It was originally described as Erebia pluto by Richard W. Fereday in 1872 from the Craigieburn Range in the South Island,[1] and was moved to the new genus Percnodaimon by Butler in 1876.

[4] In their 2012 guide to South Pacific butterflies, Brian and Hamish Patrick stated there are up to eight species of Percnodaimon still to be described, based on wing shape, pattern, and colour, size, behaviour, and season of emergence.

[citation needed] The wingspan of the Percnodaimon imago can be between 35 and 55 mm, and its broad velvety wings are usually black or brown across the dorsal surface, sometimes with a purple reflection.

Black mountain ringlets fly slowly in zigzag patterns, especially on a sunny day, taking advantage of thermals and often gliding in a "V" position.

"When disturbed this insect flies often with considerable rapidity and thus often eludes the net, so that the capture of a good series of specimens on a rugged mountain-slope is usually very exciting, if not actually dangerous work."

[5] The adult female black mountain ringlet deposits her eggs atop stones on alpine slopes, rather than on a larval food plant.

[8] Black mountain ringlet larvae are night feeders to avoid predators, which can easily spot them feeding on the tips of tussock blades.

Unlike most butterflies pupae are suspended horizontally rather than vertically, and are attached to the undersurface of a rock with a large cremaster, a hook-shaped protuberance on the abdomen.

Adult black mountain ringlets are found in summer, from December to February, and the Patricks note that early versus late emergence is one of the characteristics distinguishing the undescribed species.