Lactarius is a genus of mushroom-producing fungi. The genus, collectively known commonly as milk-caps, are characterized by the fact that they exude a milky fluid ('latex') if cut or damaged. Like the genus Russula, with which they are grouped in the family Russulaceae, their flesh has a distinctive brittle consistency.
Often the gills are decurrent (starting to run down the stem) and the cap is depressed or even funnel-shaped when older. The stem and cap sometimes show 'strobicules' (or 'strobiculi'), which are flat-based shallow oval pits.
To identify to which of the roughly 400 Lactarius species a given specimen belongs, note whether the cap is bald/greasy or velvety or hairy/shaggy at the rim, particularly in young individuals. Also the initial colour of the milk (white, cream, orange, violet, ...) and the final colour on drying are determining characteristics.
The genus was described by Christian Hendrik Persoon in 1797. Lactarius is derived from the Latin lac 'milk'.