The leaf types are differentiated into rachis (axis of a compound leaf), pinnae (primary divisions), and pinnules (ultimate segments of a pinna).
Therefore, the final, pinnate subdivisions of each fingerlike segment may be referred to as "ultimate segments" to avoid the technical inaccuracy of calling them pinnules.
It more closely resembles A. aleuticum; however, the stalks of the ultimate segments and the false indusia are longer and the spores larger.
Under shady conditions, the ultimate segments lie within the plane of the blade, but tend to twist out of the plane when grown in the sun.
The ultimate segments of the divided blade (the apparent "pinnules") are borne on short, dark stalks of 0.6 to 1.5 mm, with the dark color often spreading into the base of each segment.
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.
Adiantum viridimontanum can be separated from the morphologically similar individuals of A. aleuticum by the greater length of the stalks on the medial ultimate segments and of the false indusia, measuring greater than 0.9 mm and greater than 3.5 mm, respectively, in A. viridimontanum.
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.
The leaves grow upto 40 cm long; they are finely dissected, with the ultimate segments filiform (threadlike), about 0.5 mm wide.
The species of this clade share short-stalked pinnae, long-aristate ultimate segments, and minutely spinulose perispore sculpturing except D. remota[ 1]. 13.
