The species were initially considered part of Stereum until mycologist Jacques Boidin found atypical microscopic differences between them.

Three Amylostereum species are symbionts of wood wasps in the genera Sirex, Urocerus, and Xoanon, which infest conifers.

The fungus propagates vegetatively through the formation of asexual spores in newly emerged females that are stored in special structures adapted for the transport of symbiotic fungi.

The A. areolatum–Sirex noctilio symbiont complex has been studied extensively because of its potential to cause substantial economic losses in the forestry industry, particularly in non-native regions.

Amylostereaceae species were for a long time classified in the genus Stereum, based primary on the layered structure of the fruit body and the similar physiological activity.

Mycologist Jacques Boidin separated Amylosterum from Stereum in 1958, justifying this decision by explaining that microscopic differences such as amyloid spores and encrusted cystidia were sufficiently distinct to warrant recognition as a new genus.

[2] Based on DNA analysis, Boidin in 1998 moved Amylostereum into a new, monotypic family, the Amylostereaceae, which he attributed to the Hericiales order.

[7] Experiments with pure cultures of the fungi, however, showed that the mycelia of A. chailletii, A. laevigatum and A. ferreum were partially compatible to each other, but the mycelium of A. areolatum was incompatible to other species.

[6] As A. areolatum and A. chailletii mainly reproduce asexually through the symbiosis of wood wasps, the genetic variability within these species is relatively low.

The fruit bodies are 0.5–1.5 mm (0.02–0.06 in) thick, irregularly shaped and are able to cover a large surface on the bark or otherwise can appear as small spots.

The ochrous, grey or brownish fruit body (hymenium) has a smooth to warty surface texture and is turned outwards.

[7] It is bordered by a highly bent and wavy (effuso-reflex) edge on all species except A. laevigatum, which has a churlish surface (a tomentum) and is usually dirty-brown coloured.

These hyphae run parallel to the bark and often have hairpin-like turns, so that the loops form thick-walled, cystidium-like structures, the so-called pseudocystidia.

Although they are colourless and hyaline, the spores are amyloid, meaning they will turn bluish or purple when stained with Melzer's reagent.

Symbioses have been recorded with several species: Sirex noctilio, S. juvencus, S. nitobei, S. cyaneus, S. edwarsii, S. nitidus,[10][11] and, in Japan, Urocerus antennatus[12] and Xoanon matsumurae.

[13] Wasps of the genera Sirex and Urocerus store oidia (the hypha of fungi split up to spores) in special abdominal organs.

The wood wasps infect trees by splashing a phytotoxic secretion below the bark and at the same time injecting fungal spores into the hole.

The host spectrum of A. laevigatum comprises Cupressaceae such as junipers (Juniperus) or cypresses (Cupressus) and the English yew (Taxus baccata).

Symptoms of infestion by the symbiotic partner—wood wasps—include circular exit holes in the crust and acute stress through dryness, common in hanging, falling or tanning needles.

The wasp's phytotoxic secretion, its larvae and the fungus combine very effectively with each other and contribute to forest decline rates of up to 80%.