Latin vulcanicus, volcanic, alluding to its habitat on lava flows.
Fronds mostly erect. Blades narrow, linear, usually more than 40 cm long. Pinnae usually more than 35 pairs, close to overlapping, thick, short, coriaceous, twisted outward and upward, giving an appearance as of venetian blinds, margins shallowly crenate to wide dentate. Veins raised and prominent on abaxial surface.
Found in exposed areas, usually on open, barren lava flows and cinder, 550-2,440 m, on Moloka'i, Maui, and Hawai'i. In habitats transitional between open lava and rain forest, such as klpuka edges, intermediates between var. vulcanicum and var. pellucidum are found. When grown under greenhouse conditions, this variety develops a morphology more like that of var. pellucidum, but its lobes remain more numerous and closer together.
Polypodium pellucidum var. vulcanicum may be distinguished from var. pellucidum by its more exposed habitat; longer, narrower blades; more and thicker pinnae; and pinnae that twist outward and upward, giving a venetian-blind appearance.