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40
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Decay fungi of riparian trees in the
Southwestern U.S.
Jessie A. Glaeser and Kevin T. Smith
…the hazard tree specialist needs
a working knowledge of the fungi
associated with hardwood decay.
Introduction: Most of the tree species
that characterize riparian woodlands
are early or facultative seral species
including Fremont cottonwood (Popu-
lus fremontii), Arizona alder (Alnus
oblongifolia), Arizona sycamore (Plata-
nus wrightii), Modesto ash (Fraxinus
velutina), boxelder (Acer negundo), and
narrowleaf poplar (Populus angustifo-
lia). Arizona walnut (Juglans major) is
a riparian species that can persist at
a low density in late seral or climax
forests.
The Southwest is a harsh environ-
ment for trees. The frequent occur-
rence of early-seral tree species in
riparian forests reflect the frequency,
severity, and extent of disturbance
events. Disturbance from fire, sea-
sonal flooding, and landslides all
provide special opportunity for
injury and infection by wood decay
fungi. Even riparian species can un-
dergo periodic drought conditions
as water levels drop during the heat
of summer. Human activity can lead
to soil compaction and root damage.
Stressed trees are more susceptible
to agents of mortality, including “op-
portunistic pathogens” that are only
able to cause disease in weakened
trees. Infections in a young tree can
produce a cascade of processes that
result in long-standing decay and
cavities in large, mature individuals.
As the tree loses structural support to
decay, it becomes a potential hazard.
The degree of hazard depends on the
physical condition of the tree, includ-
ing the presence of cracks and weak
branch attachments, as well as the size
and position of decayed wood and
cavities. Identification of the fungi
responsible for the decay improves
prediction of tree performance and
the quality of management decisions,
including tree pruning or removal.
Consequently, the hazard tree spe-
cialist needs a working knowledge of
the fungi associated with hardwood
decay. We present here some of the
common fungi responsible for decay
of riparian species of the Southwest.
Many of these fungi are nonspecial-
ized and will be encountered fre-
quently throughout North America.
Wood decay fungi can be grouped
in different ways. Academic my-
cologists use evolutionary or genetic
relationships, largely discerned from
DNA sequence analyses, to group
fungi. In recent years, improved
analytical techniques have greatly in-
creased our understanding of fungal
evolution and upended many tradi-
tional groupings of fungi that shared
morphological similarities. Ecological
groupings based on observations
of fungal habitat, spatial position,
and the appearance of the decayed
wood (Tainter and Baker 1996), are
also relevant to the hazard tree spe-
cialist. White-rot fungi degrade the
lignin, cellulose and hemicellulose
of wood, leaving behind a white or
off-white residue. Some white-rot
fungi produce many small pockets
of decay throughout the infected
volume of wood, a condition known
as “pocket rot”. Brown-rot fungi, on
the other hand, degrade the cellulose
and hemicellulose in the wood cell
wall, but do not significantly degrade
the lignin. Brown-rotted wood in ad-
vanced decay is often seen as more
or less cubical fragments. Eventu-
ally, brown-rotted wood becomes
a brown residue, composed largely
of lignin, which becomes part of soil
humus and resists further degrada-
tion. This brown-rot residue is an
important component of the carbon
sequestered in forest soil. White-rot
fungi frequently decay hardwoods,
and brown-rot fungi often colonize
conifers, but many exceptions occur.
The decayed wood within the tree
can take different forms described by
its appearance and texture, including
“stringy rot,” “spongy rot,” “pocket
rot,” “cubical rot,” and “laminated
rot.” Each of these decay types has
different physical properties that af-
fect the amount of strength remaining
in the wood. In brown-rot decay, large
amounts of strength loss occur early
in the decay process due to the rapid
depolymerization of cellulose (Cowl-
ing 1961). In white rot, wood strength
declines more gradually with time.
An eco-nutritional approach
groups some wood decay fungi as
saprotrophs that attack wood in ser-
vice or as felled logs, slash, or snags
(Toupin et al. 2008) or as pathogens
that decay wood in living trees.
Pathogenic wood decay fungi can be
further subdivided based on the type
of wood degraded and the position
of the fungus within the living tree.
Heartrot fungi can decay heartwood
in living trees despite the tree’s abil-
ity to produce protective chemicals
and low oxygen conditions in the
central cylinder (Highley and Kirk
1979). When sapwood is exposed by
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mechanical injury, many saprot fungi
can act as primary pathogens and
directly kill living cells in advance of
infection. These include canker rot
and many root rot fungi (Shortle et al.
1996). Fruiting bodies of saprot fungi
around the outer circumference of the
stem can indicate structural weak-
ness and increased risk for climbing
arborists.
Many decay fungi can be catego-
rized using the above static criteria.
However, the great advance in un-
derstanding of the biology of wood
decay in living trees involves the
compartmentalization process (Shigo
1984), a foundation concept in forest
pathology (Manion 2003). Prior to the
description of the compartmentaliza-
tion process, heartrot was thought to
form by the direct infection of dead
heartwood exposed by injury. In the
compartmentalization concept, heart-
rot generally begins with the infection
of sapwoodd by a succession of fungi.
The spread of those fungi throughout
the tree is resisted through the bound-
aries and barriers of compartmental-
ization (Smith 2006). As the vascular
cambium continues to produce new
xylem to the outside of existing wood,
and healthy sapwood continues to be
converted into heartwood, the infec-
tion becomes more or less centered in
the middle of the tree. The early-seral
tree species in this group do not have
a strong compartmentalization re-
sponse to resist the spread of infection
after the wounding of live sapwood.
Dead wood, including the dead wood
attached to living trees, is generally of
low durability and therefore decays
readily. The inability of these species
to compartmentalize and limit the
development of further decay makes
them particularly hazardous in highly
trafficked areas.
