Lactarius indigo, commonly known as the indigo milk cap, the indigo Lactarius or the blue Lactarius, is a species of fungus in the Russulaceae family of mushrooms. A widely distributed species, it grows naturally in eastern North America, East Asia, and Central America. L. indigo grows on the ground in both deciduous and coniferous forests, where it forms mycorrhizal associations with a broad range of trees. The fruiting body color ranges from dark blue in fresh specimens to pale blue-gray in older ones. The milk, or latex, that oozes when the mushroom tissue is cut or broken a feature common to all members of the Lactarius genus is also indigo blue, but slowly turns green upon exposure to air. The cap is typically between 5 to 15 cm (2 to 6 in) broad, and the stem 2 to 8 cm (0.8 to 3.1 in) tall by 1 to 2.5 cm (0.4 to 1.0 in) thick. It is an edible mushroom, and is sold in rural markets in Mexico, Guatemala, and China.