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Class Agaricomycetes

The Agaricomycetes are a very large class of Basidiomycota characterized by fruiting bodies bearing hymenia consisting of a dense layer of single-celled basidia that develops on basidiospore-producing surfaces. Hymenia line the insides of pores on a conk, the surface of gills on a mushroom, the spiny projections of toothed fruiting bodies, and the exposed upper surface of simple crust-like fruiting bodies, to name a few examples. The basidia are usually club-shaped and single-celled. Other fungal genera in the class produce fruiting bodies commonly known as puffballs, coral fungi, and false truffles. 

This class consists of 23 orders, 145 families, 1,834 genera, and more than 40,500 species. Seven orders of Agaricomycetes have species within this database that are relevant to forest pathology: Agaricales, Boletales, Gloeophyllales, Hymenochaetales, Polyporales, Russulales, and Thelephorales.

Order Agaricales

The Agaricales contain most, but not all the gilled mushrooms, in 45 families, 684 genera, and more than 25,300 species. The typical agaricoid morphology is that of the capped, stalked, gilled mushroom, such as the edible Agaricus species available in the grocery store. Genomic studies have revealed that not all mushroom-forming fungi are closely related. Aside from the Agaricales, the Agaricomycetes orders Russulales and Boletales also have gilled mushroom families and genera.

Family Cyphellaceae

This family consists of species that are variable in morphology. Some are agaricoid, some lack stalks, with the cap directly attached to the substrate, and others are thin and bracket-like with a smooth non-gilled basidiospore-bearing undersurface, such as the weak pathogen and biocontrol agent Chondrostereum purpureum.

Family Physalacriaceae

This family of species consists of stalked, capped, and mostly gilled mushrooms with white basidiospores. The genus Armillaria is an important root disease pathogen of both coniferous and broadleaf trees.

Family Pleurotaceae

Commonly known as “oyster mushrooms,” this family of species consists of pale, gilled mushrooms with lateral stalks and white basidiospores. The genus Pleurotus is associated with white rot, mostly of broadleaf trees.

Family Strophariaceae

This family of species consists of mushrooms with often brightly coloured caps and yellowish to dark basidiospores with a prominent germ pore. The genus Pholiota is a weak parasite associated with wood decay. Recent studies have shown that the genus is polyphyletic with some members requiring redescription and potentially placing into different families.

Order Boletales

The Boletales are an order of mostly mushrooms, but also of other fungal fruiting body forms. This order contains most “boletoid” fungi (fleshy mushrooms with pores instead of gills under the cap, e.g., the genus Boletus). This order consists of 17 families, 80 genera, and more than 2,400 species. Most species in this order are saprotrophic or mycorrhizal.

Family Serpulaceae

This family consists of species characterized by resupinate brownish fruiting bodies with wrinkled or merulioid surfaces and brown spores. Serpula himantioides causes dry rot in wooden buildings.

Order Gloeophyllales

The Gloeophyllales consist of 1 family, the Gloeophyllaceae, with 14 genera and 56 species of fungi, many of which cause wood decay.

Family Gloeophyllaceae

This family consists of species whose fruiting bodies are tough, brownish to grayish, usually hairy and patterned with concentric zones, with the hymenium forming on pores or maze-like gills. Gloeophyllum sepiarium causes brown rot in conifer slash and wooden structures, and Veluticeps fimbriata causes brown pocket rot in conifers, both standing trees and slash.

Order Hymenochaetales

The Hymenochaetales consist of 7 families, 105 genera, and more than 1,430 species. It is likely that this order as it is currently described is in fact polyphyletic (derived from more than one common evolutionary ancestor, possibly not all related). Future genomic research on these fungi will be necessary before all members are accurately classified. This order has been traditionally characterized by brown fruiting bodies whose flesh darkens when exposed to alkali (traditionally a potassium hydroxide solution), and by the presence of setae (thick-walled, bristle-like cells) in the hymenium, but genomic studies indicate that some fungi without all these characteristics also belong in this order. For example, Trichaptum abietinum, a small polypore associated with pitted sap rot in conifers, genetically belongs in this order. Its flesh is not brown, and it does not stain dark when exposed to potassium hydroxide. Fruiting bodies that genetically belong to this order can take the form of conks, flat crusts, and other morphologies (rarely even mushroom or coral like).

