The Russulaceae are a diverse

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

in the order

Russulales The Russulales are an order of the Agaricomycetes, (which include the agaric genera ''Russula'' and '' Lactarius'' and their polyporoid and corticioid relatives). According to the ''Dictionary of the Fungi'' (10th edition, 2008), the order con ...

, with roughly 1,900 known

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

and a worldwide distribution. They comprise the brittlegills and the

milk-cap Milk-cap (also milk cap, milkcap, or milky) is a common name that refers to mushroom-forming fungi of the genera '' Lactarius'', ''Lactifluus'', and ''Multifurca'', all in the family Russulaceae. The common and eponymous feature of their fruit ...

s, well-known

mushroom A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans. The standard for the name "mushroom" is t ...

-forming fungi that include some edible species. These gilled mushrooms are characterised by the brittle

flesh Flesh is any aggregation of soft tissues of an organism. Various multicellular organisms have soft tissues that may be called "flesh". In mammals, including humans, ''flesh'' encompasses muscle Skeletal muscles (commonly referred to as mu ...

of their fruitbodies. In addition to these typical

agaric An agaric () is a type of fungus fruiting body characterized by the presence of a pileus (cap) that is clearly differentiated from the stipe (stalk), with lamellae (gills) on the underside of the pileus. In the UK, agarics are called "mushrooms ...

oid forms, the family contains species with fruitbodies that are laterally striped ( pleurotoid), closed (

secotioid Secotioid fungi are an intermediate growth form between mushroom-like hymenomycetes and closed bag-shaped gasteromycetes, where an evolutionary process of gasteromycetation has started but not run to completion. Secotioid fungi may or may not ...

gasteroid The gasteroid fungi are a group of fungi in the Basidiomycota. Species were formerly placed in the obsolete class Gasteromycetes Fr. (literally "stomach fungi"), or the equally obsolete order Gasteromycetales Rea, because they produce spores ins ...

), or crust-like (

corticioid The corticioid fungi are a group of fungi in the Basidiomycota typically having effused, smooth basidiocarps (fruit bodies) that are formed on the undersides of dead tree trunks or branches. They are sometimes colloquially called crust fungi or pa ...

Molecular phylogenetics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

has demonstrated close affinities between species with very different fruitbody types and has discovered new, distinct lineages. An important group of root-

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

ectomycorrhiza An ectomycorrhiza (from Greek ἐκτός ', "outside", μύκης ', "fungus", and ῥίζα ', "root"; pl. ectomycorrhizas or ectomycorrhizae, abbreviated EcM) is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobi ...

l fungi in forests and shrublands around the world includes ''

Lactifluus ''Lactifluus'' is one of three genera of mushroom-forming fungi containing species commonly named " milk-caps", the others being ''Lactarius'' and ''Multifurca''. It has been separated from ''Lactarius'' based on molecular phylogenetic evidence ...

'', ''

Multifurca ''Multifurca'' is a rare genus of ectomycorrhizal fungi in the family Russulaceae. It was described in 2008, after molecular phylogenetic study had shown that it forms a monophyletic lineage within the family, sister to '' Lactarius''. The gen ...

'', ''

Russula ''Russula'' is a very large genus composed of around 750 worldwide species of ectomycorrhizal mushrooms. They are typically common, fairly large, and brightly colored – making them one of the most recognizable genera among mycologists and mushr ...

'', and ''

Lactarius ''Lactarius'' is a genus of mushroom-producing, ectomycorrhizal fungi, containing several edible species. The species of the genus, commonly known as milk-caps, are characterized by the milky fluid ("latex") they exude when cut or damaged. Like ...

''. The crust-forming genera ''

Boidinia ''Boidinia'' is a genus of crust fungi in the family Russulaceae. The genus is widely distributed, and contains 10 species. ''Boidinia'' was described in 1982 with the type species In zoological nomenclature, a type species (''species typica'') ...

'', ''

Gloeopeniophorella ''Gloeopeniophorella'' is a genus of crust-like, wood-decaying fungi in the family Russulaceae. It contains six known species. ''Gloeopeniophorella'' was first described by Brazilian mycologist Johannes Rick Johannes (João Evangelista) Rick (1 ...

'', and ''

Pseudoxenasma ''Pseudoxenasma'' is a fungal genus in the family Russulaceae, described in 1976. The genus is monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species i ...

'', all

wood-decay fungi A wood-decay or xylophagous fungus is any species of fungus that digests moist wood, causing it to rot. Some species of wood-decay fungi attack dead wood, such as brown rot, and some, such as ''Armillaria'' (honey fungus), are parasitic and col ...

