'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.

Lactarius is one of the most prominent genera of mushroom-forming fungi in the Northern hemisphere. It also occurs natively in Northern Africa, tropical Africa, tropical Asia, Central America, and Australia. Its possible native distribution in South America and different parts of Australasia is unclear, as many species in those regions, poorly known, might in fact belong to Lactifluus, which has a more tropical distribution than Lactarius. Several species have also been introduced with their host trees outside their native range, e.g. in South America, Southern Africa, Australia, and New Zealand.

More Info: en.wikipedia.org