STANDLEY—ALLIONIACEAE OF THE UNITED STATES. 335 
The genus Allionia contains about 20 species besides those cited here. It is 
best represented in the western and southwestern parts of the United States 
and in Mexico; it extends into South America as far as Chile and Peru. It is 
a remarkable fact that one species, A. Wimalaica, extends into the Himalaya 
Mountains of Asia, the only species to be found outside the western hemisphere. 
A number of species occur in Mexico which are not included in this paper 
because of the inability of the author to secure reliable material of them. A 
considerable number of sheets of Mexican origin were seen which were referred 
by their collectors to A. violacea, A. glabrifolia, and similar species, but the 
author was unable to determine them satisfactorily, the only material in whose 
identity any confidence could be placed being that in the Bernhardi Herbarium. 
The various species, although they do not usually cover such wide ranges as 
the species of Boerhaavia, extend sometimes over rather large areas. Some 
species, such as A. hirsuta and A. nyctaginea, are found almost throughout 
the central-western part of the United States, while others, judging from the 
material now in the various herbaria, are confined to very small areas, areas as 
small as those occupied by species of Abronia. In this matter of the extent of 
distribution of individual species this genus stands midway between Abronia 
and Boerhaavia. 
Allionin can be at once divided into two natural sections, one with flowers 
whose perianths are crimson in color and have a conspicuous tube, and the 
other with flowers whose perianths are purplish, pink, white, or greenish, but 
never scarlet, and are campanulate in form,: It is possible that at some time 
the crimson-flowered species will be found worth separating as a new genus. 
They are so like the other species in habit and general appearance, however, 
that the writer has thought best to leave them in the genus Allionia. 
There is room for some interesting field work in this genus, especially in 
order to determine the relation of the forms with axillary infiorescence to those 
with panicled or cymose inflorescence. ‘The opinion has been expressed by 
various persons that some of the forms with axillary flowers may be merely 
depauperate or shade forms of species with more numerous flowers. A. aggre- 
gata bears a very striking resemblance to A. hirsuta, A. decumbens to A. lanec- 
olata, and A. bodini to A. linearis, Several other similar cases could be men- 
tioned. The possibility of A. aggregata and A. hirsuta being variations of the 
same plant is made more plausible by the fact that they occupy practically the 
same area of distribution; the same is true in the other two instances men- 
tioned. If it should be proved that one of. these pairs is related in the way 
suggested—that is, that the axillary-flowered plant is merely a form of another 
larger plant induced by peculiar environmental conditions—then such plants as 
A. decumbens, A. aggregata, and others should, of course, take the rank of 
subspecies of the species to which they are most closely related. There are a 
few of the forms with axillary involucres which do not seem to be closely 
related to other more complex forms, but perhaps this is because the plants to 
which they are related have not yet been collected. 
KEY TO THE SPECIES. 
Perianth scarlet, with a conspicuous tube; leaves linear. 
Plants sparingly branched, tall and erect; involucres 
8-fruited; flowers not cleistogamous__ ~~ ~------~-- 1. A. coceinea. 
Plants diffusely branched, lower; involucres mostly 
1-fruited; flowers usually cleistogamous; plants 
more slender. 
