AND THE NEIGHBOURING DISTRICTS. 195 
The shores of the Rio de la Plata are characterized by many herbaceous Heliantheg :— 
species of Leighia, Verbesina, Bidens, &c. The genera Vernonia, Baccharis and Bupato- 
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 Composite is 
. remarkable, the prevailing groups are for the most part different from those of Buenos 
Ayres ; in particular, the Everlastings (Helichryseæ), 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 Composite of the Plata are 
tropical species, and some even common to both hemispheres. Bidens helianthoides, 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. Fox), Peru, and Mexico. 
Achyrocline flaccida, common at Rio de Janeiro, was observed by Mr. Fox 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 Rio, is in Mr. Fox's 
collection from Monte Video. Pterocaulon spicatum appears to have much the same range 
as Achyrocline flaccida: I have specimens from British Guiana, Rio de J aneiro, Rio Grande, 
and Maldonado*. The first and last of these stations are separated by about thirty-seven 
degrees of latitude. Baccharis trimera, DeC., 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 +; it has been found at Bahia and at St. Catherine's; 
Mr. Fox 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 f 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 Composite of the Argentine 
region (excluding evidently naturalized plants) any that are common to more than one 
continent. 
Asclepiadeæ.—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 Cynanchum, the Asclepiads of Rio Grande and the Plata all 
belong to strictly American forms, among which Oxypetalum predominates in number. I 
find in Mr. Fox’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, but Sir W. Hooker 
named them Pt. spicatum, without any indication of doubt. ; 2. : E 
+ It is certainly the B. genistelloides of Spix and Martius's ‘Travels in Brazil.’ Is it really distinct from the true 
B. genistelloides ? 
Journ. Bot. vol. iii. p. 42. 
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