, have basal positions in the family.

Systematics and taxonomy

The family Russulaceae was first validly named in 1907 by Dutch botanist

Johannes Paulus Lotsy Johannes Paulus Lotsy or Jan Paulus Lotsy (11 April 1867 – 17 November 1931) was a Dutch botanist, specializing in evolution and heredity. He promoted the idea of evolution being driven by hybridization. Career Lotsy was born into a wealth ...

, who included three genera: ''

'', ''

'', and ''Russulina'' (now considered a synonym of ''Russula''). He emphasised features such as the granular

, thick gills, spiny

spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

, and milky

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e and rounded cells (sphaerocytes). A prior usage of "''Russulariées''" by French mycologist

Ernst Roze Ernst is both a surname and a given name, the German, Dutch, and Scandinavian form of Ernest. Notable people with the name include: Surname * Adolf Ernst (1832–1899) German botanist known by the author abbreviation "Ernst" * Anton Ernst (1975-) ...

in 1876 is not considered a valid publication, since the proper Latin termination for the family rank specified in article 18.4 of the

nomenclature code Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that species ...

was not used.

Synonyms A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

of Russulaceae include:

Ernst Albert Gäumann Ernst Albert Gäumann (6 October 1893 – 5 December 1963) was a Swiss botanist and mycologist. Born in Lyss, Canton of Bern, he obtained his early education in Biel, where he experienced both German and French languages and cultures. Studying wi ...

's Lactariaceae (1926), Fernand Moreau's Asterosporaceae (1953), and

David Pegler David Norman Pegler (born 2 November 1938) is a British mycologist. Until his retirement in 1998, he served as the Head of Mycology and assistant keeper of the herbarium at the Royal Botanic Gardens in Kew. Pegler received his BSc from London Univ ...

and Thomas Young's Elasmomycetaceae (1979). The latter family was proposed to contain species with statismosporic (non-forcibly discharged) and symmetric spores, including the gasteroid genera ''

Elasmomyces ''Russula'' is a very large genus composed of around 750 worldwide species of ectomycorrhizal mushrooms. They are typically common, fairly large, and brightly colored – making them one of the most recognizable genera among mycologists and mushr ...

'', '' Gymnomyces'', '' Martellia'', and ''

Zelleromyces ''Zelleromyces'' is a genus of fungi in the family Russulaceae. It was first described by mycologists Rolf Singer and Alexander H. Smith in 1960 to contain hypogeous (underground) fungi with gasteroid fruit bodies that "bleed" latex when they are ...

''. Calonge and Martín reduced the Elasmomycetaceae to synonymy with the Russulaceae when molecular analysis confirmed the close genetic relationship between the gasteroid and agaricoid genera.

Placement of the family

Historically, the

gilled mushrooms The fungal order Agaricales, also known as gilled mushrooms (for their distinctive gills) or euagarics, contains some of the most familiar types of mushrooms. The order has 33 extant families, 413 genera, and over 13,000 described species, along ...

of the family Russulaceae were classified with other gilled species in the order

Agaricales The fungal order Agaricales, also known as gilled mushrooms (for their distinctive gills) or euagarics, contains some of the most familiar types of mushrooms. The order has 33 extant families, 413 genera, and over 13,000 described species, alo ...

, but microscopical studies of spore and fruitbody flesh features raised the possibility that they were more closely related with certain "lower fungi" presenting nongilled, crust-like fruitbodies. The use of

molecular phylogenetics Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

confirmed that these morphologically diverse fungi form a distinct lineage, first termed the "russuloid

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

" and today classified as order

in the class

Agaricomycetes The Agaricomycetes are a class of fungi in the division Basidiomycota. The taxon is roughly identical to that defined for the Homobasidiomycetes (alternatively called holobasidiomycetes) by Hibbett & Thorn, with the inclusion of Auriculariales a ...

. The family's

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

within the order appears to be the crust-like

Gloeocystidiellaceae ''Gloeocystidiellum'' is a single genus of fungi in the monotypic Gloeocystidiellaceae family. Its species form crust-like, smooth fruitbodies. It is probably polyphyletic and may be restricted to the group around the type species In zoologica ...

