DISTRIBUTION OF TRIBES. 448 
Amongst the epappose Verbesinew there are two small and 
very distinct genera which have a very wide tropical distribu- 
tion. Enhydra, with about a dozen species, is well represented in 
tropical Asia, Africa, and America, and has no near connexions 
in either country to indicate its origin, unless perhaps the 
Andine genus Aphanactis, two species, prove to be really allied 
toit. The most distinct species of Enhydra are also American; 
those of the Old World may be varieties of a single one. The 
other genus, Eclipta (three or four species), has likewise 
one cosmopolitan tropical species, to which the nearest allied 
local one is Australian; but beyond that there are no further 
connexions in the Old World. The remaining one or two 
species, forming a slightly distinct section, are in extratropical 
South Ameriea, where also is to be found the next nearest 
monotypic genus, Leptocarpha. 
Chrysanthellum is a small annual weed dispersed, under various 
names, over tropical Asia, Africa, and America, without affording 
any clue as to its original country, except the faint one supplied 
by a second species which has established itself in the Galapagos, 
tending to indicate an American origin. Affinities with other 
genera give no further assistance; for the nearest to it (though 
quite distinct from it) appear to be Heterospermum and Glosso- 
cardia, both monotypic, the one tropical-American, the other 
East-Indian. Synedrella, which is a nearer approach to the true 
Verbesinez, has two American species, of which one, like Zle- 
phantopus, is dispersed over tropical Africa and Asia. 
With regard to the Verbesinee strictly limited to America, the 
North-American genera take a great part, although not displaying 
any proportionate diversity of form except in the Mexican region. 
Rudbeckia, which, taken as a whole, is a natural and distinct 
genus of twenty-five species, is limited to North America and 
almost to the United-States region; so also are Balsamorhiza (ten 
species), Wyethia (four species), Helianthella (six species), all 
more or less diverging from Helianthus, but geographically rather 
more western. Tetragonotheca (three species) is likewise strictly 
North-American, but more distinct. Helianthus itself is by far 
the largest North-American Helianthoid genus; for about forty 
out of its fifty-two species are spread over that continent without 
having any special western character. It is, however, represented 
in Central and Southern America not only by a few species, which 
cannot well be generically distinguished from it, descending along 
