20 
PLANTS OF YELLOWSTONE NATIONAL PARK 
Eqi'jisetum laevigatum is very similar but the tubercles are so 
minute that the stem is practically smooth. 
Equisetum robustum and E. variegatwn have also been reported as 
occurring in the park. 
QUILLWOFT FAMILY (ISOETACEAE) 
The quillworts are submerged water plants with grasslike leaves, 
but they are related to the ferns and reproduce by spores. The spore 
cases are produced on the infolded margins of the leaf bases. The 
Figure 3.—Rocky Mountain woodsia. Figure 4.—Field horsetail. Brown. 
Photograph by A. R. Sweetser. Photograph A. R. Sweetser. 
two quillworts ( Isoetes lacustris and I. bolanderi) have both been 
reported in the park. They occur in certain places in Yellowstone 
Lake. 
iCLTJBMOSS FAMILY (LYC0P0DIACEAE) 
This small family of mosslike plants is represented by one member 
in the park. The prostrate creeping stems bearing upright two- 
forked branches tipped by spores. Lycopodium annotinum has a 
solitary spike of yellowish, ovate or heart-shaped leaves concealing 
the spores which are of one kind. The spike is more or less rounded 
and oblong. The stems and branches are covered with equal, spread¬ 
ing, rigid leaves in several rows. Lycopodiums are sometimes called 
groundpine. 