The types of decay, morphologi-
cal features of the fruiting body, and
a short discussion about the impact
on hazard tree analysis are presented
for some of the major decay fungi
associated with riparian trees in the
Southwest. A glossary of mycological
terms is included.
Armillaria mellea
Although the traditional concept
of A. mellea has been split into 10
biological species in North America,
the name is still valid for the root-rot
fungus present on hardwoods and
some conifers in California and the
Southwest. Fruiting bodies are gilled
mushrooms, produced in clusters
usually of 8 – 10 but sometimes 30 or
more. The cap (pileus) is honey-col-
ored, 3-13 cm wide, generally with a
smooth surface, but which may show
a few sparse hairs or scales on the up-
per surface. Gills are attached to the
stalk (stipe), which tapers at the base
and usually has a persistent ring, or
“annulus,” at the upper portion. Black
rhizomorphs form on the surface of
colonized roots and under the bark
of infected trees (Burdsall and Volk
1993). Mycelial fans may also form
Glossary: Definitions of mycological terms
(Gilberston and Ryvarden, 1987)
Annulus – a ring found on the stipe of certain mushrooms.
Applanate– thin, flattened horizontally. Usually used to describe ses-
sile fruiting bodies or the pileate portion of effused-reflexed fruiting
bodies.
Dimidiate – semi-circular in outline when viewed from above.
Effused – flat (resupinate) with no pileus or shelf. Adheres entirely
to the substrate.
Effused –reflexed – a fruiting body that is partially resupinate and
partially shelving into the pileus.
Mycelium – the vegetative stage of the fungus, usually observable as
a mass of individual threads, termed “hyphae.”
Ochraceous – a yellowish buff color.
Pileus – the portion of a fruiting body with a sterile upper surface
and a fertile lower surface.
Resupinate – flat
Rhizomorph – a macroscopic strand, often resistant to drying, that
spreads throughout the soil. Black in Armillaria species.
Sessile – without a stipe [or stalk]
Stipe – stalk-like or stem-like structure that supports the pileus.
Stipitate – with a stipe. The stipe can be central or attached later-
ally (eccentric).
Ungulate – hoof-shaped.
Armillaria mellea cluster Armillaria mellea gills
42
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beneath the bark of diseased roots and
the root crown. Armillaria mellea may
be the most virulent species of Armil-
laria in California, causing a serious
whiterot of roots, especially in over-
watered urban trees (Baumgartner
and Rizzo 2001 a & b). Infected wood
initially appears water-soaked, then
becomes light colored and spongy
with more advanced decay (Swiecki
and Bernhardt 2006). It is also found
among oaks in southern Arizona
(Gilbertson et al 1974).
Armillaria nabsnona
Armillaria nabsnona is found on many
hardwoods in western North America,
most commonly on alder. Macroscopic
characters that distinguish A. nabsnona
from other North American species
of Armillaria include a deeper orange
coloration when fresh and a narrower
stipe in comparison to the size of the
cap. The stipe is darker than other Ar-
millaria species, especially when dried.
There are no scales, but small black
hairs may be present on the surface of
the pileus, as for A. mellea. Armillaria
nabsnosa is often associated with dead
wood in riparian zones and causes a
white rot (Volk et al. 1996). In Califor-
nia, it is restricted to the northwestern
redwood forest area and is primarily
associated with living and dead red
alder (Alnus rubra), tanoak (Lithocar-
pus densiflorus) and California laurel
(Umbellularia californica) (Baumgartner
and Rizzo 2001b).
Armillaria solidipes(= Armillaria
ostoyae)
Armillaria solidipes is the most com-
mon species of Armillaria in Arizona
(M. Fairweather, personal communi-
cation). It is usually associated with
conifers but will also colonize hard-
woods and causes a serious root- and
butt-rot. In some areas it seems to be
nonpathogenic (Klopfenstein et al.
2008) but may become an opportu-
nistic pathogen on trees stressed by
drought, insect attack or other factors.
Armillaria solidipes can be differenti-
ated from other species of Armillaria
by its brown cap and stipe, the fairly
prominent scales on the cap, and the
well-developed ring (annulus). Mush-
rooms form in clusters at the base of
affected trees and on the dead wood
of fire scars and other wounds. The
wood becomes yellow to brown in
color and advanced decay appears
water-soaked and stringy.
Bjerkandera adusta
“Smoky Polypore.” Fruiting body ef-
fused-reflexed (growing flat against
the surface, but with a shelflike edge)
to sessile (stalkless), or shelf-like,
up to 3 cm wide, frequently in large
numbers or coalescing to form larger
fruiting bodies or even large sheets
on the underside of logs. The upper
surface is pale yellow-white to pale
creamy-buff, becoming grayish-white
with age, smooth to finely fuzzy. The
pore surface is pale gray to dark gray,
sometimes with a brown tint. Pores
are 5 – 7 per mm, circular, gray, and
become angular with age. This fungus
causes a whiterot of fallen wood, slash
and standing snags of hardwoods,
more rarely on conifers, and is very
common in old aspen stands (Gilb-
ertson and Ryvarden 1986). In Ari-
zona, it is reported on Arizona alder,
trembling aspen (Populus tremuloides),
Gambel oak (Quercus gambelii), as well
as southwestern white pine (Pinus
reflexa) and Douglas-fir (Pseudotsuga
menziesii) (Gilbertson et al. 1974).
Coniophora species
Fruiting bodies are thin, brown, and
resupinate (flattened) with an ir-
regular, wrinkled surface. There are
no pores or teeth. The margin of the
fruiting body is white and fringed.
Mycelial cords may also be seen;
these conduct water and allow the
fungus to grow in relatively dry areas.
