'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 closely related genus 'Russula', their flesh has a distinctive brittle consistency. It is a large genus with roughly 450 known species, mainly distributed in the Northern hemisphere.

Recently, the genus 'Lactifluus' has been separated from 'Lactarius' based on molecular phylogenetic evidence.

As such, they are dependent on the occurrence of possible host plants. Confirmed habitats apart from temperate forests include arctic tundra and boreal forest, mediterranean maquis, tropical African shrubland, tropical Asian rainforest, mesoamerican tropical oak forests, and Australian Eucalyptus forests.

More Info: en.wikipedia.org