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.
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.
Photographs of fresh unpressed pinnae supplemented by macrophotographs of the abaxial surface of individual ultimate segments were used for the examination of gross features of laminal dissection, presence/absence of free laminal lobes on pinna and pinnule axes, and abaxial laminal indumentum.
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.
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.
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.
It more closely resembles A. aleuticum; however, the stalks of the ultimate segments and the false indusia are longer and the spores larger.
Ortega (1990) found in Venezuela both typical P. e. arachnoideum and a second more compact form lacking free lobes between ultimate segments, while Schwartsburd et al. (2014) recognized three morphotypes of P. e. arachnoideum from Brazil.
The species of this clade share short-stalked pinnae, long-aristate ultimate segments, and minutely spinulose perispore sculpturing except D. remota[ 1]. 13.
