The leaf blade is cut into finger-like segments, themselves once-divided, which are borne on the outer side of a curved, dark, glossy rachis.

Spores are borne under false indusia at the edge of the subdivisions of the leaf, a characteristic unique to the genus Adiantum.

It can generally be separated from A. pedatum by the shape of the ultimate segments (the smallest divisions of the leaf), and by its habitat on thin, exposed serpentine soils rather than in rich woodlands.

It more closely resembles A. aleuticum; but the stalks of the ultimate segments and the false indusia are longer and the spores larger.

It thrives on sunny, disturbed areas where ultramafic rock is covered with thin soil, such as road cuts, talus slopes, and asbestos mines.

It is one of four species endemic to serpentine in eastern North America and is considered globally threatened due to its habitat restrictions.

Therefore, even though they appear structurally similar, the longest and most central fingerlike segment represents the tip of the frond, pinnately divided into pinnae (the first level of division of the frond), while the two shorter fingerlike segments immediately on either side of it are pinnae, pinnately divided into pinnules (the second level of division).

Their tissue is herbaceous (firmly leafy) to chartaceous (parchment-like) in texture, and bright green to bluish-green in color.

[2] The sporangia (the fern's spore-bearing structures) are borne on the underside of the leaf beneath the false indusium, a trait found in all members of Adiantum and not in any species outside it.

[2][8] One potentially distinguishing character is the shape of the ultimate segments in the middle part of the leaf blade, which are oblong in A. pedatum and long-triangular or reniform (kidney-shaped) in A. viridimontanum and some specimens of A. aleuticum.

In A. aleuticum growing as a disjunct on eastern serpentine (the specimens most likely to be confused with A. viridimontanum), the rhizome is much more frequently branched, with intervals of 1.0 to 2.0 mm between nodes.

[2] The work which led to the recognition of Adiantum viridimontanum as a distinct taxon began in the early 20th century.

aleuticum, on the serpentine tableland of Mount Albert by Merritt Lyndon Fernald in 1905,[9] botanists began to search for western maidenhair on ultramafic outcrops elsewhere in Quebec and Vermont.

[13] In 1988, Paris and Michael D. Windham published the results of this analysis, revealing A. pedatum in North America to be a cryptic species complex.

This allotetraploid was also morphologically intermediate between the two taxa, although it more closely resembled the serpentine taxon (hence its referral to var.

The type specimen of A. viridimontanum was collected from a talus slope at the old asbestos mine on Belvidere Mountain on August 28, 1985.

At least seven stations in Vermont lie in the Missisquoi Valley, in the northern Green Mountains, giving the fern its common name.

[17][18] The fern thrives in thin serpentine soils on sunny, disturbed habitats such as roadcuts and talus slopes, in dunite and other ultramafic rocks.

Anthropogenic disturbance has removed thicker soils and increased sun exposure in many of these sites; for instance, many of the Quebec stations are in asbestos mines, both abandoned and active.

These requirements allow A. viridimontanum to colonize recently disturbed sites on ultramafic outcrops, where bedrock has been exposed and competing plants have been removed.

In general, ferns are less susceptible to herbivory than flowering plants due to higher levels of toxic and distasteful compounds in their foliage.

[1] Conservation of A. viridimontanum is primarily limited by its restricted habitat on serpentine cliffs and talus slopes which are of little value to humans.