136 
PLANTS OF YELLOWSTONE NATIONAL PARK 
Senecio hallii and S. mediocris have also been reported as occurring 
in the park. 
Elk thistle ( Cirsium foliosum) .—Usually 1 to 2 feet high, some¬ 
what white-woolly and leafy to the top. The leaves are narrowly 
lance-shaped, toothed, and quite prickly. The heads are nearly 2 
inches high, and the pale purple corollas are all alike. They are 
tubular, but with long, narrow lobes as long as the tubes. This 
plant has historical interest in the park since its root is edible, and 
it is said that when Truman Everts was lost in this region for more 
than a month in 1870, this plant, more than anything else, served to 
keep him from starving. 
Plains thistle ( Cirsium undulatum) is less woolly, and the stems 
and leaves are much darker 
green in color. The heads 
are only about half as 
large as those of the elk 
thistle. 
Cirsium tweedyi and 
Canada thistle (C. arvense) 
have also been reported in 
the park. 
Oysterplant ( Tragopogon 
porrifolius) .—T his is a 
smooth, perennial herb 
with alternate, grasslike 
leaves that clasp the stem 
at the base. It is com¬ 
monly 20 to 30 inches high 
and bears large heads of 
violet-purple flowers that 
are open only in the morn¬ 
ing. The corollas are all 
alike and strap-shaped and 
five-toothed at the end. 
The bracts of the involucre 
are in a single series and 
The plant is an escape from 
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w . 
fgm 
MM 
iilii 
' v> < n l- fl tk r *& 
Hi 
Figure 114.—Elk thistle. Pale purple. 
graph by Dr. Harvey E. Stork. 
Photo 
more or less united at the base, 
cultivation. 
Buckbeard ( Tragopogon pratensis) is similar but the flowers are 
yellow. 
Wirelettuce ( Stephanomeria tenuifolia) is a smooth, perennial 
herb with several slender stems 4 to 20 inches high. The leaves are 
almost grasslike, and the heads are terminal. Each head consists 
