In 1995 we began a survey of vascular plants in the Moose River Plains and vicinity, southeast of Inlet, Hamilton Co., in the southwest Adirondacks. Our study area, with approximately the area of a 5-mile radius circle, lies mostly between 1700 and 2100 feet, although there are a few higher areas with difficult access. The study area encompasses primarily maple-birch forest, coniferous forest, sandy plains, and various acidic lakes, creeks, marshes, and boggy areas. In addition, there are very limited outcrops of calcareous marble, primarily concentrated along a single long ridge. We decided to try to define a fern circle somewhere within this study site. Early fieldwork in one small area (about 150 yards radius) with roadside access, where the calcareous ridge closely approached a marshy, acidic opening in the forest cover, revealed a concentration of 17 species. The ridge harbored Cystopteris bulbifera, C. tenuis, and Dryopteris marginalis. Although C. bulbifera is the only fern we have found in the area that is typically classified as a obligate calciphile, in our study area the other two species also appear to be restricted to calcareous substrates. In contrast, the nearby moist opening contained species such as D. cristata and D. carthusiana, which are typical of acidic environments.
This location became the nucleus of our fern circle, and we started searching for other sites with different habitats that would add species diversity. In one area where the same calcareous ridge drained into a heavily forested swamp, a circumneutral situation may have resulted from approximate cancellation of the alkaline and acidic contributions. Here we found a beautiful stand of Dryopteris goldiana, the only one known to us in the entire study site. At two similar locations along the base of the ridge, separated by 0.6 miles, we located D. clintoniana, a hexaploid species derived from the diploid D. goldiana and the tetraploid D. cristata (which itself probably was derived from the southerly diploid D. ludoviciana and another, now apparently extinct, more boreal diploid parent ). At one of these locations, perhaps two dozen D. clintoniana plants, most nearly three feet high, dominate a small drainage.
By the end of 1995, we knew of 24 fern species with a 0.5-mile radius circle centered on the calcareous ridge. We had also found Thelypteris palustris by canoe at a site that could be included within a 1-mile radius circle, bringing our total to 25 species. Furthermore, we had located two additional species, Woodsia ilvensis and Dryopteris campyloptera, at one location each within our larger vascular plant study site, suggesting that they might also occur within the circle. Woodsia ilvensis is usually found in cracks on sunny cliffs, and D. campyloptera is typical of higher elevation coniferous forests (very scarce below 2550 feet). Perusal of topographic quads suggested that the most likely location for both species was on a 2600 foot peak with a very steep south slope, bisected by a narrow "plateau", which separated the slope into two sections that might have exposed cliffs. The local forest ranger, Gary Lee, confirmed that at least the downslope cliffs had potential; at one time they had been considered as a possible hacking site for peregrine falcon, and were thought to have breeding ravens.
In our first of three hikes up this peak in 1996, we bushwhacked to the summit up the most gentle slope. Unfortunately, it was not possible to obtain satisfactory views of the upslope cliffs looking down from the summit due to dense forest cover, and the summit proved to be mostly deciduous forest, with lush Dryopteris intermedia but no evident D. campyloptera. Our second hike was to the plateau, from which we were able to view some upslope cliffs, but we could not locate Woodsia ilvensis despite careful binocular scans. However, on the return hike, on a very steep slope at the surprisingly low elevation of 2350 feet, we encountered three D. campyloptera plants, bringing the circle's total to 26 species and tying the record! This bushwhack was extremely slow because much of the hiking was on talus slopes covered with deadfall. It was very difficult to determine whether one was standing on rock or soil, or was simply suspended over a cavity in the talus by a network of branches and leaves. It was not uncommon to suddenly break through to the knees or further without notice. Despite the fact that we walked nearly continuously on this hike, with hardly any rest stops or areas requiring a speed decrease to check plants, it took us 5.5 hours to cover 1.1 miles! Our third and final hike was a last attempt to view the downslope cliffs, this time from the lower side. This shorter bushwhack, through many large glacial erratics covered by Polypodium, led to the base of roughly 125-foot high, nearly sheer cliffs. It took little time to find several cracks bearing W. ilvensis, our 27th species and the record breaker!
