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Russulaceae is a of fungi in the order Russulales. Its species have typically friable, chalk-like stalks, that break with a distinct crack, like a carrot but with porous flesh (see below). Microscopically, the cells are not all long thin hyphae, which would provide strength and more fibrous appearance when broken. Instead the flesh contains also many large spherical cells ('sphaerocysts'), which give rise to the macroscopic consistency.

Genera

The family is dominated by just two well-known genera:

• The genus Russula, sometimes known as Brittlegills, comprises around 160 species, the majority of which are quite difficult to identify. They have splitting gills and do not exude a milky substance at cut surfaces, contrarily to the genus Lactarius. There are several edible species (Russula vesca, Russula virescens or Russula aurata).

• The genus Lactarius, or Milk-caps, characterized by caps and stalks that exude a milky substance ("latex") when pressed or cut and lactiferous, gloeoplerous hyphae, is a large genus of mycorrhizal fungi. When cut, the mushroom exudes a kind of milky liquid. This liquid is may be orange, red, lilac, white or yellow, and may develop its final color only after exposure to air. Certain ones, such as L. deliciosus are edible and delicious, very much appreciated in Mediterranean areas.

However the ITIS Catalogue of life includes also the genera Cystangium, Gymnomyces, Macowanites and Zelleromyces in this family.

Distinctive Flesh Consistency

Broken stem of Lactarius vellereus

Broken stem of Suillus variegatus

Due to the presence of large spherical cells which can be seen under the microscope, an important characteristic to distinguish the Russulaceae from other types of mushrooms is the consistency of the stipe. In Russula and Lactarius, this breaks like the flesh of an apple, whilst in most other families it only breaks into fibres. The pictures compare the broken stipe of a Lactariusv ellereus, with that of Suillus variegatus, a member of the Boletaceae.

Parasites

Members of both Lactarius and Russula are subject to parasitization by the Lobster mushroom (Hypomyces lactifluorum). This ascomycete replaces the flesh of the host mushroom, rendering it into a choice edible, though it can be peppery if the host is a species like Lactarius piperatus.

These fungi may also be parasitized by the Indian Pipe, a myco-heterotrophic plant that lacks chlorophyll.