Zelleromyces have not yet been synonymized with Lactarius. It is estimated that a significant number of Lactarius species remain to be described. Description Macromorphology The eponymous "milk" and the brittle consistency of the flesh are the most prominent field characters of milk-cap fruitbodies. The milk or latex emerging from bruised flesh is often white or cream, but more vividly coloured in some species; it can change upon exposition or remain unchanged. Fruitbodies are small to very large, gilled, rather fleshy, without veil, often depressed or even funnel-shaped with decurrent gills. Cap surface can be glabrous, velvety or pilose, dry, sticky or viscose and is often zonate. Several species have pits (scrobicules) on the cap or pileus surface. Dull colors prevail, but some more colorful species exist, e.g. the blue Lactarius indigo or the orange species of section Deliciosi. Spore print color is white to ocher or, in some cases, pinkish. Some species have angiocarpous, i.e., closed fruitbodies. Micromorphology Microscopically, Lactarius species have elliptical, rarely globoid spores with amyloid ornamentation in the form of more or less prominent warts or spines, connected by ridges, like other members of the family Russulaceae. The trama (flesh) contains spherical cells that cause the brittle structure. Unlike Russula, Lactarius also have lactiferous, i.e. latex-carrying hyphae in their trama. Species identification Distinguishing Lactarius from Lactifluus based on morphology alone is difficult; there are no synapomorphic characters known so far that define both genera unequivocally but tendencies exist: zonate and viscose to glutinose caps are only found in Lactarius, as well as closed (angiocarpous) and sequestrate fruitbodies. All known annulate and pleurotoid (i.e., laterally stiped) milk-caps, on the contrary, belong to Lactifluus. Characters important for identification of milk-caps (Lactarius and Lactifluus) are: initial colour of the latex and color change, texture of cap surface, taste (mild, peppery, or bitter) of latex and flesh, odor, and microscopical features of the spores and the cap cuticle (pileipellis). The habitat and especially the type of host tree can also be critical. While there are some easily recognizable species, other species can be quite hard to determine without microscopical examination. Distribution 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,