586 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
slender, the extreme condition being found in a few individuals from Sonora 
and Chihuahua in which they are very densely imbricate and exactly acicular 
from a relatively short ovate base. A similarly wide variation is noted in 
the scales of the upper surface of the segments. These, though small and 
scattered, are easily evident and usually persistent in most tropical American 
specimens; in United States plants, however, the segments are nearly or 
quite devoid of any scales above. The rhizome scales are more nearly con- 
stant, but here also there is observed a very considerable variation in size, 
form, and color, which is not altogether dependent upon age or condition. 
Another departure is found in the uniformly small plants of southern 
Brazil, Uruguay, and Argentina, which, though of rather distinct appear- 
ance, apparently do not merit recognition as a separate species, although twice 
given a name, The South African P. eckloni Kunze, also, though recognized 
by Mettenius, is very questionably distinct. 
A more or less critical examination of the very large series of specimens at 
hand, moreover, shows plainly that we have in P. polypodioides, as in 
Asplenium monanthes L., previously discussed,* a genuinely polymorphic 
species, composed of numerous elements so closely interrelated and differing 
among themselves (often regionally) in such minute and variable degree that 
segregation is scarcely justifiable. The general character of the species is too 
unmistakable and the many forms are too obviously parts of a single species 
complex, their peculiarities often clearly due to unusual conditions of habitat 
or season, 
One almost invariable characteristic of P. polypodioides, which will easily 
distinguish this species from P. thyssanolepis, its nearest ally, is found in 
the more or less immersed sori. These are always somewhat impressed, at 
least, and in a great majority of mature specimens they are so deeply set in 
pocket-like depressions of the leaf tissue that the upper side of the segment is 
strongly embossed, the location of the sori beneath being very plainly indicated 
by the double row of rounded protuberances. 
6. Polypodium thyssanolepis A. Br.; Klotzsch, Linnaea 20: 392. 1847, 
? Polypodium lanuginosum Nees, Linnaea 19: 683. 1847, not Schrad. 1824, 
nor Vell. 1827. 
Polypodium rhagadiolepis Fée, Gen. Fil. 237. 1852. 
Goniophlebium rhagadiolepis Fée, Mém. Foug. 7: 62. 1854. 
Goniophlebium thyssanolepis Moore, Ind. Fil. 396. 1862. 
Polypodium aspidiolepis Baker, Journ. Bot. Brit. & For. 25: 26. 1887. 
Polypodium purpusii Christ, Bull. Herb. Boiss. II. 7: 416. 1907. , 
TYPE LOCALITY: Colombia. 
DISTRIBUTION: Arizona; general throughout Mexico and Central America; 
less common in the Andine region of South America, but occurring from Ven- 
ezuela to Peru and Bolivia; also in Jamaica; ascends to nearly 4,000 meters. 
ILLUSTRATION : Fée, Mém. Foug. 7: pl. 19. f. 3 (as G. rhagadiolepis). 
Polypodium thyssanolepis, described originally from Colombian speciinens 
collected by Moritz (no. 22) and Otto (no. 896), is a well-known species and 
is here regarded in its usual and accepted sense. Its taxonomic history con- 
cerns principally the folowing names: 
(1) Polypodium rhagadiolepis Fée. As stated long ago by Kuhn this name, 
given to specimens collected by Linden in ‘ Cuba and Mexico,” applies to P. 
* Contr. U. S. Nat. Herb. 17: 150-152. pl. 1. 1913. 
