OBSERVATIONS ON THE COMPOSITA. 18 
An interesting far western plant which can ill be associated 
with the species of any recognized genus I name 
Petradoria pumila. Chrysoma pumila, Nutt. Trans. 
Am. Phil. Soe. vii. 325 (1840). Solidago pumila, Torr. & 
Gray. Fl. ii. 210 (1842). Aster pumilus, O. Ktze. 1. c. 319. 
Genus distinguished from Huthamia by its woody caudex 
and cylindric glabrous distinctly 10-striate achenes; and from 
Chrysoma by the same characters and by its flat-topped 
corymbose inflorescence. The species is strictly montane in 
its habitat, and occupies apparently a narrow belt running 
almost diagonally across the western part of the North 
American continent, from Texas to Oregon. It is found only 
in very stony ground or on bleak ledges. The Greek word 
for a rock combines with Doria, an early name for the 
Goldenrod, to designate suitably the genus. 
There is a very natural group of species belonging to the 
mountains of Mexico and Central America, of which 
DeCandolle’s Aplopappus? stoloniferus is the type, which 
wear so exactly the appearance of Hrigeron, especially of the 
Japanese H. Thunbergi and the Californian L. glaucus, that I 
not long since published one of them under the name of 
EH. Heleniastrum. But having now been privileged to 
examine at Kew, a good series of specimens, I find it neces- 
sary to abandon that opinion; not because the typical species 
looks less like true Hrigeron, but because all exhibit certain 
characters of receptacle and achenes which are at variance 
with those of that genus as hitherto accepted. The achenes 
are apparently terete, quite pronouncedly silky, and are sur- 
mounted by a pappus rather too firm and too copious for 
Erigeron; and the receptacle is deeply alveolate. On these 
three or four technical characters, along with the external 
marks of Hrigeron with yellow rays, these plants must needs 
be separated from that genus and from Aplopappus; and I 
assign the group the generic name 