Family Hymenochaetaceae

This family consists of species whose fruiting bodies are annual or perennial crust-like, mushroom-like or hoof-shaped woody conks with brown pore layers that darken when exposed to potassium hydroxide. This family contains genera causing white pocket rot in conifers (Porodaedalea, Inonotus), white rot in broadleaf trees (Phellinus), or conifer root disease (Coniferiporia).

Order Polyporales

The Polyporales consist of 26 families, 370 genera, and more than 4,000 species. This order has traditionally included most species of bracket fungi, conks, and other wood decay fungi with pores. However, recent research has shown that some species producing non-poroid fruiting bodies are also genetically related. These fruiting bodies may be corticioid (flat, crust-like with a smooth spore-bearing surface), agaricoid, or toothed. Therefore, this order is likely polyphyletic and requires further taxonomic revision.

Family Cerrenaceae

Species in this family produce fruiting bodies that range from flat to pileate with poroid, maze-like or spiny spore-bearing surfaces. Basidia are club-shaped and basidiospore walls are smooth, thin to thick, and non-reactive to iodine in Melzer’s reagent. Most species in the family are associated with a white rot decay, and a few also cause diseases of living plants, and are symbiotic with insects that act as vectors.

Family Dacryobolaceae

This family of species consists of polypores or corticioid (flat, crust-like with smooth spore-bearing surfaces) fungi that cause brown rot in conifer wood.

Family Fomitopsidaceae

This family of species consists of conks (sometimes very large and woody) or crust-like polypore fungi, associated mostly with brown rots. Most but not all species occur on conifers.

Family Laetiporaceae

This family of species consists of large fleshy annual polypores causing brown wood rot in conifers and broadleaf trees.

Family Polyporaceae

This family of species consists of poroid bracket fungi, conks, crusts, and rarely corticioid (flat, crust-like with smooth spore-bearing surfaces) fruiting bodies. Species cause a white wood rot in conifers and broadleaf trees.

Order Russulales

The Russulales are a large, morphologically diverse order of fungi containing 12 families, 110 genera, and more than 3,500 species. Species in this order are saprotrophic, parasitic, or mycorrhizal. More than two-thirds of the species in the Russulales are gilled mycorrhizal mushrooms belonging to two genera in the family Russulaceae (Russula and Lactarius). Recent genomic studies have shown that several non-gilled families are also closely related to these mushrooms despite differences in fruiting body morphology.

Those other families in the Russulales are typified by species with fruiting body morphologies that may be toothed, corticioid (flat, crust-like with smooth spore-bearing surfaces), bracket-like with pores (conks), or even coralloid. With few exceptions, all produce basidiospores that are ornamented and react with Melzer’s reagent, staining either bluish (amyloid) or reddish (dextrinoid). The flesh of species with soft fruiting bodies is made up of spherical cells, which makes them very brittle. This is especially evident in species that develop mushrooms, which shatter easily.

Family Bondarzewiaceae

This family of species consists of bracket fungi (conks) with spores produced in pores on the undersurface, including the root disease and white rot decay pathogen Heterobasidion. This genus is slightly atypical of the order because its minutely ornamented basidiospores do not colour in Melzer’s reagent.

Family Echinodontiaceae

This family of species consists of wood decay fungi on conifers and broadleaf trees (yellow stringy rot or white rot), with some producing fruiting bodies that are crust-like with smooth hymenia (Amylostereum), and others producing woody conks with toothed undersurfaces (Echinodontium).

Family Hericiaceae

This family consists of species whose soft fleshy conks have toothed undersurfaces, including the wood decay genus Hericium, associated with a white wood rot in conifers and broadleaf trees.

Family Peniophoraceae

This family consists of species that have corticioid (flat, crust-like with smooth spore-bearing surfaces) fruiting bodies, some being brightly coloured, including the parasitic wood decay genus Peniophora, associated with white wood rot in conifers and broadleaf trees.

Family Stereaceae

This family consists mostly of species with corticioid (flat, crust-like with smooth spore-bearing surfaces) fruiting bodies, including the wood decay genus Haematostereum, associated with white rot in conifer wood.

Order Thelephorales

The Thelephorales are an order of poroid, toothed, and corticioid (flat, crust-like with smooth spore-bearing surfaces) fungi, most of which are non-pathogenic and mycorrhizal. This order consists of 2 families, 21 genera, and more than 490 species.

Family Thelephoraceae

This family consists of species whose fleshy, leathery flat or fan-shaped fruiting bodies are occasionally stalked, with a smooth or bumpy hymenium, staining greenish when exposed to potassium hydroxide, due to the presence of thelephoric acid.