Product Code Database
Lactarius indigo, commonly known as the indigo milk cap, indigo milky, indigo lactarius, blue lactarius, or blue milk mushroom, is a species of agarics in the family Russulaceae.
The basidiocarp 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. The cap has a diameter of , and the stem is tall and thick.
It is a widely distributed species, growing naturally in eastern North America, East Asia, and Central America; it has also been reported in southern France. L. indigo grows on the ground in both deciduous and coniferous forests, where it forms associations with a broad range of trees. It is an edible mushroom, and is sold in rural markets in China, Guatemala, and Mexico.
The gradual development of blue to violet pigmentation as one progresses from species to species is an interesting phenomenon deserving further study. The climax is reached in L. indigo which is blue throughout. L. chelidonium and its variety chelidonioides, L. paradoxus, and L. hemicyaneus may be considered as mileposts along the road to L. indigo.Hesler and Smith (1979), p. 7.The specific epithet indigo is derived from the Latin word meaning "indigo blue". Its names in the English common name include the "indigo milk cap", the "indigo Lactarius", the "blue milk mushroom", and the "blue Lactarius". 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.
The gills of the mushroom range from (squarely attached to the stem) to slightly (running down the length of the stem), and crowded close together. Their color is an indigo blue, becoming paler with age or staining green with damage. The stem is tall by thick, and the same diameter throughout or sometimes narrowed at base. Its color is indigo blue to silvery- or grayish blue. The interior of the stem is solid and firm initially, but develops a hollow with age. Like the cap, it is initially sticky or slimy to the touch when young, but soon dries out. Its attachment to the cap is usually in a central position, although it may also be off-center.Hesler and Smith (1979), pp. 68–9. Fruit bodies of L. indigo have no distinguishable odor.
L. indigo var. diminutivus (the "smaller indigo milk cap") is a smaller variant of the mushroom, with a cap diameter between , and a stem long and thick. It is often seen in Virginia. Hesler and Smith, who first described the variant based on specimens found in Brazoria County, Texas, described its typical habitat as "along the sides of a muddy ditch under grasses and weeds, with loblolly pine nearby".Hesler and Smith (1979), p. 70.
The blue color of L. indigo is due to (7-isopropenyl-4-methylazulen-1-yl)methyl stearate, an organic compound derivative of azulene, which is biosynthesised from a sesquiterpene very similar to matricin, the precursor for chamazulene. It is unique to this species, but similar to a compound found in L. deliciosus.
Reflecting their close relationships with trees, the fruit bodies of L. indigo are typically found growing on the ground, scattered or in groups, in both deciduous and coniferous forests. They are also commonly found in floodplain areas that have been recently submerged. In Mexico, associations have been noted with Mexican alder, American Hornbeam, American Hophornbeam, and Liquidambar macrophylla, while in Guatemala the mushroom associates with smooth-bark Mexican pine and other pine and oak species. In Costa Rica, the species forms associations with several native oaks of the genus Quercus. Under controlled laboratory conditions, L. indigo was shown to be able to form ectomycorrhizal associations with the neotropical pine species Pinus ayacahuite, Pinus hartwegii, Pinus oocarpa, smooth-bark Mexican pine, and the pines Pinus halepensis, Pinus nigra, maritime pine, and Scots pine.
In Mexico, individuals harvest the wild mushrooms for sale at farmers' markets, typically from June to November; they are considered a "second class" species for consumption. L. indigo is also sold in Guatemalan markets from May to October. In Honduras, the mushroom is called a chora, and is generally eaten with egg; generally as a side dish for a bigger meal. It is one of 13 Lactarius species sold at rural markets in Yunnan in southwestern China.
