Environmental studiesare expanding our
concepts of the ecological roles and diversity of
Agaricomycetes (Hibbett et al. 2011 ). ECM and
soil communities have been studied intensively
for many years (Horton and Bruns 2001 ; Peay
et al. 2008 ), but molecular environmental
surveys are demonstrating the occurrence of
diverse Agaricomycetes in other, often
surprising, habitats. For example, a small num-
ber of freshwater, marine, and mangrove-
inhabiting Agaricomycetes are known from
cultures and fruiting bodies (Binder et al.
2006 ; Hibbett and Binder 2001 ; Frank et al.
2010 ; Jones and Fell 2012 ; Yamaguchi et al.
2008 ), but recent studies using molecular
approaches have detected Agaricomycetes in
marine planktonic communities (Gao et al.
2010 ) and in corals, which seem to harbor spe-
cies of Agaricales, Auriculariales, Boletales,
Corticiales, Hymenochaetales, Polyporales,
and Russulales (Amend et al. 2012 ). The func-
tional biology of these marine taxa, known only
from DNA sequences, remains obscure.
Numerous species of Agaricomycetes have
also been discovered as endophytes (Oses
et al. 2008 ; Rungjindamai et al. 2008 ; Thomas
et al. 2008 ; Weiß et al. 2011 ). For example,
culture-based studies of the foliar and sapwood
endophytes of the rubber treeHevea brasilien-
sishave detected many species of Polyporales
(almost all white rot taxa), as well as Agaricales,
Atheliales, Auriculariales, Cantharellales,
Hymenochaetales, and Russulales (R. Gazis
and R. Martin, unpublished). Most of the sap-
wood endophytes are closely related to known
wood-decay species, suggesting that the endo-
phytes may exist as latent saprotrophs. Other
ecological associations of Agaricomycetes that
have received significant attention recently
include lichenized and lichenicolous forms
(DePriest et al. 2005 ; Diederich et al. 2011 ;
Diederich and Lawrey 2007 ;Lawreyetal. 2007 )
and insect symbionts (Aanen et al. 2002 ; Mueller
et al. 2005 ;Nobreetal. 2011 ; Slippers et al. 2003 ).
The latter group includes Fibulorhizoctonia
(Atheliales), which produces sclerotia that
mimic the eggs of its termite symbionts
(Matsuura 2006 ;Matsuuraetal. 2009 ).
C. Fossils and Molecular Clock DatingMolecular clockstudies have yielded diverse
age estimates for Fungi, with the origin of the
Basidiomycota inferred to be anywhere from
450 million years ago (mya) to over 1 billion
years ago (Berbee and Taylor 2010 ; Blair 2009 ;
Douzery et al. 2004 ; Gueidan et al. 2011 ; Hedges
et al. 2004 ; Taylor and Berbee 2006 ). A genome-
based molecular clock analysis (Floudas et al.
2012 ) estimated the age of the Agaricomycetes
at ca. 290 million years (with a 95 % highest
posterior density interval of 222–372 million
years). Other molecular clock studies using
rRNA genes, alone or in combination with
selected protein-coding genes, have focused
on groups within Agaricomycetes, such as Bole-
tales (Skrede et al. 2011 ; Wilson et al. 2012 ),
Agaricales (Matheny et al. 2009 ; Ryberg and
Matheny 2012 ), and brown-rot lineages
(Garcia-Sandoval et al. 2011 ). Taxon sampling
in these analyses has been very divergent, and
their results have often been inconsistent. For
example, an analysis focused on Inocybaceae
(Agaricales) (Matheny et al. 2009 ) suggested
that the group arose 143 (99–191) mya, while
another study that focused on Boletales but
included diverse Agaricales (Skrede et al.
2011 ) suggested that the common ancestor of
Inocybaceae and Crepidotaceae existed ca. 45
(30–60) mya.
New genome sequences are providing a
wealth of data for molecular clock analyses in
Agaricomycetes, but the paucity of reliably
identifiedfossilscontinues to be a limiting fac-
tor. Basidiomycetous hyphae with clamp con-
nections are known from the Pennsylvanian
(ca. 330 mya) (Dennis 1970 , 1976 ; Krings et al.
2011 ; see Taylor et al., Chap. 10, Vol. VII, Part
B), but the earliest fossils that are clearly Agar-
icomycetes do not occur until the Cretaceous.
The oldest, Quatsinoporites cranhamii,isa
fragment of a poroid hymenophore from the
lower Cretaceous (130–125 mya) that has sim-
ple (nonclamped) septate hyphae and hymenial
elements that resemble setae, suggesting that it
may be a member of Hymenochaetales (Smith
et al. 2004 ). Two gilled mushrooms that are386 D.S. Hibbett et al.