page_title: Paxillus involutus
section_title: Taxonomy and naming
hierarchical_section_title: Paxillus involutus / Taxonomy and naming
caption_attribution_description: English: Original in Bulliard, JBF. (1785). Herbier de la France. Paris, France: Chez l'auteur. pp. 192–240. Plate 240. "L'Agaric contigu" (Agaricus contiguus), currently known as Paxillus involutus.
context_page_description: Paxillus involutus, commonly known as the brown roll-rim, common roll-rim, or poison pax, is a basidiomycete fungus that is widely distributed across the Northern Hemisphere. It has been inadvertently introduced to Australia, New Zealand, South Africa, and South America, probably transported in soil with European trees. Various shades of brown in colour, the fruit body grows up to 6 cm high and has a funnel-shaped cap up to 12 cm wide with a distinctive inrolled rim and decurrent gills that may be pore-like close to the stipe. Although it has gills, it is more closely related to the pored boletes than to typical gilled mushrooms. It was first described by Pierre Bulliard in 1785, and was given its current binomial name by Elias Magnus Fries in 1838. Genetic testing suggests that Paxillus involutus may be a species complex rather than a single species.
  A common mushroom of deciduous and coniferous woods and grassy areas in late summer and autumn, Paxillus involutus forms ectomycorrhizal relationships with a broad range of tree species.
context_section_description: The brown roll-rim was described by French mycologist Pierre Bulliard in 1785 as Agaricus contiguus, although the 1786 combination Agaricus involutus of August Batsch is taken as the first valid description. James Bolton published a description of what he called Agaricus adscendibus in 1788; the taxonomical authority Index Fungorum considers this to be synonymous with P. involutus. Additional synonyms include Omphalia involuta described by Samuel Frederick Gray in 1821, and Rhymovis involuta, published by Gottlob Ludwig Rabenhorst in 1844. The species gained its current binomial name in 1838 when the 'father of mycology', Swedish naturalist Elias Magnus Fries erected the genus Paxillus, and set it as the type species. The starting date of fungal taxonomy had been set as January 1, 1821, to coincide with the date of Fries' works, which meant that names coined earlier than this date required sanction by Fries (indicated in the name by a colon) to be considered valid. It was thus written Paxillus involutus (Batsch:Fr.) Fr. A 1987 revision of the International Code of Botanical Nomenclature set the starting date at May 1, 1753, the date of publication of Linnaeus' seminal work, the Species Plantarum. Hence the name no longer requires the ratification of Fries' authority.
  The genus was later placed in a new family, Paxillaceae, by French mycologist René Maire who held it to be related to both agarics and boletes. Although it has gills rather than pores, it has long been recognised as belonging to the pored mushrooms of the order Boletales rather than the traditional agarics. The generic name is derived from the Latin for 'peg' or 'plug', and the specific epithet involutus, 'inrolled', refers to the cap margin. Common names include the naked brimcap, poison paxillus, inrolled pax, poison pax, common roll-rim, brown roll-rim, and brown chanterelle. Gray called it the "involved navel-stool" in his 1821 compendium of British flora.
  Studies of the ecology and genetics of Paxillus involutus indicate that it may form a complex of multiple similar-looking species. In a field study near Uppsala, Sweden, conducted from 1981 to 1983, mycologist Nils Fries found that there were three populations of P. involutus unable to breed with each other. One was found under conifers and mixed woodlands, while the other two were found in parklands, associated with nearby birch trees. He found that the first group tended to produce single isolated fruit bodies which had a thinner stipe and cap which was less inrolled at the margins, while the fruit bodies of the other two populations tended to appear in groups, and have thicker stipes, and caps with more inrolled and sometimes undulating margins. There were only general tendencies and he was unable to detect any consistent macroscopic or microscopic features that firmly differentiate them. A molecular study comparing the DNA sequences of specimens of Paxillus involutus collected from various habitats in Bavaria found that those collected from parks and gardens showed a close relationship with the North American species P. vernalis, while those from forests were allied with P. filamentosus. The authors suggested the park populations may have been introduced from North America. A multi-gene analysis of European isolates showed that P. involutus sensu lato (in the loose sense) could be separated into four distinct, genetically isolated lineages corresponding to P. obscurosporus, P. involutus sensu stricto (in the strict sense), P. validus, and a fourth species that has not yet been identified. Changes in host range have occurred frequently and independently among strains within this species complex.
caption: Bulliard's 1785 drawing of "L'Agaric contigu" (Agaricus contiguus)
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