GENERA AND SPECIES. 85 
PLATE XXIX. 
ASPIDIUM. Swartz. 
SHIELD FERN. 
GEN. CHAR.—Fruit-dots roundish, scattered on the back of the 
frond; indusium attached above the sori, round or kidney-shaped ; 
veins free, simple, or forked; stipes not articulated with the root- 
stock. 
Aspidium is one of the largest genera of ferns, and is the 
typical genus of the tribe Aspidie. Eighteen species are 
given by Mr. Redfield in his “Geographical Distribution 
of the Ferns of North America,” without including the 
six varieties enumerated by John Robinson in his excellent 
“Check List of the Ferns of North America, north of 
Mexico.” Of these seven are indigenous to Kentucky, 
so far as I have been able to discover, though it is quite 
possible that the number may be increased. 
The form of the fruit-dots and their covering (indusium) 
is the principal characteristic of this genus. The indusium 
is flat, round, or somewhat kidney-shaped, resembling a 
shield, whence the name of Shield Fern (Plate XXIX, fig- 
ure 2). This shield, in some species, is quite orbicular, 
and fixed at the center. Figure 3 shows a number of spo- 
rangia; some bursting their elastic rings. Most of the 
members of the genus are strong-growing, pinnate ferns. 
The Plate represents the Aspidium marginale, a very com- 
mon, but tall and beautiful plant. 
