Wikipedia:Today's featured article/August 8, 2013

Lactarius indigo, commonly known as the indigo milk cap, is a species of agaric fungus in the family Russulaceae. First described in 1822, it is a widely distributed species and grows naturally in eastern North America, East Asia, and Central America; it has also been reported from southern France. L. indigo grows on the ground in both deciduous and coniferous forests, where it forms mycorrhizal associations with a broad range of trees. The cap has a diameter of 5 to 15 cm. The fruit 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 blue color is due to an organic compound known as an azulene which is unique to this species, but similar to a compound found in Lactarius deliciosus. It is an edible mushroom, with a mild to slightly acrid taste; the firm flesh is best prepared by cutting the mushroom in thin slices. The blue color disappears with cooking. It is sold in rural markets in Mexico, Guatemala, and China.

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