Taxonomy and Phylogeny
German naturalist Jacob Christian Schäffer was the first to describe the species, placing it in Agaricus in 1774. Seven years later in 1781, Jean Bulliard described a species he called Agaricus necator and illustrated it in the first volume of his Herbier de la France; this name and the synonym Lactarius necator, resulting from Christian Hendrik Persoon's 1800 transfer to Lactarius, are both considered to refer to L. torminosus. Otto Kuntze, for his part chose to put it in Lactifluus, while Paul Kummer thought Galorrheus was the appropriate placement; until the recent resurrection of Lactifluus, both genera had been long considered to be unnecessary segregates of Lactarius. According to Index Fungorum, another synonym is Samuel Frederick Gray's Lactarius necans. Gray also gave the species its modern name when he transferred it to Lactarius in his 1821 Natural Arrangement of British Plants.
The specific epithet torminosus means "tormenting" or "causing colic", in reference to the gastrointestinal distress associated with consuming the raw mushroom. Early English vernacular names were Gray's "bellyach milk-stool" (1821), and James Edward Smith's "bearded pepper agaric" (1824). More recent common names include "shaggy milkcap", "powderpuff milkcap", "pink-fringed milkcap", "bearded milkcap", and the British Mycological Society-recommended "woolly milkcap".
According to Hesler and Smith's 1979 classification of the genus Lactarius, L. torminosus belongs to subgenus Piperites, section Piperites (in which it is the type species), subsection Piperites. Species in this subsection are characterized by having latex that does not turn yellow after exposure to air, and/or that does not stain the cut surface of the mushroom surface yellow. A 2004 phylogenetic analysis of European Lactarius species concluded that L. torminosus falls into a group that includes L. torminosulus, and that these two species are closely related to a group that includes L. tesquorum, L. scoticus, and L. pubescens.
A multi-gene molecular analysis published in 2008 demonstrated that species then distributed in the genera Lactarius and Russula actually consisted of four distinct lineages. The subsequent reorganization of Russulaceae species—a taxonomic change needed to make Russula and Lactarius monophyletic—required that a new type species be defined for Lactarius, since the previous type, L. piperatus, belonged to the clade that will be transferred to genus Lactifluus. A proposal to conserve Lactarius with L. torminosus as the type was accepted by the Nomenclatural Committee for Fungi and passed at the 2011 International Botanical Congress. The change minimizes "taxonomic disruption", allowing most of the common and well-known Lactarius species to retain their names.
Read more about this topic: Lactarius Torminosus