Internal systematics

A 2008 molecular phylogenetic study clarified the relationships among the

-forming species of the family. The authors demonstrated the existence of four distinct lineages of gilled mushrooms, which led to the description of ''

'' as a new genus separated from ''Russula'' and the segregation of ''

'' from ''Lactarius''. Genera with closed fruitbodies within the family are

form taxa Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of s ...

instead of natural groups: ''Arcangeliella'', ''Gastrolactarius'', and ''Zelleromyces'' are phylogenetically part of ''Lactarius'', while ''Cystangium'', ''Elasmomyces'', ''Gymnomyces'', ''Macowanites'', and ''Martellia'' belong to ''Russula''. Nevertheless, some of these genus names are still in use, as many of the concerned species have not yet formally been synonymised with ''Lactarius'' or ''Russula''. The crust-like genera ''

'', ''

'', and ''

'', formerly placed in the

Corticiaceae The Corticiaceae are a family of fungi in the order Corticiales. The family formerly included almost all the corticioid (patch- or crust-forming) fungi, whether they were related or not, and as such was highly artificial. In its current sense, ...

or Gloeocystidiellaceae, are now classified in the Russulaceae and basal to the clade of mushroom-forming species described above. Studies have so far failed to clearly

circumscribe In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...

and place these genera within the family. ''Boidinia'' in its current extent is

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...

, with some species not falling into the Russulaceae.

Species diversity

Altogether, the Russulaceae comprise around 1,900 accepted species. ''Russula'' is by far the largest genus with c. 1100 species, ''Lactarius'' has c. 550, ''Lactifluus'' c. 120, ''Boidinia'' 13, ''Multifurca'' 6, ''Gloeopeniophorella'' 6, and ''Pseudoxenasma'' 1 species. Closed-fruitbody species not yet synonymised with ''Lactarius'' or ''Russula'' (''see above'') account for some 150 species. New species in the Russulaceae continue to be described from various regions, such as the US, Guyana, Brazil, Patagonia, Togo, Sri Lanka, or Thailand. It has been estimated that the real number of ''Russula'' species in North America alone (currently around 400 described) might be as high as 2000.

Cryptic species In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

may increase true diversity: some morphologically well-defined species, especially in ''Lactifluus'', have been shown to actually encompass several phylogenetic species.

Description

Macroscopic characteristics

Three major types of fruitbodies occur in the Russulaceae: ''

agaricoid An agaric () is a type of fungus fruiting body characterized by the presence of a pileus (cap) that is clearly differentiated from the stipe (stalk), with lamellae (gills) on the underside of the pileus. In the UK, agarics are called "mushrooms ...

'' and '' pleurotoid'' forms with a

cap A cap is a flat headgear, usually with a visor. Caps have crowns that fit very close to the head. They made their first appearance as early as 3200 BC. Caps typically have a visor, or no brim at all. They are popular in casual and informal se ...

gills A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

, and a stipe; forms with closed (''

'') or partially closed (''

'') fruitbodies, and ''

'', crust-like forms. The ''agaricoid'' species in ''Lactarius'', ''Lactifluus'', ''Multifurca'', and ''Russula'' are readily distinguished from other gilled mushrooms by the consistency of their flesh, which is granular, brittle and breaks easily, somewhat like a piece of chalk. Russulaceae never have a volva, but a

partial veil In mycology, a partial veil (also called an inner veil, to differentiate it from the "outer", or universal veil) is a temporary structure of tissue found on the fruiting bodies of some basidiomycete fungi, typically agarics. Its role is to isolate ...

can be found in some tropical species. Gills are

adnate Adnate may refer to: * Adnation, in botany, the fusion of two or more whorls of a flower * Adnate, in mycology, a classification of lamellae (gills) * Conjoined twins Conjoined twins – sometimes popularly referred to as Siamese twins – are ...

decurrent ''Decurrent'' (sometimes decurring) is a term used in botany and mycology to describe plant or fungal parts that extend downward. In botany, the term is most often applied to leaf blades that partly wrap or have wings around the stem or petio ...

, and the colour of the

spore print 300px, Making a spore print of the mushroom ''Volvariella volvacea'' shown in composite: (photo lower half) mushroom cap laid on white and dark paper; (photo upper half) cap removed after 24 hours showing pinkish-tan spore print. A 3.5-centimeter ...

ranges from white to ochre or orange (with the brown-spored '' Lactarius chromospermus'' as an exception). Caps can be dull to very colourful, the latter especially in ''Russula''; their size ranges from 17 mm diameter or less in '' Russula campinensis'' to in ''

Lactifluus vellereus ''Lactifluus vellereus'' (formerly ''Lactarius vellereus''), commonly known as the fleecy milk-cap, is a quite large fungus in the genus ''Lactifluus''. It is one of the two most common milk-caps found with beech trees, with the other being '' L ...

''. Concentrically ringed (

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