Traditionally based on microscopic
features, four common species were
recognized in North America. Recent
molecular studies show a high degree
of genetic variability and a large
number of cryptic species separable
only by DNA sequence (Kaserud et al.
2007). Species of Coniophora form root
and butt rots of living conifers but are
largely saprotrophic on hardwoods.
They are brown-rotters and form a
brown, cubical rot that sequesters
carbon into the soil for long-term
storage (USDA Forest Service 2011).
In Arizona, Coniophora species have
been associated with alder, walnut,
sycamore, and trembling aspen (Gil-
bertson et al. 1974).
Daedaelopsis confragosa
“Thin-walled Maze Flat Polypore.”
Fruiting bodies are annual but per-
sistent, bracket-like, 2.5 – 15 cm wide,
upper surface convex to flat with a
thin, sharp margin, usually zonate,
and may have matted hair on the
surface or be smooth. They are gray
to brown or reddish brown. The pore
Armillaria nabsnona trudell
Bjerkandera adusta
Coniophora puteana
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surface is poroid to maze- or gill-like,
white to brownish, pink when buised.
This fungus is extremely variable
in appearance. It forms a whiterot
on dead wood of many hardwood
genera, more rarely on conifers. It
is infrequent in the West and more
common in the Northwest (Gilbertson
and Ryvarden, 1986). In Arizona, it
has been reported on Arizona alder
(Alnus oblongifolia), Bigtooth maple
(Acer grandidentatum), white fir (Abies
concolor) and Douglas-fir (Pseudotsuga
menziesii) (Gilbertson et al., 1974).
Ganoderma applanatum
“Artist’s Conk.” Fruiting body is
perennial, 5 – 52 cm wide or even
larger, convex, hoof-shaped to fan-
shaped, sessile. The upper surface is
hard, concentrically zonate and fur-
rowed, gray to brown in color. The
spore-bearing surface is poroid (pores
clearly visible), white at first, becom-
ing off-white to dingy yellow with
age, staining brown upon bruising
(the characteristic used by artists for
etching). Pores are very small, 4 – 6
per mm. This fungus is very common,
and may be solitary or in overlapping
clusters on stumps, logs, or wounds
of living trees (Binion et al. 2008). It
forms a mottled whiterot of roots,
root crown and trunks. In the East,
the presence of conks can be cause
for immediate removal of the affected
tree as conks are often associated with
advanced decay and potential fail-
ure (Luley 2005), and are frequently
observed on stumps and fallen logs.
In some parts of the West, conks are
most frequently observed on big leaf
maple (Acer macrophyllum) and bay
laurel (Umbellularia californica) where
they are not associated with advanced
decay (D. Shaw personal commu-
nication). In Arizona, it is found
almost exclusively on live aspen as
a root and butt rot (M. Fairweather
personal communication; Gilbertson
and Ryvarden 1986). The fungus of-
ten enters a tree through wounds in
exposed roots and base of tree. Decay
commonly extends 1 – 2 m above
and below the fruiting body. Decline
and mortality are more pronounced
during periods of environmental
stress. Ganoderma brownii, which is
more hoof-shaped and has an orange
pore surface, is a closely related, but
uncommon, species that occupies a
similar niche in California (Swiecki
and Bernhardt 2006). In Arizona, G.
applanatum is primarily associated
with trembling aspen as a root and
buttrot (Gilbertson et al. 1974).
Ganoderma lucidum
“Reishi,” “Varnish Conk.” Fruit-
ing body annual, 2.5 – 3.5 cm wide,
semi-circular to fan-shaped or kid-
ney-shaped, surface with concentric
zones and furrows, shiny, dark red,
reddish-brown to orange-brown be-
coming ochre or yellow toward the
margin. The stipe is lateral, 2.5 – 10 cm
long and 0.5 – 4 cm thick. The spore-
bearing surface is poroid, off-white to
yellow initially, becoming brown with
age or upon bruising. Pores are small,
4 – 7 per mm (Binion et al. 2008). This
fungus causes a white root and butt
rot of living native hardwoods and ex-
otic ornamental hardwood trees and
shrubs. Fruiting bodies develop at or
near the ground line (Gilbertson and
Ryvarden 1986). The fungus is found
in California and the Southwest but
not the Rocky Mountains or Pacific
Northwest (Swiecki and Bernhardt
2006). In the Southwest, Ganoderma
root rot causes the gradual decline and
death of mature Fremont cottonwood.
Fruiting bodies develop at the base of
the tree during the rainy season (Ol-
sen 1998). In Arizona, it has also been
reported on river she-oak (Casuarina
cunninghamiana), netleaf hackberry
(Celtis reticulata), loquat (Eriobotrya
japonica), Modesto ash, European ol-
ive (Olea europea),Arizona sycamore,
Emory oak (Quercus emoryi), silverleaf
oak (Quercus hypoleucoides),African
sumac (Rhus lancea), and Peruvian
peppertree (Schinus molle)(Gilbertson
et al. 1974). In California, fruiting bod-
ies generally do not form until there
is extensive decay with an elevated
risk of failure (Swiecki and Bernhardt
2006). This is in contrast to the eastern
and Midwestern United States where
the presence of fruiting bodies alone
is usually not reason for tree removal
(Luley 2005). The closely related var-
nish conks, Ganoderma tsugae and G.
oregonense, are found on conifers.
Daedaelopsis confragosa — top Daedaelopsis confragosa — gills
Ganoderma applanatum Bjerkandera adusta
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Gloeophyllum sepiarium
The fruiting bodies are annual to
perennial, broadly sessile, up to 7 cm
wide, 12 cm long and 6 – 8 cm thick
at the base of the pileus, semicircular
or rosette-shaped, often in clusters
from a common base or fused later-
ally. The top of the fruiting body is
initially a bright orange-brown but
darkens with age to reddish brown
and finally gray to black. The pore
surface is pale brown, darkening with
age. The pores resemble parallel gills
(lamellae) mixed in with pored areas
of variable size. This fungus causes
a brown rot of dead hardwoods and
conifers; ubiquitous throughout
North America. It is quite resistant to
high temperatures and dry conditions
and can be found frequently on case-
hardened logs throughout the West.
