Lactarius

Appearance

Like many other mushrooms, ''L. indigo'' develops from a nodule, that forms within the underground mycelium, a mass of threadlike fungal cells called hyphae that make up the bulk of the organism. Under appropriate environmental conditions of temperature, humidity, and nutrient availability, the visible reproductive structures are formed. The cap of the fruit body, measuring between 5 and 15 cm in diameter, is initially convex and later develops a central depression; in age it becomes even more deeply depressed, becoming somewhat funnel-shaped as the edge of the cap lifts upward. The margin of the cap is rolled inwards when young, but unrolls and elevates as it matures. The cap surface is indigo blue when fresh, but fades to a paler grayish- or silvery-blue, sometimes with greenish splotches. It is often zonate: marked with concentric lines that form alternating pale and darker zones, and the cap may have dark blue spots, especially towards the edge. Young caps are sticky to the touch.The flesh is pallid to bluish in color, slowly turning greenish after being exposed to air; its taste is mild to slightly acrid. The flesh of the entire mushroom is brittle, and the stem, if bent sufficiently, will snap open cleanly. The latex exuded from injured tissue is indigo blue, and stains the wounded tissue greenish; like the flesh, the latex has a mild taste. ''Lactarius indigo'' is noted for not producing as much latex as other ''Lactarius'' species, and older specimens in particular may be too dried out to produce any latex.

The gills of the mushroom range from adnate to slightly decurrent , and crowded close together. Their color is an indigo blue, becoming paler with age or staining green with damage. The stem is 2–6 cm tall by 1–2.5 cm 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. Fruit bodies of ''L. indigo'' have no distinguishable odor.

''L. indigo'' var. ''diminutivus'' is a smaller variant of the mushroom, with a cap diameter between 3 and 7 cm , and a stem 1.5–4.0 cm long and 0.3–1.0 cm 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".

Naming

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" , 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

''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. It has also been collected from China, India, Guatemala, Costa Rica , 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 rainy season between June and September.

''L. indigo'' is a mycorrhizal fungus, and as such, establishes a mutualistic relationship with the roots of certain trees , in which the fungi exchange minerals and amino acids extracted from the soil for fixed carbon from the host. The subterranean hyphae of the fungus grow a sheath of tissue around the rootlets 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 enzymes that mineralize organic compounds and facilitate the transfer of nutrients to the tree.

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 Mexican white pine, Hartweg's pine, Mexican yellow pine, smooth-bark Mexican pine, and the Eurasian pines Aleppo pine, European black pine, maritime pine, and Scots pine.

Habitat

''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. It has also been collected from China, India, Guatemala, Costa Rica , 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 rainy season between June and September.

''L. indigo'' is a mycorrhizal fungus, and as such, establishes a mutualistic relationship with the roots of certain trees , in which the fungi exchange minerals and amino acids extracted from the soil for fixed carbon from the host. The subterranean hyphae of the fungus grow a sheath of tissue around the rootlets 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 enzymes that mineralize organic compounds and facilitate the transfer of nutrients to the tree.

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 Mexican white pine, Hartweg's pine, Mexican yellow pine, smooth-bark Mexican pine, and the Eurasian pines Aleppo pine, European black pine, maritime pine, and Scots pine.