136 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
from scattering localities in all probability affords a wholly insuffi- 
cient basis for determining the mean of the species. A suitable 
series of specimens has been available in the present study, and the 
number of species here recognized is probably not far from correct. 
As delimited below, the group of Aspleniwm trichomanes is a natural 
and fairly compact one, though there are numerous species which 
connect it with several related groups of simply pinnate species. 
Among these may be mentioned that of Asplenium viride, including 
such small species as A. fragile, A. quitense, and A. flabellifolium, 
characterized by green or greenish stipes; that of A. erectum, with a 
multitude of species, mostly with larger fronds, the stipes dull brown- 
ish to greenish or grayish green; that of A. normale, containing species 
with polished dark brown or blackish stipes and differing from the 
trichomanes group by their larger and relatively broader fronds. 
These in turn pass into bipinnate and tripinnate forms so gradually 
and in such infinite variety that a natural arrangement of the species 
of the genus as a whole is exceedingly difficult. However, keeping 
in mind the principal characters of A. trichomanes as representative, 
little difficulty need be experienced in associating the various members 
of this group, which may be characterized briefly as follows: 
ASPLENIUM TRICHOMANES GROUP. 
Small ferns, mostly 10 to 30 cm. high, the once-pinnate fronds nearly linear, tufted 
upon an erect or ascending, usually short rhizome, the stipes and rachises firm, sub- 
terete to trigonous, bright brown or castaneous to black or purplish black, minutely 
to broadly alate, sometimes sparingly fibrillose-scaly; pinnz mostly small, equilateral 
to strongly asymmetrical; venation pinnate to flabellate-dichotomous. 
The American species may be separated by means of the following 
artificial key: 
KEY TO THE SPECIES. 
Fronds mostly rooting at the tip of the flagelliform apex....... 10. A. palmeri. 
Fronds not rooting at the apex, this not flagelliform. 
Tndusia conspicuously ciliate or laciniate. 
Veins forked; indusia delicately ciliate; rachis scantily 
pubescent........ Ben aoa aan nsec ee rata es cser cess 5. A. blepharodes. 
Veins simple; indusia deeply laciniate; rachia distinctly 
fibrillose. . 2.2. eee eee ee eee ee eee 4. A. fibrillosum. 
Indusia entire to crenulate or somewhat erose. 
Fronds apparently pendent; pinnee distant................ ll. A. extensum. 
Fronds erect, ascending, or rotate; pinnz closer. 
Sterile and fertile fronds difform, the sterile ones pros- 
trate or nearly so............-..... -.+.-.-.-. 15, A, platyneuron. 
Sterile and fertile fronds similar, not arranged in two 
series, 
Sori borne mostly upon the inferior (proximal) side of 
the pinne. 
Pinne deeply cleft upon the upper margin; fronds 
very humerous, the stipes and rachises slender, 
blackish. ............ wee eee eee eee ee eeee 13. A. formosum. 