Microscopic features
When viewed in mass, as in a spore print, the basidiospore appear cream to yellow colored.Arora (1986), p. 69. Viewed with a light microscope, the spores are translucent (hyaline), elliptical to nearly spherical in shape, with amyloid warts, and have dimensions of 7–9 by 5.5–7.5 μm. Scanning electron microscopy reveals on the spore surface. The hymenium is the spore-producing tissue layer of the fruit body, and consists of that extend into the gills and terminate as end cells. Various cell types can be observed in the hymenium, and the cells have microscopic characteristics that may be used to help identify or distinguish species in cases where the macroscopic characters may be ambiguous. The spore-bearing cells, the basidia, are four-spored and measure 37–45 μm long by 8–10 μm wide at the thickest point.Hesler and Smith (1979), p. 68. Cystidia are terminal cells of hyphae in the hymenium which do not produce spores, and function in aiding spore dispersal, and maintaining favorable humidity around developing spores. The are cystidia that are found on the face of a gill; they are 40–56 by 6.4–8 μm, roughly spindle-shaped, and have a constricted apex. The —located on the edge of a gill—are abundant, and are 40.0–45.6 by 5.6–7.2 μm.
Chemical composition
A chemical analysis of Mexican specimens has shown L. indigo to contain water content at 951 mg/g of mushroom, fat at 4.3 mg/g, protein at 13.4 mg/g, and dietary fiber at 18.7 mg/g, much higher in comparison to the common button mushroom, which contains 6.6 mg/g. Compared to three other wild edible mushroom species also tested in the study ( Amanita rubescens, Boletus frostii, and Ramaria flava), L. indigo contained the highest saturated fatty acids content, including stearic acid with 32.1 mg/g—slightly over half of the total free fatty acid content.
Similar species
The characteristic blue color of the fruiting body and the latex make this species easily recognizable. Other Lactarius species with some blue color include the "silver-blue milky" ( L. paradoxus), found in eastern North America, which has a grayish-blue cap when young, but it has reddish-brown to purple-brown latex and gills. L. chelidonium has a yellowish to dingy yellow-brown to bluish-gray cap and yellowish to brown latex. L. quieticolor has blue-colored flesh in the cap and orange to red-orange flesh in the base of the stem. Although the blue discoloration of L. indigo is thought to be rare in the genus Lactarius, in 2007 five new species were reported from Peninsular Malaysia with bluing latex or flesh, including L. cyanescens, L. lazulinus, L. mirabilis, and two species still unnamed.
Distribution, habitat, and ecology
Lactarius indigo is distributed throughout southern and eastern North America but is most common along the Gulf Coast, Mexico, and Guatemala. Its frequency of appearance in the Appalachian Mountains of the United States has been described as "occasional to locally common". Mycologist David Arora notes that in the United States, the species is found with ponderosa pine in Arizona, but is absent in California's ponderosa pine forests.Arora (1986), p. 35. It has also been collected from China, India, Guatemala, Costa Rica (in forests dominated by oak), and as its southernmost distribution in the Humboldt oak cloud forests of Colombia. In Europe, it has so far only been found in southern France. A study on the seasonal appearance of fruiting bodies in the subtropical forests of Xalapa, Mexico, confirmed that maximal production coincided with the Wet season between June and September.
L. indigo is a fungus, and as such, establishes a mutualistic relationship with the roots of certain trees ("hosts"), in which the fungi exchange and amino acids extracted from the soil for Carbon fixation from the host. The subterranean hyphae of the fungus grow a sheath of tissue around the of a broad range of tree species, forming so-called ectomycorrhizae—an intimate association that is especially beneficial to the host, as the fungus produces that mineralize organic compounds and facilitate the transfer of nutrients to the tree.
Uses
Although L. indigo is a well-known edible species, opinions vary on its desirability. For example, American mycologist David Arora considers it a "superior edible", while a field guide on Kansas fungi rates it as "mediocre in quality". It may have a slightly bitter, or peppery taste, and has a coarse, grainy texture. The firm flesh is best prepared by cutting the mushroom in thin slices. The blue color disappears with cooking, and the mushroom becomes grayish. Because of the granular texture of the flesh, it does not lend itself well to drying. Specimens producing copious quantities of milk may be used to add color to .
See also
Cited literature
(1979). 9780472084401, The University of Michigan Press. ISBN 9780472084401
External links
|
|