It is more commonly associated with
conifers, but is also present on alder,
birch (Betula), hawthorn (Cratageus),
poplar, cherry (Prunus), willow, and
especially aspen. It is one of the most
important brown-rot fungi in the
creation of coarse woody debris (Gil-
bertson and Ryvarden 1986).
Gloeoporus dichrous
Fruiting bodies are annual, resupinate
(flat) to pileate (with a cap), often
effuse-reflexed, usually clustered in
shelves. Soft when fresh but resinous
and hard when dry. Caps are narrow
with a white to cream upper surface
and rarely above 4 cm wide, 10 cm
long, and 5 mm thick at the base. The
pore surface is initially light reddish,
darkening to purple and brown with
age. Pores are round to angular, 4 – 6
per mm, often quite shallow and ap-
pear more like a reticulated network
than a traditional pore structure. This
fungus is easy to recognize because
of its deep reddish pore surface and
the white, cottony pileus and context.
The pore surface is gelatinous to rub-
bery and can be peeled away from the
rest of the fruiting body with a finger
nail when fresh. It causes a white
rot on dead wood of many different
hardwoods and may also be found
on dead conifers. It can even fruit on
top of other polypores. This fungus is
widely distributed throughout North
America (Gilbertson and Ryvarden
1986). In Arizona, G. dichrous occurs
on Arizona sycamore and a variety of
oak species (Gilbertson et al. 1974).
Hericium americanum
Fruiting bodies are large, up to 25
cm in diameter, and are composed
of many branches with long white
spines hanging down from the branch
tips. Young specimens are white but
age to yellow. The fruiting body is at-
tached to the wood with a stout, thick
stalk. It forms a white rot on the logs
and standing trunks of hardwoods
and conifers (Binion et al. 2008). In
Arizona, it is associated with aspen
(M. Fairweather personal communi-
cation).
Inonotus arizonicus
Basidiocarps form on the main trunk
of trees or in large basal cavities. The
fruiting bodies are annual, effused or
effused-reflexed, up to 10 cm wide, 16
cm long, and 8 cm thick at the base,
ungulate (hooflike) to applanate (flat-
tened and spreading) with either a
single pileus or several pilei stacked
on top of each other. The upper and
lower surfaces of the fruiting body are
brown, with the pore surface bruising
darker with handling. The pores are
Gloeophyllum sepiarium — top
Gloeoporus dichrous — top
Gloeophyllum sepiarium — bottom
Gloeoporus dichrous — bottom
Hericium americanum
Inonotus arizonicus
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angular, 3 – 5 per mm (Gilbertson and
Ryvarden 1986). This fungus is the
primary cause of heartrot of living
Arizona sycamore in Arizona, New
Mexico and California (Goldstein
and Gilbertson 1981). The decay is a
uniform white rot; brown thread-like
masses may be present in advanced
stages of decay. The fungus can con-
tinue to decay wood saprotrophically
after tree death and may form fruiting
bodies on dead standing and fallen
trees. The fungus is common but only
within the Southwest (Gilbertson and
Ryvarden 1986).
Inonotus hispidus
“Shaggy Polypore.” Fruiting body
shelflike, dimidiate (semi-circular)
broadly attached, usually solitary, up
to 10 cm wide by 15 cm long by 8 cm
thick at the base. Top, including the
edge, is reddish orange, becoming
reddish brown to nearly black with
age, no zonations, but with many
coarse hairs when young (“hispid”).
Pore surface is yellow-brown be-
coming dark brown with age. Pores
are angular, 1 – 3 per mm, becom-
ing eroded and uneven. The fungus
causes a white heartrot and saprot of
living hardwoods and is commonly
associated with trunk cankers on oaks.
In Arizona, it is a major decay fungus
of Arizona walnut and may often be
found in association with Phellinus
weirianus. It is quite common to see
both fungi fruiting on the same tree
(Gilbertson and Ryvarden 1986). Ino-
notus hispidus also occurs on boxelder
(Acer negundo), California buckthorn
(Rhamnus californica), and several spe-
cies of oak (Gilbertson et al. 1974).
Inonotus munzii
Fruiting bodies are sessile, often
in large clusters on the trunk, ap-
planate to hoof-shaped, 20 cm wide
by 30 cm long by 6 cm thick at the
base. The upper surface is initially a
bright yellow brown becoming red-
dish brown with age. Pore surface is
a yellow brown with angular pores,
2 – 4 mm/diameter. Inonotus munzii
causes a major white heartrot of living
hardwoods and continues to decay
dead standing trees and stumps. It is
one of the main decay fungi of willow
and cottonwood in the Southwest. It
is also common on California pepper
tree (Schinus molle), white mulberry
(Morus alba) and many ornamentals in
southern AZ (Gilbertson and Ryvar-
den 1986). Inonotus heartrot is often
associated with water-stressed trees
or wounds. The fungus is not consid-
ered a primary pathogen, but stressed
trees will decline over many years.
Branch dieback is common and large
dead branches should be removed in
populated areas (Olsen 1998).
