Armillaria mellea

Armillaria mellea, commonly known as honey fungus, is an edible basidiomycete fungus in the genus Armillaria. It is a plant pathogen and part of a cryptic species complex of closely related and morphologically similar species. It causes Armillaria root rot in many plant species and produces mushrooms around the base of trees it has infected. The symptoms of infection appear in the crowns of infected trees as discoloured foliage, reduced growth, dieback of the branches and death. The mycelium is capable of producing light via bioluminescence.

The mushroom is widely distributed in temperate regions of the Northern Hemisphere. It typically grows on hardwoods but may be found around and on other living and dead wood or in open areas.

The species was originally named Agaricus melleus by Danish-Norwegian botanist Martin Vahl in 1790; it was transferred to the genus Armillaria in 1871 by Paul Kummer. Numerous subtaxa have been described:

MycoBank also lists f. mellea, subsp. mellea, and var. mellea as current with a "(?)".

Armillaria mellea once included a range of species with similar features that have since been reclassified. The following are reassigned subtaxa, mostly variety-level entries from the 19th century:

It is commonly known as honey fungus, stump mushroom, stumpie, honey mushroom, pipinky or pinky,^{[citation needed]}

The basidiocarp of each has a smooth cap 3 to 15 cm (1 to 6 in) in diameter, convex at first but becoming flattened with age often with a central raised umbo, later becoming somewhat dish-shaped. The margins of the cap are often arched at maturity and the surface is sticky when wet. Though typically honey-coloured, this fungus is rather variable in appearance and sometimes has a few dark, hairy scales near the centre somewhat radially arranged. The gills are white at first, sometimes becoming pinkish-yellow or discoloured with age, broad and fairly distant, attached to the stipe at right angles or are slightly decurrent. The flesh of the cap is whitish and has a sweetish odour and flavour with a tinge of bitterness.

The stipe is of variable length, up to about 20 cm (8 in) long and 3.5 cm (1+1⁄2 in) in diameter. It is fibrillose and of a firm spongy consistency at first but later becomes hollow. It is cylindrical and tapers to a point at its base where it is fused to the stipes of other mushrooms in the clump. It is whitish at the upper end and brownish-yellow below, often with a very dark-coloured base. There is a broad persistent skin-like ring attached to the upper part of the stipe. This has a velvety margin and yellowish fluff underneath and extends outwards as a white partial veil protecting the gills when young.