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My first impression is good. I usually leave studying the lead till I have looked at the rest of the article so that I can see whether it provides a good summary of the main text.
In the first paragraph of "Description", the subject of the second sentence is "The leaves", so you should not start the third sentence with "it".
The last sentence of paragraph 3 has the same problem, with "scales" being the subject of the first part and "it" the second.
"... at the very base of the stipe only." - I think the "only" is redundant.
"... occasionally as much as 10 centimeters (4 in)." - This presumable refers to the width but I think the sentence could be rewritten to clarify this.
"range from 6 to 35 millimeters (0.2 to 1 in) long and from 4 to 20 millimeters (0.2 to 0.8 in)" - These conversions are odd, particularly 35mm = 1 inch. I see you use {{convert|6|to|35|mm|in|sp=us|sigfig=1}} whereas I tend to use {{convert|6|to|35|mm|in|sp=us|1}}.
Where on the pinnae are the sori located?
"In addition to the A. pinnatifidum backcross with A. montanum, A. × trudellii, A. bradleyi is also capable of backcrossing with A. montanum." - I find this sentence unclear.
"It usually is under overhangs that protect it from sun and direct rain." - This sentence is awkwardly phrased.
"It has been found at altitudes from 0 to 2,000 meters (0 to 6,562 ft)." - Can you really find it being splashed by the sea?
Going back now to look at the lead, I see it mentions "sandstone" which is not mentioned in the main body of text.
The lead needs expansion; a single 11 word sentence represents the whole Description section, and a 14 word sentence the Taxonomy section.
I think I've addressed all the points here. I pulled the sentence on overhangs, which was unsourced although it does generally accord with my personal observations. Hopefully the backcrossing section is clearer now, and I've mentioned that (as per the source) sandstone is a common acidic rock. I've expanded the lead and added a bit of text to the habitat section to support that. Re. the altitudes, I suppose it depends on how much you round; one of my pictures of the species on Commons was taken at about 60 m above sea level, and I could probably push that to 30 m if I hunted around Susquehanna State Park for a day or so. (The Susquehanna River is pretty close to sea level where it cuts through the Octoraro Schist of the Piedmont, so A. montanum can actually drop pretty low on the cliffs bordering the river.) Flora of North America explicitly starts the range at "0 m", so I rephrased to drop mention of the lowest altitude. Choess (talk) 20:02, 17 December 2016 (UTC)[reply]
With regard to the altitude, that's fine. When I saw the illustration in the Distribution section I was struck by how similar the fern is to the black spleenwort here in the UK, not surprising considering your fern's taxonomical history. Cwmhiraeth (talk) 11:14, 18 December 2016 (UTC)[reply]
