An ecological study of Cheilanthes gracillima 
F..L.. .Picketr 
(WITH THIRTY-THREE TEXT FIGURES) 
Cheilanthes gracillima D. C. Eaton is found in the mountains 
of the Pacific Coast region from British Columbia to Mexico. 
It is usually found at altitudes of 5000-7000 feet, and more 
rarely as low as 1500 feet. J. H. Sandberg* reported finding 
this fern in Idaho on ‘‘mountains near Viola, Latah County, 
June 26 (1892).’’ Later surveys have located it over most of 
the range of Thatuna Hills, extending from Latah County in 
Idaho westward and northward into Whitman County, Wash- 
ington. These ‘Hills’? are old mountain peaks composed of 
granite and quartzite rocks with an altitude of 3000 to nearly 
5500 feet. They stand out in the landscape as more or less 
isolated peaks or buttes, rising 1000-2500 feet above the 
great lava plateau of the Palouse Country, as the plains of 
southeastern Washington are called. 
Throughout its range C. gracillima is an inhabitant of rocky, 
exposed ledges, and consequently has but a limited water supply. 
In the southern part of its range climatic conditions combine 
with habitat to reduce the amount of available water, so that 
this Cheilanthes has come to be known as a typical xerophytic 
species. The isolated buttes in Whitman County, Washington, 
are subject to a combination of severe conditions. The total 
rainfall of about twenty-four inches is limited almost wholly 
to the period between the first of October and the last of May. 
Throughout the summer almost constant winds with a very low 
humidity prevail. The temperature range through the year is 
from — 20° to + 110° F. Add to these conditions the fact 
that C. gracillima grows only in the crevices of otherwise bare 
rocks, with southern or southeastern exposure, with no other 
protection than an occasional dwarf specimen of Pinus ponder- 
osa, and it is at once evident that some striking characteristics 
of structure and development must be present to make possible 
the vigorous growth of this fern in this locality. The fern is 
fairly common, however, and does show normal, vigorous plants. 
* See Holzinger, Contr. U. S. Nat. Herb. 3: 267. 1895. 
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