A grey crustose lichen formerly collected in the Auvergne region of France for use in making a violet dye.
The lichen was identified by 18th-century botanists with the crab's-eye lichen, Ochrolechia parella, though the term seems to have referred also to other species such as Pertusaria dealbescens..
Origin
Early 18th century; earliest use found in John Browne (1642–?1702/3), surgeon. From French perelle from Occitan peirèla name of a lichen, probably from peira stone + -ela. In forms parelle, parella after the French variant parelle, which may have arisen by confusion with French parelle red dock, and is probably also the source of scientific Latin parellus (in Lichen parellus, Linnaeus Mantissa Plantarum 132). Compare.