Laetiporus gilbertsonii
Fruiting bodies forming clusters of
overlapping shelves, up to 20 cm
wide, with a lateral narrow or wide
stipe or sessile. Upper surface can be
pale salmon-orange or pale pinkish-
orange to tan or light brown in age,
sometimes nearly white. Pore surface
is lemon-yellow to pale lemon-yel-
low. Pores are initially circular,
becoming more angular with age, 2
– 4 per mm, present along the stipe
to the attachment point. This fungus
causes a brown rot of hardwoods in
the Southwest and is often associated
with oak and eucalypts such as blue
gum (Eucalyptus globulus) in living
trees, dead trunks, and logs (Burdsall
and Banik 2001). In Arizona, Laetipo-
rous gilbertsonii has been observed on
Modesto ash (M. Fairweather per-
sonal communication). The decay is a
cubical brown heartrot that may lead
to failure in the main stem or butt.
Decay may progress into major roots
(Luley 2005). The presence of Laetipo-
rus fruiting bodies is often an indica-
tor of extensive decay and should be
taken seriously. Laetiporus gilbertsonii
Inonotus hispidus
Inonotus munzii — close-up Inonotus munzii — distance
Inonotus gilbertsonii
46
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var. pallidus is similar but has a pale
orange to pale brown pileus surface
and a white pore surface. Laetiporus
conifericola grows only on conifers
(Burdsall and Banik 2001).
Perenniporia fraxinophila
Fruiting bodies are sessile, resupinate
or effused-reflexed, either single or
in clusters, hoof-shaped, up to 7 cm
wide, 9 cm long, and 7 cm thick at
the base. The upper surface is usu-
ally grayish-black. The pore surface is
ivory to buff with circular to angular
pores, 3-5 per mm. Perenniporia frax-
inophila causes a white trunk rot of
living ash trees and is also on other
hardwoods as well as juniper. It is
found throughout North America in
the range of ash with the exception of
the Pacific Northwest and Gulf Coast.
It is very common on Modesto ash in
Arizona and New Mexico (Gilbertson
and Ryvarden 1987)
Phellinus everhartii
Fruiting body is perennial, sessile,
and hoof-shaped, up to 6 cm wide, 13
cm long, and 8 cm thick at the base.
The upper surface of conk is dark
brown to black, velvety when young
but becoming smooth and eroded
with age. The spore bearing surface
is poroid with a velvety appearance,
dark chocolate brown, pores circular
to angular, 5-6 per mm. It causes a
white heartrot of living hardwoods,
primarily on oak and also on walnut
(USDA Forest Service 2013; Gilbertson
and Ryvarden 1987). There are several
other similar species that are difficult
to distinguish without a microscope.
It is common in the Southwest (Gilb-
ertson and Ryvarden 1987).
Phellinus gilvus
“Mustard Yellow Polypore.” Fruiting
body annual to perennial, sessile or
slightly effused-reflexed, solitary or
shelving in large numbers, up to 7 cm
wide, 12 cm long, and 3 cm thick at
the base. This fungus is quite variable
in appearance. The upper surface is
dark yellow-brown to rusty brown,
velvet when young, becoming smooth
with age, tapering to a sharp margin.
The spore-bearing surface is poroid,
reddish brown to dark purple brown,
with circular to angular pores, 1 – 5
per mm (Binion et al. 2006). Phellinus
gilvus causes a white rot of heartwood
of living oaks and a uniform white
rot of dead wood of many hardwood
species (Gilbertson and Ryvarden
1987). It is the most common conk on
oak and tanoak in California (Wood
2010). In Arizona, it occurs on alder,
ash, walnut, sycamore, cherry, oak,
mesquite (Prosopis juliflora), and
Gooding’s willow (Salix gooddingii)
(Gilbertson et al. 1974).
Phellinus weirianus
Fruiting body is sessile and usually
hoof-shaped, up to 30 cm wide by 20
cm long by 15 cm thick at the base.
The upper surface darkens to black
with age but has a golden brown mar-
gin. The pore surface is bright golden
brown with small, circular pores 5 – 7
per mm. This fungus is found exclu-
sively on Juglans, especially Arizona
walnut (J. major), in the southwestern
U.S. and Mexico. It forms a white
heartrot of living walnut (Gilbertson
and Ryvarden, 1987) and is frequently
found in association with Inonotus
hispidus.
Pleurotus ostreatus complex
“Oyster mushroom.” The Pleurotus
ostreatus complex is highly variable
and contains many cryptic species
that share morphological character-
istics and have overlapping ranges.
Early work (Vilgalys et al. 1993)
differentiated 3 intersterility groups
which corresponded to Pleurotus os-
treatus (Group I), Pleurotus pulmonar-
ius (Group II) and Pleurotus populinus
(Group III). Pleurotus populinus is as-
sociated only with poplar and cotton-
wood. In this same paper, however,
the vouchered specimen collected in
a study on aspen-decaying fungi from
Arizona (Lindsey and Gilbertson
1978) was Pleurotus ostreatus. It was
noted that P. pulmonarius can also be
Perenniporia fraxinophila
Phellinus everhartii
Phellinus gilvus
Phellinus weirianus
Arborist
47
WESTERN
Fall 2013
found on aspen and other Populus
species, although it tends to favor
higher, drier sites while P. ostreatus is
more frequently associated with low-
land areas along rivers and streams.
These fungi are easily recognized as
large, fleshy, white-to brown- to lilac-
colored fruiting bodies that are select
edibles. They tend to be gray to white
and relatively thin-fleshed on oaks to
thick fleshed, grey-brown shelves on
cottonwood and willow. The cap can
be 5 – 25 cm in diameter, convex to
nearly flat at maturity with a margin
that is lobed to wavy, especially when
young. Surface of the cap is smooth.
The gills are white, sometimes be-
coming yellowish with age. The gills
continue onto the upper portion of
the stalk, when present. The stalk
is often absent but when present is
short and thick, 0.5-3.0 cm long, 0.5-
2.0 cm thick, eccentric or lateral with
dense white hairs at the base. The
fruiting body may have the odor of
anise when fresh. It is usually found
in a cluster of overlapping shelves on
logs and boles of hardwoods. Fruiting
begins in early fall and may continue
through winter in the mild climates
of California (Wood 2010). These
fungi are all white-rotters and can
be opportunistic pathogens (Dr. D.
