been used both as recreational drugs and reli-
gious sacraments (Heim and Wasson 1958 ).
Other members of Agaricomycetes are toxic,
with effects that range from gastrointestinal
distress, caused by diverse taxa such asChlor-
ophyllum molybdites, to life-threatening ama-
toxin poisoning, caused byAmanita phalloides,
Galerina autumnalis, and others (Benjamin
1995 ). The toxic compound phalloidin (from
A. phalloides) binds to actin, making it useful
as a component of fluorescent stains for visua-
lizing the cytoskeleton.
Agaricomycetes are not common as human
pathogens, althoughSchizophyllum commune,
which normally occurs as a wood-decay fungus,
is known to cause serious infections of lungs
and other organs (Sigler et al. 1995 ). Several
Agaricomycetes have been important as model
systems in studies of fungal mating genetics
and development (S. commune, Coprinopsis
cinerea) (Ohm et al. 2010 ; Raper and Miles
1958 ; Stajich et al. 2010 ) and the biochemistry
of wood decay (Phanerochaete chrysosporium,
Postia placenta, and others) (Martinez et al.
2004 , 2009 ). Finally, there is interest in uses of
Agaricomycetes in industrial bioconversion
processes and bioremediation (Ruiz-Duen ̃as
and Martı ́nez 2009 ).
Most of the taxa now classified in the Agar-
icomycetes were included in a chapter on
Homobasidiomycetes in the previous edition
of The Mycota (Hibbett and Thorn 2001 ).
Eight informally named clades (e.g., euagarics
clade, russuloid clade) were proposed, based
almost entirely on analyses of ribosomal RNA
(rRNA) gene sequences. A separate chapter
treated Heterobasidiomycetes (Wells and Ban-
doni 2001 ), which included jelly fungi and
others with mostly septate basidia (Weiß et al.
2004a). Today, Agaricomycetes is recognized as
one of four major clades of Agaricomycotina,
the others being the Dacrymycetes (see Ober-
winkler 2014 ), Tremellomycetes (see Weiß et al.
2014 ), and Wallemiomycetes (Fig. 14.1)
(Hibbett 2006 ; Padamsee et al. 2012 ). The 2007
AFTOL classification of Fungi (Hibbett et al.
2007 ) included 17 orders of Agaricomycetes,
three of which contain species formerly classi-
fied as Heterobasidiomycetes, namely Auricu-
lariales, Sebacinales, and Cantharellales pro
parte (i.e., Ceratobasidiaceae and Tulasnella-
ceae). Since 2007, three new orders of Agarico-
mycetes have been proposed: Amylocorticiales,
Jaapiales, and Lepidostromatales (Binder et al.
2010 ; Hodkinson et al. 2013 ). This chapter pro-
vides a phylogenetic overview of Agaricomy-
cetes, emphasizing recent molecular studies
that address the diversity and phylogenetic
relationships of each order (of course, clades
of Agaricomycetes classified as orders are sim-
ply mutually exclusive groups; they are not
necessarily equivalent in age, number of spe-
cies, or phenotypic diversity).A. Higher-Level RelationshipsAll currently recognized orders of Agaricomy-
cetes have been resolved as monophyletic in
at least one analysis of rRNA genes, but sup-
port for some groups has been weak or
absent, in part because of elevated rates of
evolution in nuclear rRNA (nrRNA) genes in
certain Cantharellales and other lineages
(Binder and Hibbett 2002 ; Binder et al. 2005 ;
Hibbett et al.1997b; Moncalvo et al. 2006 ).
Genes encoding proteins, such as subunits 1
and 2 of RNA polymerase II (rpb1, rpb2),
mitochondrial ATPase subunit 6 (atp6), and
translation elongation factor 1-a (tef1),
started to be used in fungal molecular system-
atics in the late twentieth century (Kretzer
and Bruns 1999 ; Liu et al. 1999 ; O’Donnell
et al. 2001 ), and by 2006 a 6-gene, 200-
species, kingdom-wide fungal phylogeny had
been produced that included 37 species of
Agaricomycetes (James et al. 2006 ). The first
in-depth study of Agaricomycetes combining
rRNA and protein-coding genes was that of
Matheny et al. ( 2007 ), who analyzed a 6.6 kb
data set ofrbp2,tef1, and nrRNA genes in 146
species (119 species of Agaricomycetes). This
was the first analysis to provide strong sup-
port for the monophyly of Polyporales (which
had been weakly supported in rRNA ana-
lyses), and it suggested that the Sebacinales,
Cantharellales, Auriculariales, and Phallomy-
cetidae formed a paraphyletic assemblage,
within which a clade containing the remain-
ing Agaricomycetes is nested.374 D.S. Hibbett et al.