the skinlike, effused, and resupinate basidioma,
often developing out of sight at the underside of
decaying wood on the ground (Larsson and
Larsson 2003 ). Examples includeAsterostroma,
Gloeocystidiellum,andBoidinia. From ancestors
with such inconspicuous basidiomata, elaborate
fruiting structures have developed, for example,
coralloid inLachnocladium,Hericium,andArto-
myces(Fig.14.8c); reflexed and bracketlike as in
Echinodontium,Stereum,Laurilia(Fig.14.8b),
and (some species of) Lentinellus;pileate-
stipitate mushrooms as inRussula,Lactarius
(Fig.14.8a), andAlbatrellus; or sequestrate as
inMacowanites(Fig.14.8d, e)andLeucophleps.
The hymenophore is most often smooth (e.g.,
Peniophora,Stereum) or hydnoid (e.g.,Auriscal-
pium,Hericium), while a poroid hymenophore
configuration is comparatively rare (e.g.,Alba-
trellus,Heterobasidion,Wrightoporia). A lamel-
late hymenophore is known from
Auriscalpiaceae (Lentinellus) and Russulaceae
only. Many species have basidiospores with an
amyloid reaction of the spore wall, and for most
of them the amyloidity is combined with an
ornamented outline of the wall.
There is no obvious morphological synapo-
morphy for Russulales, but the presence of
gloeoplerous hyphae or gloeocystidia with con-
tents rich in sesquiterpenes has not been
demonstrated in any other basidiomycete
order (Larsson and Larsson 2003 ). In a few
cases such structures seem to have been sec-
ondarily lost (e.g., in Byssoporia) or trans-
formed into homologous structures such as
the lactiferous hyphae inStereum. The term
gloeocystidiumrefers to enclosed, bladderlike
structures in fruiting bodies (Cle ́menc ̧on
2004 ). Structures termed gloeocystidia have
been reported in many orders, but the specific
type present in Russulales is associated with
unique vesicles with tubular invaginations,
which may constitute a synapomorphy for the
order (McLaughlin et al. 2008 ). In Russulales
the gloeoplerous hyphae and gloeocystidia have
been suggested to serve as a chemical defense
system against mycophagy (Sterner et al. 1985 ).
Ecological diversity: the dominant nutri-
tional strategy in Russulales is saprotophic
decay of organic matter, primarily wood. In
Russulales only white rot has been documen-
ted. It can be highly intense, for example, by
species in Stereum and Scytinostroma, and
sometimes characteristic like the white pocket
rot produced byConferticium andXylobolus
spp. (Otjen and Blanchette 1984 ). Some species
are capable of infecting living trees and perform
decay in roots or heartwood.Heterobasidion
annosumis considered the most severe forest
pathogen in conifer forests in the Northern
Hemisphere, causing economic losses of $1 bil-
lion annually in the USA alone (Woodward
et al. 1998 ). Other species with a potentially
pathogenic behavior in managed forests are
Echinodontium tinctorium, Hericium erina-
ceus,Scytinostroma galactinum, andStereum
sanguinolentum.
Another threat to forestry is caused by
wood wasps from the family Siricidae living in
symbiosis with members of Amylostereum
(Slippers et al. 2003 ). The wasp female transfers
conidia of the fungus when she places eggs
inside the wood of stressed trees using her
needlelike ovipositor organ. Larvae then feed
on the fungus while mining through fungus-
infested wood. Infection byAmylostereum are-
olatumand its vector,Sirex noctilio, normally
does not cause much damage within its native
range in Europe and Asia. However, when the
wasp was accidentally introduced into the
Southern Hemisphere and in North America,
infections in both exotic pine plantations and
native American pine stands have become
severe (Nielsen et al. 2009 ; Slippers et al. 2001 ).
ECM associationshave developed indepen-
dently within two Russulales lineages, in Rus-
sulaceae and in Albatrellaceae. Molecular
phylogenies suggest that in Russulaceae the
evolution proceeded from a saprotrophic to a
mycorrhizal nutritional strategy and coincides
with the development of erect fruiting bodies
from effused ancestors (Larsson and Larsson
2003 ). Another trend confined to the same
families is gasteromycetization (Albee-Scott
2007 ), which involves the evolution of closed
fruiting bodies adapted for a dryer climate and
animal dispersal. It is likely that change in life-
style has driven the development of erect and
closed fruiting structures since both are better
adapted for a soil-oriented life than the effused
structure typical for wood decayers.404 D.S. Hibbett et al.