Rizzo personal communication).On
cottonwood, Pleurotus sp. can cause
a root and stem rot, resulting in tree
decline, suppression, crown thinning,
and eventual death (USFS 1975).
Polyporus species
The genus Polyporus is a large group
of poroid fungi with a central to lat-
eral stipe. Most species have a light
to deep brown upper surface, are
tough when fresh but woody when
dried. Some of the common species
are: P. arcularius, a smallish polypore
(up to 4 cm wide) with a central stipe
and radially arranged hexagonal
pores; P. badius (= Royoporus badius),
a fairly large (up to 15 cm broad) but
thin polypore with a central or lateral
stipe that is black and minutely hairy
at its base; and P. brumalis, which is of
medium size (up to 8 cm wide) with
a central or lateral stipe and angular
pores. All cause white rots of woody
debris and dead trees (Binion 2008;
Gilbertson and Ryvarden 1987).
Pycnoporus cinnabarinus
Fruiting bodies are annual, sessile
to effused-reflexed, nearly round to
elongated, rather leathery when fresh,
and up to 7 cm wide, 13 cm long, and 4
cm thick at the base. The upper surface
is reddish to apricot orange, lighter or
darker with age. The pore surface is
red and stays reddish longer than the
upper surface. The pores are circular
to angular, 3-4 per mm. This fungus
forms a white rot of dead hardwood
logs and stumps occurring only rarely
on conifers. It is found throughout
North America, including Alaska, and
Canada (Gilbertson and Ryvarden
1987). In Arizona, it is associated with
Freemont cottonwood, spiny cholla
(Opuntia spinosior), Emory oak, and
several species of pines (Gilbertson
et al., 1974).Pycnoporous sanguineus
is similar but the fruiting bodies are
thinner, more brightly colored, and
shiny (Kuo2010). It is also associated
with a white rot of dead hardwoods.
In Arizona, Pycnoporus sanguineusis
primarily in the southern portion
of the state and has been reported
on Arizona walnut (Juglans major),
Goodding’s willow (Salix gooddingii),
and Emory oak (Quercus emoryi) (Gil-
bertson et al., 1974).
Rigidoporous ulmarius
The fruiting bodies of this fungus
are often very inconspicuous under
exposed roots or in hollow, decayed
areas at the base of trees. They can
often be located by the heavy accu-
mulation of white spores deposited
nearby (Gilbertson et al. 1974). The
fruiting bodies are perennial, sessile,
effused-reflexed, and up to 9 cm wide,
Pleurotus ostreatus
Polyporus arcularius Polyporus arcularius - pores Pycnoporus cinnabarinus
Rigidoporous ulmarius
48
Arborist
WESTERN
Fall 2013
Arborist
WESTERN
30 cm long, and 6 cm thick at the base.
The upper surface is buff to cream
colored and often contains plant litter
when it develops under roots or be-
low the soil surface. The pore surface
is pinkish buff when fresh, drying to a
pale, brownish pink or darker brown.
The pores are angular, 5 – 6 per mm
and may require a hand lens to see.
This fungus forms a yellow, stringy
root and butt rot in living hardwoods
and can continue to decay the wood
after the tree is dead. It is very com-
mon on Fremont cottonwood (Populus
fremontii) in Arizona and is found
throughout the southern U.S. and
Central America (Gilbertson and
Ryvarden 1987).
Schizophyllum commune
“Split-gill Fungus.” Fruiting bodies
are leathery, fan-shaped brackets,
1 – 3.5 cm in diameter, frequently
lobed or fused at the base with other
brackets. The upper surface is densely
hairy, light grayish-brown when
moist but ashy grey to white when
dry. The lower surface is light gray
and consists of well-spaced, longitu-
dinally split gills. The stipe is usually
absent. The flesh is thin, light grey to
brown, and tough. This fungus can be
found year-round, usually in clusters,
on dead boles and branches. (Wood
2010). It causes a white rot of dead
hardwoods. In Arizona, it has been
reported on Modesto ash (Fraxinus
velutina ‘Modesto’) and Goodding’s
willow (Salix gooddingii) (Gilbertson
et al. 1974).
Steccherinum ochraceum
Fruiting bodies are annual, broadly
effuse, often resupinate or effuse-re-
flexed with a narrow pileus. They are
tightly attached to the substrate. In-
dividual patches sometimes coalesce
to form very large fruiting bodies
over the entire undersurface of major
branches. The upper surface, when
present, is wooly and white to gray
to tan. The spore-bearing surface is
orange to tan to slightly pinkish cin-
namon and borne on spines up to
2 mm long. The margin of fruiting
body is white and without spines.
Steccherinum ochraceum is common
on dead wood of many different
hardwood trees (Binion et al. 2008).
In Arizona, it has been reported on
Arizona alder (Alnus oblongifolia),
Arizona walnut (Juglans major), and
blue spruce (Picea pungens) (Gilbert-
son et al. 1974).
Trametes species
The genus Trametes contains many
common saprot fungi with broad
host and geographical ranges. The
group is characterized primarily by
microscopic characteristics – the po-
roid fruiting bodies are formed from
three different types of fungal hyphae
which give them a characteristically
hard, leathery texture. Trametes versi-
color, the “Turkey Tail Fungus” has a
zonate, multicolored upper surface
varying from hairy to smooth or vel-
vety in narrow concentric zones. It
often forms large clusters of shelves.
Trametes cervina is only faintly zonate
and with much more subdued colors
on the upper surface - predominantly
shades of pinkish buff to cinnamon-
buff or clay color – with coarse, stiff
hairs. The pore surface is cinnamon-
buff, becoming a darker brown with
age. Pores are irregular, up to 1 mm
in diameter and eventually split,
forming tooth-like structures. All of
these fungi are strong white-rotters
(Gilbertson and Ryvarden 1987).
