What You Should Know
Lactarius indigo is a species of agaric fungus in the family Russulaceae. A widely distributed species, it grows naturally in eastern North America, East Asia, and Central America; it has also been reported in southern France. Grows on the ground in both deciduous and coniferous forests, where it forms mycorrhizal associations with a broad range of trees.
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 genus Lactarius — is also indigo blue, but slowly turns green upon exposure to air. Young caps are sticky to the touch.
Lactarius indigo can be eaten plain and has a crisp body similar to the texture of an apple and can be eaten the same way. L. indigo is often eaten simply grilled, used in soups, or dried and preserved. Mushroom enthusiasts and hunters relish the experience of cooking with L. indigo, simply for how magical in appearance it is, elevating the look of any dish.
In Mexico, locals and tourists alike can see and buy these wild mushrooms for sale at the Farmers Markets. They will be sold from June through to November where they are considered as a ‘second class’ mushroom species for consumption.
Other names: Indigo Milk Cap, Blue Milk Mushroom.
Lactarius indigo Mushroom Identification
Mycorrhizal with oaks and with pines; growing alone, scattered, or gregariously; summer and fall; fairly widely distributed in North America from the northeast to the southwestern United States, Texas, and Mexico-but absent in the Pacific Northwest, on the West Coast, and in the northern Rocky Mountains.
5-15 cm; convex becoming flat or vase-shaped; the margin at first inrolled; deep to medium blue when fresh; grayish or silvery blue when faded; sometimes developing brownish areas when old; with concentric zones of color, or sometimes evenly colored; sticky or slimy when fresh; bruising and discoloring deep green, especially with age.
Attached to the stem or beginning to run down it; close; colored like the cap or a little paler; becoming nearly yellowish at maturity; staining green.
2-8 cm long; 1-2.5 cm thick; equal or tapering to base; sometimes a little off-center; slimy at first but soon dry; hard; hollowing; usually with potholes on the surface.
Whitish, turning indigo blue when cut; staining slowly greenish.
Deep indigo blue; becoming dark green on exposure.
Odor and Taste
Odor not distinctive; taste mild to (sometimes) slowly, slightly acrid.
KOH negative or yellowish on cap surface.
Spores 7-10 x 5.5-7.5 µ; broadly ellipsoid to subglobose; ornamentation about 0.5 µ high, as amyloid warts and connecting lines that sometimes form partial reticula. Pleuromacrocystidia cylindric-ventricose; inconspicuous; to about 60 x 8 µ. Cheilocystidia inconspicuous; clavate to subcylindric; to about 30 x 6 µ. Pileipellis an ixocutis. Lactiferous hyphae prominent; reddish-brown to brown in KOH.
Lactarius indigo Look-Alikes
Is found in eastern North America, which has a grayish-blue cap when young, but it has reddish-brown to purple-brown latex and gills.
Has a yellowish to dingy yellow-brown to bluish-gray cap and yellowish to brown latex.
Has blue-colored flesh in the cap and orange to red-orange flesh in the base of the stem.
Lactarius indigo Taxonomy and Etymology
Originally described in 1822 as Agaricus indigo by American mycologist Lewis David de Schweinitz, the species was later transferred to the genus Lactarius in 1838 by the Swede Elias Magnus Fries. German botanist Otto Kuntze called it Lactifluus indigo in his 1891 treatise Revisio Generum Plantarum, but the suggested name change was not adopted by others. Hesler and Smith in their 1960 study of North American species of Lactarius defined L. indigo as the type species of subsection Caerulei, a group characterized by blue latex and a sticky, blue cap.
In 1979, they revised their opinions on the organization of subdivisions in the genus Lactarius, and instead placed L. indigo in subgenus Lactarius based on the color of latex, and the subsequent color changes observed after exposure to air. As they explained:
The specific epithet indigo is derived from the Latin word meaning "indigo blue".
In central Mexico, it is known as añil, azul, hongo azul, zuin, and zuine; it is also called quexque (meaning "blue") in Veracruz and Puebla.
Photo 1 - Author: Bernard DUPONT from FRANCE (Creative Commons Attribution-Share Alike 2.0 Generic)
Photo 2 - Author: Dan Molter (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 3 - Author: Judy Gallagher (Creative Commons Attribution 2.0 Generic)
Photo 4 - Author: Alan Rockefeller (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 5 - Author: Mason Lalley (Tootybooty) (Creative Commons Attribution-Share Alike 3.0 Unported)