gomphocarpus fru- 

 ticosus, widely diffused over the warmer parts of the old world, occurs also, I believe, at 

 Monte Video ; at least the specimens gathered there appear to me undistinguishable from 

 the Cape plant ; but it may have been accidentally introduced to this locality. With the 

 exception of this genus and Cynanchmn, the Asclepiads of Rio Grande and the Plata all 

 belong to strictly American forms, among which Oocypetalum predominates in number. I 

 find in Mr. Pox's collection only one species of Asclepias {A. citrifolia ?) ; the A. Curas- 



* The specimens from Maldonado have narrower and more pointed leaves than the others, hut Sir W. Hooker 

 named them Pt . spicatum, without any indication of doubt. 



f It is certainly the B. genistelloid.es of Spix and Martius's ' Travels in Brazil.' Is it really distinct from the true 

 B. genistelloides ? 



X Journ. Bot. vol. hi. p. 42. 



2d2 