Trametes versicolor can attack and colo-
nize cambium adjacent to dead wood
and form cankers. The presence of
Trametes and other saprot fungi is an
indication that the branch or section of
trunk is dead and decayed. Sanitation
pruning to remove infected branches
is recommended since some of them
can infect and colonize healthy tissue
(Luley 2005).
Trichaptum biforme
“Violet-toothed Polypore.” Fruiting
bodies are annual, sessile or effused-
reflexed, solitary or shelving, often
coalescing to form large sheets. They
Schizophyllum commune — top Schizophyllum commune — gills
Steccherinum ochraceum
Trametes cervina
Arborist
49
WESTERN
Fall 2013
Steve Trudell, Michael Wood (http://
www.mykoweb.com), and Thomas
J.Volk (http://TomVolkFungi.net).
Please contact senior author for per-
mission to use photographs from this
paper.
Jessie A. Glaeser, USFS, Northern
Research Station, Madison, WI
53726 (jglaeser@fs.fed.us) and
Kevin T. Smith, USFS, Northern
Research Station, Durham, NH
03824 (ktsmith@fs.fed.us)
a white pocket rot of sapwood. The
wood becomes lacy and fragile with
small empty pockets (Gilbertson and
Ryvarden 1987). Trichaptum abietinum
is similar, but grows on conifers.
Photo credits: Photos used with per-
mission and thanks from Ettore Baloc-
chi, Harold H. Burdsall, Jr., Whitney
Cranshaw, Mary Lou Fairweather,
Jessie A. Glaeser, Larry Grand, Steven
Katovich, Andrew Khitsun (http://
www.wisconsonmushrooms.com),
can be up to 6 cm wide and 3 mm
thick at the base. The upper surface
is gray to tan, hairy to smooth, with
concentric zones of thick and thin
woolliness. Pore surface is purple to
pink, especially at the margins, but
becoming brown with age. Pores are
initially angular, 3 – 5 per mm, but
eventually erode and split to form
tooth-like structures. This fungus is
very common on fallen woody de-
bris, logs and stumps of hardwoods
(Binion et al. 2008) where it forms
Trametes versicolor Trichaptum biforme — bottomTrichaptum biforme - top
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Arborist
WESTERN
Fall 2013
Arborist
WESTERN
References
Baumgartner, K. and Rizzo, D.M. 2001a. Distribution of Armillaria species in California.Mycologia 93: 821-830.
Baumgartner, K. and Rizzo, D.M. 2001b. Ecology of Armillaria spp. in mixed-hardwood forests of California. Plant Dis. 85:
947-951.
Binion, D.E., Stephenson, S.L., Roody, W.C., Burdsall, H.H., Jr., Vasilyeva, L.N., and Miller, O.K., Jr. 2008.Macrofungi of
Oak. Morgantown, WV: West Virginia University Press. 467 pp.
Burdsall, H.H. Jr. and Banik, M.T. 2001. The genus Laetiporus in North America. Harvard Papers in Botany 6: 43-55.
Burdsall, H.H. Jr. and Volk, T.J. 1993. The state of taxonomy of the genus Armillaria. McIlvainea 11:4-12.Modified version
available at http://tomvolkfungi.net (accessed 05-26-2010).
Cowling, E.B., 1961: Comparative biochemistry of the decay of sweetgum sapwood by white-rot and brown-rot fungi. U.S.
Dep. Agric. Tech. Bull. No. 1258, pp. 1–75.
Gilbertson, R.L., Martin, K.J., and Lindsey, J.P. 1974. Annotated check list and host index for Arizona wood-rotting fungi.
Technical Bulletin 209. Tucson, AZ: Agricultural Experiment Station, University of Arizona, Tucson. 48 pp.
Gilbertson, R.L. and Ryvarden, L. 1986: North American Polypores. Vol. 1. Oslo: Fungiflora. 1-433.
Gilbertson, R.L. and Ryvarden, L. 1987: North American Polypores. Vol. 2. Oslo: Fungiflora. 437-885.
Goldstein, D. and Gilbertson, R.L. 1981. Cultural Morphology and Sexuality of Inonotus arizonicus. Mycologia 73:167-180.
Highley, T.L. and Kirk, T.K. 1979: Mechanisms of wood decay and the unique features of heartrots. Phytopathology 69(10):
1151- 1157.
Kauserud, H., Shalchian-Tabrizi, K., Decock, C. 2007. Multilocus sequencing reveals multiple geographically structured
lineages of Coniophora arida and C. olivacea (Boletales) in North America. Mycologia 99: 705-713.
Klopfenstein, N.B., Hanna, J.W., Fairweather, M.L., Shaw, J.D., Mathiasen, R., Hoffman, C., Nelson, E., Kim, M.S., Ross-
Davis, A.L. 2011.Developing a prediction model for Armillaria solidpes in Arizona. In: Zeglen, S. and Palacios, P. [eds]. Pro-
ceedings of the 59th Annual Western International Forest Disease Work Conference; 2011 October 10-14; Leavenworth, WA.
Kuo, M. 2010.Pycnoporus cinnabarinus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.
com/pycnoporus_cinnabarinus.html (accessed 04-23-2013)
Lindsey, J.P. and Gilbertson, R.L. 1978. Basidiomycetes that decay aspen in North America. Germany: J. Cramer. 406 pp.
Luley, C. J., 2005: Wood Decay Fungi Common to Urban Living Trees in the Northeast and Central United States. Naples, NY:
Urban Forestry LLC. 60 pp.
Manion, P.D. (2003) Evolution of concepts in forest pathology. Phytopathology 93: 1052–1055.
