STANDLEY—ALLIONIACEAE OF THE UNITED STATES, 8307 
corolla-like, with an elongated tube which is constricted above the ovary, 
expanding above into a 5-lobed limb; stamens 3 to 5, included, their filaments 
unequal; fruit leathery, usually 3 to S-winged but sometimes only ribbed or 
almost smooth: seed filling the pericarp, to which it adheres; one of the coty- 
ledons abortive, the seedling thus appearing monocotyledonous, 
Of the history of this genus Doctor Rydberg says: “tn the original publi- 
cation no type species was mentioned. The genus was described from a plant 
collected on Dé la Pérouse’s journey in California and cultivated by Mr. 
Colignon. Hooker, in his Exotic Flora,’ identifies Colignon’s plant as A broenia 
umbellata. The type of Tricratus is the same.” 
The genus is a North American one and is confined chiefly to the western 
part of the United States. One or two species extend into southwestern 
Canada and three into northwestern and northeastern Mexico, On the east 
the range extends into western Nebraska and IKkansas, and on the west to the 
acifie const. The writer has seen no specimens from southern central Arizona, 
where the genus would be expected to occur, since it is conmon to the east in 
southern New Mexico and to the west in California, but Prof. J. J. Thornber 
states that it is represented in that part of the Territory by one or more species. 
Most if not all the species seem to be in a yariable or mutating state. They 
are rather numerous and most of them are confined to comparatively small 
areas. One of the most striking illustrations of the latter fact is found in 
A. carletoni, the type of which was collected about sixteen years ago in eastern 
Colorado. but which, as far as the writer is able to learn, has never been col- 
lected since. Its closest ally has not been collected nearer than 350 miles to the 
south. 
The writer has tried, but with little success, to arrange the species in a lineal 
sequence, There are so many different lines along which different species vary 
that it is almost, if not quite, impossible to do this. There are several groups 
of species, for instance, which are closely related to .t. fragrans; but these 
groups vary in different directions so that it is impracticable to arrange them 
in a lineal succession which will show their closest relationships. This is true 
of sections as well as of species and applies equally to the other large genera such 
as Allionia nnd Boerhaavia. It is also difficult to arrange the species in sections, 
and the arrangement which is given here is not at all satisfactory on account 
of the many intergradient species. The maritinut and latifolia groups are dis- 
tinct enough. The fragrans and turbinata groups are most difficult of separa- 
tion on account of such forms as A. carlefoni and uA. nealleyi, either of which 
is as closely related to A. fragrans as to 1. turbinata, The nana group is 
easiest to separate because of the peculiar habit of the plants, a habit with 
which other peculiar characteristics are concurrent. 
Among the various characters which are of use in separating species of 
Abronia the habit is of importance, especially in the turbinata group. This is 
a character that is not well shown in dried specimens generally, for in such 
specimens it is difficult to tell whether a stem is erect, ascending, or prostrate. 
The pubescence is variable, but not nearly so much so as in the genus Boer- 
haavia. While the leaves upon a single plant are usually of the same general 
shape, the earlier ones commonly differ somewhat from the later, especially in 
size, It is worthy of note that in all the Abronias the opposite leaves are 
unequal in size, sometimes very strikingly so, a peculiarity Characteristic of 
some other genera of the family. The difference in outline in opposite leaves is 
also sometimes conspicuous. 
The size and shape of the involucral bracts are among the best characters 
by which to distinguish species in this genus, for they show little variation 
“Bull. Torr. Club 29: GS1. 1902. b3: pl. 193, 19}, 1827. 
