Diario de erwin_pteridophilos

I want to try a short discussion about different taxonomic concepts concerning European and American population / type of Alpine lady fern, and to explain those concepts here.
There are obviousely two different kinds of Alpine lady fern in Europe and mainly western North America, and at least another one in eastern Asia which is not discussed here at time.
These two were variousely named scientifically as Athyrium alpestre, A. distentifolium and A. americanum.
We may imagine there will be some differences between two populations separated completely for considerable time, still it stays rather a question of subjective estimation and evaluation to decide about treating them as distinct species, or infraspecific varieties or subspecies.
So far not accepted as separate species, i would clearly prefer to regard European and American Alpine lady ferns as distinct subspecies isolated from each other, rather than as varieties, this rank and term might better be reserved for sympatric populations in my mind.
Different rankings as separate species or subspp. / vars. is one reason for diverging taxonomic concepts and namings.
Obviousely there is reason for some experts, to regard the oldest specific name as not valid - Aspidium alpestre Hoppe, 1805, but to prefer the later published one - Athyrium distentifolium Tausch ex Opiz, 1820.
In fact i do not know the exact reasons to reject Hoppe's older specific name, or if this interpretation is right or wrong, at least other botanists did and do accept it, treating the younger name distentifolium as synonym.
Maybe there was done a final decision in this case, i do not know of one.
Acceptance of the older name, or rejecting as invalid in favour of the later one leaded to further taxonomic combinations and confusion.
Alltogether i may consider 4 different taxonomic concepts, when including the ones to differ as varieties there are 6 different possibilities, all seem to have been applied by authors at some time.

1st concept: specific name "distentifolium" valid, "alpestre" invalid, synonymous, taxa separated as distinct species:

Europe: Athyrium distentifolium Tausch ex Opiz, 1820
North Am.: Athyrium americanum (Butters) Maxon, 1918

2nd concept: specific name "distentifolium" valid, "alpestre" invalid, synonymous, taxa separated as subspecies or varieties:

Europe: A. distentifolium subsp. / var. distentifolium Tausch ex Opiz, 1820
North Am.: A. distentifolium subsp. americanum (Butters) Hulten
North Am.: A. distentifolium var. americanum (Butters) Cronquist or (Butters) B. Boivin ?

3rd concept: specific name "alpestre" valid, "distentifolium" synonymous, taxa separated as distinct species:

Europe: A. alpestre (Hoppe) Clairv. (ex Moore ?) or (Hoppe) Nyl. ex ? Milde
North Am.: A. americanum (Butters) Maxon, 1918

4th concept: specific name "alpestre" valid, "distentifolium" synonymous, taxa separated as subspecies or varieties:

Europe: A. alpestre subsp. / var. alpestre (Hoppe) Clairv. (ex Moore ?) or (Hoppe) Nyl. ex ? Milde
North Am.: A. alpestre subsp. americanum (Butters) Lellinger
North Am.: A. alpestre var. americanum Butters, 1917

At time we got added the taxa of the first concept, Athyrium americanum and distentifolium at iNaturalist database, suggesting that Hoppe's older name was invalid.

http://www.inaturalist.org/taxa/117385-Athyrium-americanum maximal 4 at time
http://www.inaturalist.org/taxa/75694-Athyrium-distentifolium 1 (2 erron. ID) at time

In addition there is A. distentifolium var. americanum from 2nd concept, with some added observations as well.

http://www.inaturalist.org/taxa/80451-Athyrium-distentifolium-americanum 5 (6) at time

There should be done a decision between both now represented taxonomic concepts for to lead together all observations of the American population.
Any constructive contributions and comments to this are appreciated !