Olsen, M. 1998. Extension Plant Pathology – Plant Disease Identification. University of Arizona, Tucson.[Available at http://
ag.arizona.edu/PLP/plpext/index.html (accessed 04-10 -013)].
Shigo, A.L. 1984. Compartmentalization: a conceptual framework for understanding how trees grow and defend themselves.
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Shortle, W.C., Smith, K.T., and Dudzik, K.R. 1996: Decay diseases of stemwood: Detection, diagnosis, and management. In:
Forest Trees and Palms. Ed. by Raychaudhuri, S.P.; Maramorosch, Karl, New Delhi, India: Oxford & IBH Publishing: 95-109.
[Available at http://www.nrs.fs.fed.us/pubs/5514 (accessed 04-24-2013)].
Smith, K.T. 2006.Compartmentalization today. Arboricultural Journal 29, 173-184.
Swiecki, T.J. and Bernhardt, E.A. A Field Guide to Insects and Diseases of California Oaks. PSW-GTR-197. Washington D.C.:
U.S. Forest Service, Pacific Southwest Research Station. 152 pp.
Tainter, F.H. and Baker, F.A. 1996: Principles of Forest Pathology. New York: John Wiley and Sons. 805 pp.
Toupin, R., Filip, G., Erkert, T., Barger, M. 2008. Field Guide for Danger Tree Identification and Response. R6-NR-FP-PR-
01-08. Washington, DC: U.S. Forest Service. 64 pp.
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butt rot. http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5353724.pdf (accessed 04- 15-2013).
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Volk, T.J., Burdsall, H.H. Jr., and Banik, M.T. 1996. Armillaria nabsnona, a new species from western North America.Mycolo-
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Arborist
51
WESTERN
Fall 2013
Pathogenic wood decay fungi can
be further subdivided into two
categories based on the position
of the fungus within the liv-
ing tree and type of wood they
degrade. Name them: __________,
______________________________
Fruiting bodies of saprot fungi
around the outer circumference of
the stem usually do not indicate
structural weakness because the
decay is superficial. T or F?
Early-seral tree species generally
strongly resist the spread of infec-
tion after the wounding of live
sapwood.T or F?
Dead wood of early-seral tree
species, including the dead wood
attached to living trees, is general-
ly of low durability and therefore
decays readily. T or F?
Early-seral tree species in highly
trafficked areas are of special
concern because they are typically
weak compartmentalizers. T or F?
White mycelial fans under the
bark of diseased roots and the
root crown often associated with
clusters of gilled mushrooms in-
dicate what genus of root rotting
fungi? ________________________
Fruiting bodies are variable, but
upper the surface is dark yel-
low-brown to rusty brown and
velvet when young; it is the most
common conk on oak and tanoak
in California, causing a white rot
of heartwood of living oaks and a
uniform white rot of dead wood
of many hardwood. This best
describes what fungus? _________
A common saprot fungus that can
invade living sapwood. Fruiting
bodies are hard, and leathery and
often found in clusters on branch-
es or dead tissue. The upper
surface is zonate multicolored,
somewhat resembling a turkey’s
tail. This best describes what fun-
gus? _________________________
12.
13.
14.
15.
16.
17.
18.
19.
Home study
for CEUs
You may receive one hour
of Certified Arborist and/
or WCISA Certified Tree
Worker continuing education
units (CEUs) for reading the
following article and complet-
ing the test questions. Copy
the question pages and use it
to record your answers. Darken
the correct letter choices and
circle your choice for true and
false or correct choice ques-
tions. Each question has only
one correct answer. Passing
score for this test is 15 correct
answers (80%).
Next, complete the registra-
tion information on this form
and send it to:
WCISA Administrative Office
31883 Success Valley Dr.
Porterville, CA 93257
559-784-8711 fax
Note: If 80 percent or greater
of the questions have been
answered correctly, the ISA
will be notified of the CEU
assignment for Certified Arbor-
ists and it will be posted by
the ISA. The Western Chapter
will post the CEU for Certified
Tree Workers. If a passing score
is not achieved, the test will
be returned for corrections.
No CEU confirmations will be
sent to you.
Registration Information
Name: __________________
Cert. # __________________
Address: _______________
City: ____________________
State: ______ Zip: ________
Home study for CEUs: Decay fungi of riparian
trees in the Southwestern U.S.
Fall, September 30, 2013 — Expiration date for submitting answer sheet is
October 1, 2014.
The CEUs from this article can only be applied to the 3-
year current certification period.
Riparian forests are prone to in-
jury and infection by wood decay
fungi due to frequent disturbance
events. T or F?
Scientists are now relying more
on DNA sequence analysis rather
than traditional groupings of
organisms on the basis of shared
morphological similarities to
establish genetic relationships
among fungi and other organ-
isms. T or F?
Observations based on fungal
habitat, spatial position (location
in tree), and the appearance of the
decayed wood is of little value to
risk assessment specialists. T or F?
White / brown rot fungi degrade
the cellulose and hemicellulose
in the wood cell wall, but do not
significantly degrade the lignin.
(circle correct choice)
Brown-rotted wood in advanced
decay is often seen as cubical
fragments. T or F?
White-rot fungi are more fre-
quently associated with hard-
woods / conifers and brown rot
fungi are more frequently associ-
ated with hardwoods / conifers
(circle correct choices)
Many small pockets of decay
throughout the infected volume
of wood, describes a type of rot
known as? ____________________
Significant strength loss occurs
early in the decay process when
white rot fungi are involved.
T or F?
Loss of wood strength occurs
gradually when brown rots are
involved. T or F?
Wood decay fungi that attack
wood in service or as felled logs,
slash, or dead trees are referred to
as ____________________________
Wood decay fungi that can attack
woody tissue of living trees are
called? _______________________
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
