It causes Armillaria root rot in many plant species and produces mushrooms around the base of trees it has infected.

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.

[1] Numerous subtaxa have been described: 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:[6] The basidiocarp of each has a smooth cap 3 to 15 cm (1 to 6 in) in diameter,[15] convex at first but becoming flattened with age often with a central raised umbo, later becoming somewhat dish-shaped.

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.

This has a velvety margin and yellowish fluff underneath and extends outwards as a white partial veil protecting the gills when young.

Under the microscope, the spores are approximately elliptical, 7–9 by 6–7 μm, inamyloid with prominent apiculi (short, pointed projections) at the base.

[22] The symptoms are much more numerous, including slower growth, dieback of branches, yellowing foliage,[19] rotted wood at base and/or roots, external cankers, cracking bark, bleeding stem, leaf wilting, defoliation, and rapid death.

[22] In the late summer and autumn, Armillaria mellea produces mushrooms with notched gills, a ring near the cap base, and a white to golden color.

When they are attacked, the Douglas-fir, western larch and some other conifers often produce an extra large crop of cones shortly before dying.

[29] In 1893, the American mycologist Charles Horton Peck reported finding Armillaria fruiting bodies that were "aborted", in a similar way to specimens of Entoloma abortivum.

It was not until 1974 that Roy Watling showed that the aborted specimens included cells of both Armillaria mellea and Entoloma abortivum.

The whitish-grey malformed fruit bodies known as carpophoroids were the result of E. abortivum hyphae penetrating the Armillaria and disrupting its normal development.

[18] A. mellea producing rhizomorphs is parasitic on woody plants of many species, including especially shrubs, hardwood and evergreen trees.

[19] To prevent further spread, regulate irrigation to avoid water stress, keep the root collar dry, control defoliating pathogens, remove stumps, fertilize adequately, avoid physical root damage and soil compaction, and don't plant trees that are especially susceptible to the disease in places where Armillaria mellea has been recorded.

[22] Armillaria mellea mushroom are considered good edibles, though not preferred by some, and the tough stalks are usually excluded.

Some authors suggest not collecting mushrooms from the wood of various trees, including hemlock, buckeye, eucalyptus, and locust.

[35] The mushrooms have a taste that has been described as slightly sweet and nutty, with a texture ranging from chewy to crunchy, depending on the method of preparation.

Parboiling mushrooms before consuming removes the bitter taste present in some specimens, and may reduce the amount of gastrointestinal irritants.

A polyketide synthase gene, termed ArmB, was identified in the genome of the fungus, which was found expressed during melleolide production.