1917] Butters,— Studies in Ferns — Athyrium 203 
5. ATHYRIUM ALPESTRE AND ITS AMERICAN VARIETY. 
The typical form of Athyrium alpestre (Hoppe) Rylands ex Moore! 
is an arctic-alpine plant of Europe, ranging from Iceland to Asia 
Minor. In habit and foliage it greatly resembles A. Filix-femina, 
from which it differs in its spores, which are nigrescent and reticulate, 
and in its sori, which are smaller than those of A. Filia-femina, almost 
perfectly round, and seemingly without any indusium. Careful dis- 
section shows, however, that the receptacle of the sorus is slightly 
elongated along the vein, and under a compound microscope it is 
almost always possible to find a vestigial indusium in the same position 
that the indusium holds in forms of A. Filix-femina with round sori. . 
This indusium is about 0.3 mm. high, and may extend along the vein 
for as much as 0.25 mm., but often consists merely of two or three 
hairs joined together side by side at the base. Its cilia are always 
swollen and glandular at the tip. 
The peculiarly reduced condition of the sorus and indusium in this 
species has often lead to its being placed in genera far removed from 
the group now under consideration. Its structural general resem- 
blance to A. Filix-femina is, however, very great, and the latter species 
occasionally has semi-abortive sori with indusia almost as reduced as 
those of A. alpestre. 
A common arctic-alpine plant of North America has been tradition- 
ally identified with this species, but it differs in having the ultimate 
segments of the frond conspicuously narrower, and more widely sepa- 
rated from one another, and the sori even smaller than in the type 
(0.5-0.7 mm. in diameter as against 0.75-1.0 mm. in the typical form), 
sub-marginal and protected by a reflexed tooth of the pinnule. Care- 
1 ATHYRIUM ALPESTRE (Hoppe) Rylands ex Moore. 
Aspidium alpestre Hoppe, Neue Taschenbuch 216 (1805). 
Phegopteris alpestris Mett. Fil. Hort. Lips. 83 (1856). 
Athyrium alpestre Rylands according to Moore, Ferns of Gr. Br. and Ir. Nat. Print. 
Fol. ed. Pl. 7 (1857). 
Polypodium rhaeticum L. Sp. Pl. ii. 1091 (1753), in part. 
Polypodium Rhaeticum L. was made up of a mixture of this plant and certain forms of A. 
Filix-femina which resemble it in the form of the frond. The latter alone are represented in the 
Linnaean herbarium under this name, while to the former belongs probably the name-bringing 
synonym, Bauhin’s Filiz rhaetica ltenuissime dentata. | With sundry variations the Linnaean 
name has been employed extensively for both of these ferns. This seems to be a clear case of a 
nomen confusum, which should be rejected under the international rules. For a further dis- 
cussion of this question, see P. Ascherson, Osterreicher Bot. Zeit. 46:44. 1896. 
