Percnodaimon merula, the black mountain ringlet, is a satyrid butterfly in the family Nymphalidae. It is currently the only recognised species in the monotypic genus Percnodaimon, endemic to New Zealand, although there may be other undescribed species in the genus. The black mountain ringlet is notable for living exclusively in rocky areas of New Zealand's Southern Alps, usually above 1200 m. Its eggs are laid on rocks, its larvae feed on mountain Poa species, and it pupates under a stone. It has distinctive dark velvety wings and a zig-zag flight pattern over the scree slopes on which it lives. Taxonomy This species has had a complicated taxonomic history. It was originally described as Erebia pluto by Richard W. Fereday in 1872 from the Craigieburn Range in the South Island, and was moved to the new genus Percnodaimon by Butler in 1876. It was known as Percnodaimon pluto for many years, and Wise in 1967 regarded this as the correct name for the species, but was eventually synonymised with P. merula, under which name it is usually referred to today. Most sources consider Percnodaimon monotypic, but in 2012 mitochondrial gene sequencing by Hamish Patrick for his Lincoln University Hons thesis suggested it was a species complex, with up to six species in the genus. 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. Their species list was as follows: Percnodaimon pluto (Fereday, 1872) – the commonest black mountain butterfly of the eastern South Island Percnodaimon micans (new status) – described by Augustus Hamilton in 1909 as Erebia pluto var. micans, and found in the Harris and Richardson mountains of Otago Percnodaimon sp.nov. 1 – Fiordland mountains from western Otago to Fox Glacier Percnodaimon sp.nov. 2 – Pisa Range, Otago Percnodaimon sp.nov. 3 – Eyre, Livingstone, and Takitiku Mountains to the south of Lake Wakitipu Percnodaimon sp.nov. 4 – Mountains of South Canterbury and North Otago Although the Patricks stated in 2012 that nuclear DNA was being studied with a view to formally naming and describing these species, as of 2022 that had yet to happen, and P. merula is still considered the only species in the genus. Its Māori name, pepe pouri, means "dark moth", and is applied to several ringlet species,