During the fall of 1996 we also pursued one other potential species in the circle. Recent work strongly favors separation of Polypodium virginianum into diploid P. appalachianum and tetraploid P. virginianum, the latter having arisen from P. appalachianum and P. sibiricum, an arctic species that was probably brought into contact with P. appalachianum during glacial eras, when it was forced south . Characteristics for distinguishing the diploid, tetraploid, and not infrequent triploid (hybrid) taxa are given in . The most useful difference is that of spore size, shape and color. The diploids and tetraploids have golden spores uniformly shaped like kidney beans. Triploids have abortive, translucent, irregularly shaped spores. This difference probably should be evident under a regular stereoscopic microscope. If the possibility of a triploid is eliminated by this means, chances of reliable identification are greatly increased, because the triploid is intermediate between the diploid and tetraploid in nearly all other characteristics. Mean spore size of the tetraploid is larger than that of the diploid, but there is some overlap. If external spore length (longest dimension) exceeds 59 microns, the sample is very likely tetraploid; if the length is less than 55 microns, the sample is much more likely to be diploid (some keys cite smaller numbers than these because their length measurement excludes the spore coating). We collected a series of 14 specimens from 7 areas and measured 12 spores from each using a light microscope. All but one specimen clearly proved to be diploid, and that specimen did not exhibit morphology particularly suggesting the tetraploid, so we conclude that we have only one species, P. appalachianum. Morphological differences are said to include frond tip (usually lobed in diploid, unlobed in tetraploid), blade aspect ratio (width/length > 0.40 usually diploid, < 0.30 usually tetraploid), segment tip shape (averaging more pointed in diploid), and point of greatest blade width (usually near base in diploid, near middle in tetraploid), but we have not found it easy to accurately apply these criteria.
The fern species we have found in our circle are listed alphabetically at the end of this article. Our total at the end of our field work in year 2000 is 28 species, with three additional grape ferns occurring just slightly outside the circle: Botrychium matricariifolium, B. simplex, and B. multifidum. We have also found Thelypteris simulata in our study area but the occurrence is well outside the circle. The seven Dryopteris, out of nine species in the state, seems particularly notable (the remaining two species, D. celsa and D. fragrans, are both rare in New York). The Vouchered Atlas shows ten fern species in Hamilton County that we have not found in our circle, of which Polysticum braunii might be the most likely candidate for addition to the our list. Despite the seemingly unfavorable dominant rock substrate and elevation of our study area, our fern circle effort proved to be a lot of fun and quite interesting as well, particularly with regard to the importance of microhabitats and habitat gradients in determining species diversity.
 Flora of North America Editorial Committee, Flora of North America, Vol. 2, Pteridophytes and Gymnosperms (New York: Oxford University Press), p. 281 (1993).
 C. H. Haufler and W. Zhongren, Chromosonal Analyses and the Origin of the Allopolyploid Polypodium virginianum (Polypodiaceae), Am. J. Bot., Vol. 78(5), pp. 624-629 (1991).
 L. S. Kott and D. M. Britton, A Comparitive Study of Sporophyte Morphology of the Three Cytotypes of Polypodium virginianum in Ontario, Can. J. Bot., Vol. 60, pp. 1360-1370 (1982).
Adiantum pedatum Athyrium filix-femina (A. asplenoides) Botrychium dissectum B. virginianum Deparia (Athyrium) acrostichoides Cystopteris bulbifera C. tenuis Dennstaedtia punctilobula Dryopteris campyloptera D. clintoniana D. cristata D. intermedia D. carthusiana D. goldiana D. marginalis Gymnocarpium dryopteris Matteuccia struthiopteris Onoclea sensibilis Osmunda cinnamomea O. claytonia O. regalis Phegopteris connectilis Polypodium appalachianum Polystichum acrostichoides Pteridium aquilinum Thelypteris noveboracensis T. palustris Woodsia ilvensis