DISTRIBUTION OF TRIBES. 407 
any structural characters, and yet natural enough to be readily 
recognized :—1. The Antarctic and Australian genera Pleurophyl- 
lum and Celmisia, closely connected with the Andine secüon 
Oritrophium of Erigeron, differ from it chiefly in the shape of the 
achene, which is more that of Olearia, a genus bearing the same geo- 
graphical relation to Aster that Celmisia does to Erigeron, 2. The 
Hawaian Zetramolopium, an insular group of about half a dozen 
species, which during its long isolation has, like so many other 
insular forms, assumed more or less of a shrubby habit. In this 
respect it is still connected with Erigeron through the similarly 
insular (Juan Fernandez) Terranea above mentioned. As to 
structural characters, Tetramolopium has, on account of its subulate 
style-appendages, been connected by A. Gray with Vittadinia; but 
the latter genus appears to me to be further removed from Erigeron. 
A similar style is observable in the Andine section Oritropium of 
Erigeron. 3 &4. The small Asiatic extratropical genera Brachyactis 
and Lachnophyllum, the former with one species extending into 
North America, both nearly allied to Aster, Erigeron,and Conyza, 
the species bandied about from the one to the other, difficult tech- 
nically to distinguish from them, but with a peculiar habit justifying 
their maintenance as distinct genera, unless the three great types 
be reunited into a single one. 5. The Asiatic and African 
Microglossa, which, however, may be best considered, with its 
other relations, under the Conyza type. 
There are yet two genera connected with Aster and Erigeron, 
but rather more clearly distinguished on structural grounds, and 
to a certain degree supported geographically, both with elongated 
although still flattened achenes, with the pappus almost that of 
Aster, but with a habit more approaching Erigeron: one is Podo- 
coma, with five South-American and one Australian species in 
which the achene is attenuated into a beak, whilst the style is 
that of Aster, but the ligule more numerous, like those of the 
Aster-like Erigerons; the other, Vittadinia, has the flowers of 
Erigeron, or almost of Conyza, elongated but beakless achenes, the 
pappus nearly of Aster, and the subulate style-appendages of the 
section Oritropium of Erigeron ; and with these characters we find 
species scattered over South America and Australia, as in the case 
of Podocoma, but with the addition of one from the Sandwich 
Islands. 
There are, again, a number of small or monotypic genera ranging 
geographically around the Aster or Erigeron groups, which have 
