The Russulaceae are a diverse

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of fungi 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 A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 Sporocarp (fungi), fruiting body of a fungus, typically produced above ground on soil or another food source. ''Toadstool'' generally refers to a poisonous mushroom. The standard for the n ...

-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 muscles, fats and other loose connective tissues, ...

of their fruitbodies. In addition to these typical

agaric An agaric () is a type of fungal 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. It is a type of mushroom (or toadstool) ...

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

secotioid Secotioid fungi produce an intermediate fruiting body form that is between the mushroom-like hymenomycetes and the closed bag-shaped gasteroid fungi, gasteromycetes, where an evolutionary process of gasteromycetation has started but not run to co ...

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 insi ...

), 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 (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

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

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 genus c ...

'', ''

Russula ''Russula'' is a very large genus composed of around 750 worldwide species of fungi. The genus was described by Christian Hendrik Persoon in 1796. The mushrooms are fairly large, and brightly colored – making them one of the most recognizable ...

'', and ''

Lactarius ''Lactarius'' is a genus of mushroom-producing, ectomycorrhizal fungi, containing several Edible mushroom, edible species. The species of the genus, common name, commonly known as milk-caps, are characterized by the milky fluid ("latex") they ex ...

''. 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 ''Boidinia furfuracea'' (formerly placed in '' Gloeocystidiellum'' ...

'', ''

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 ...

'', all wood-decay fungi, have basal positions in the family.

Taxonomy

The family Russulaceae was first validly named in 1907 by Dutch botanist Johannes Paulus Lotsy, 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 (in fungi) 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 plant ...

, 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 o ...

e and rounded cells (sphaerocytes). A prior usage of "''Russulariées''" by French mycologist Ernst Roze 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 the naming of living organisms. Standardizing the scientific names of biological organisms allows researchers to discuss findings (including the discovery of new s ...

was not used.

Synonyms A synonym is a word, morpheme, or phrase that means precisely 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 a ...

of Russulaceae include:

Ernst Albert Gäumann Ernst Albert Gäumann (6 October 1893 – 5 December 1963) was a Swiss botanist and mycologist who made contributions to plant pathology. As professor and director of the Institute for Special Botany at the Swiss Federal Institute of Technology ...

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

David Pegler David Norman Pegler (born 2 November 1938) is a British mycologist who spent his entire professional career at Kew Gardens, where he became Head of Mycology and assistant keeper of the herbarium. A leading authority on tropical agarics, he descr ...

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'', '' 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 ar ...

''. 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 Agaricales are an order of fungi in the division Basidiomycota. As originally conceived, the order contained all the agarics (gilled mushrooms), but subsequent research has shown that not all agarics are closely related and some belong in o ...

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

Agaricales The Agaricales are an order (biology), order of fungi in the division (mycology), division Basidiomycota. As originally conceived, the order contained all the agarics (gilled mushrooms), but subsequent research has shown that not all agarics are ...

, 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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

" 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 ...

. 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 ...

within the order appears to be the crust-like Gloeocystidiellaceae.

Internal systematics

A 2008 molecular phylogenetic study clarified the relationships among the mushroom-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 sc ...

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, a circumscribed circle for a set of points is a circle passing through each of them. Such a circle is said to ''circumscribe'' the points or a polygon formed from them; such a polygon is said to be ''inscribed'' in the circle. * Circum ...

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

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

, 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. 1,100 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 fungal 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. It is a type of mushroom (or toadstool), ...

'' 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. The origin of the word "cap" comes from the Old French word "chapeau" which means "head co ...

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 Basidiomycota, basidiomycete fungus, fungi, typically agarics. ...

can be found in some tropical species. Gills are adnate to

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 warm orange ("tussock") color spore print. ...

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, beech trees, with the other bei ...

''. Concentrically ringed (

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