The taxon is roughly identical to that defined for the Homobasidiomycetes (alternatively called holobasidiomycetes) by Hibbett & Thorn,[2] with the inclusion of Auriculariales and Sebacinales.

All members of the class produce basidiocarps which range in size from tiny cups a few millimeters across to a giant polypore (Phellinus ellipsoideus) greater than several meters across and weigh up to 500 kilograms (1,100 lb).

[clarification needed][11] Nearly all species are terrestrial (a few are aquatic), occurring in a wide range of environments where most function as decayers, especially of wood.

General discussions on the forms and life cycles of these fungi are developed in the article on mushrooms, in the treatments of the various orders (links in table at right), and in individual species accounts.

[15] Modern molecular phylogenetics suggest the following relationships:[16] other basidiomycetes (outgroup) Cantharellales Sebacinales Auriculariales Stereopsidales Geastrales Hysterangiales Gomphales Phallales Trechisporales Hymenochaetales Thelephorales Polyporales Corticiales Jaapiales Gloeophyllales Russulales Agaricales Boletales Amylocorticiales Lepidostromatales Atheliales There are many genera in the Agaricomycetes that have not been classified in any order or family.