Morel Mushrooms, Macrofungi, Corticolous Myxomycetes, And American Elm Trees
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Morel Mushrooms, Macrofungi,
Corticolous Myxomycetes,
And American Elm Trees
Harold W. Keller
Botanical Research Institute of Texas, 1700 University Drive, Fort Worth, TX 76107-3400; haroldkeller@hotmail.com
Abstract: the University of Iowa. American elm structure and external slime sheaths.
cultures recently led to the discovery Key Words:
Ulmus americana (American elm)
of new species of Mycena, corticioid Licea species, moist chamber bark
occurs in Texas and mostly has escaped
crust fungi represented by species of cultures, Morchella species, Ophiostoma
the pathogenic fungus Ophiostoma ulmi
Dendrothele, and myxomycete life cycle ulmi, slime molds, Ulmus americana.
and O. novo-ulmi, the causative agents stages. Many corticolous myxomycete
of Dutch elm disease. The American species in the genus Licea are small in Introduction
elm is a beautiful ornamental shade the 100–200 µm range, easily overlooked The demise of American elm trees
tree that was planted in cities and in moist chamber bark cultures from begins in my hometown Peabody,
towns throughout the Midwest as a living trees, and often are species new Kansas in the 1950s, and continued
monoculture, facilitating the spread to science, for example, Licea iridescens into the 1960s and 70s at the University
of Dutch elm disease by the elm bark recently described. Photographic of Iowa. Although the pathogen for
beetle insect vector and by root grafts. images of rare and undescribed tiny Dutch elm disease had been around
The association between dying elm trees myxomycete species are shown using long before then, the devastation and
and morel mushrooms is described from multi-focus imaging and computerized removal of American elm trees was
Texas to Iowa and Ohio. Described here stacking giving greater depth of field visually most dramatic in Iowa City
is the early history of moist chamber and three-dimensional detail. The when I was a Ph.D. student studying
cultures using American elm tree importance of myxomycete stalks is myxomycetes with Professor George
trunk bark collected in the 1930s at discussed especially in regard to internal W. Martin at the University of Iowa.
Fig. 1. Photo by Harold W. Keller. Dead American elm trees with V-shaped branching pattern.
Spring 2021 FUNGI Volume 14:2 23
A
merican elm were widely seen myxomycetes were abundant, especially footed morel” (Morchella "crassipes")
on the campus and lined the Perichaena chrysosperma, P. depressa, was found (12–14 inches in height with a
streets in Iowa City. More and Licea biforis on the underside of the stalk 5 inches in length and 2.4 inches in
than 2,000 American elms once grew bark separating from the woody tree width). This “species” is now considered
on the University of Iowa campus trunk. This was a massive fruiting of simply an older developmental phase of
but were eventually ravaged by the Licea biforis represented by thousands M. americana and not a distinct species
Dutch elm fungal pathogen so that of date-shaped, orangish sporangia with (Keller, 1998).
only two survived. Apparently one their distinctive longitudinal slit-like Morels assigned to Morchella
tree that survived was located on the dehiscence and bright yellow spore americana have been found by David
campus Pentacrest. It was a towering mass. (Fig. 2). Lewis, March 12, 2005 in Edwards
giant estimated to be about 15 feet in County near Barksdale as part of the
circumference, 93 feet in height, and
American elms famous Edwards Plateau and Hill
supposedly planted in the 1880s, and and morel mushrooms Country of Texas. This is rugged terrain
recognized as a state champion tree Morel hunters in Iowa, Kansas, of small ravines and canyons with
(Snee, 2012). Missouri, and Nebraska (especially in scattered mixed juniper-oak woods.
Another site farther north at Lake
Whitney in Bosque County abundant
Fig. 2. Photo by Edward D. Forrester. Licea biforis sessile sporangia. Morchella americana fruit bodies
were collected on March 24, 2001 in
oak-juniper woods. March is the best
collecting time in South-Central to
North Texas for morel mushrooms.
Midwestern morel collection sites are
productive in early March beginning
in Texas and continuing northward
until early June in northern Minnesota.
April and May are the prime times to
collect morels in Kansas, Missouri, Iowa,
and Ohio, states where I (HWK) have
collected morels.
Collection times depend upon
adequate soil moisture with
temperatures between 50–55F and when
day and night-time temperatures vary
between 55–70F. This usually means
about the time red bud trees (Cercis
canadensis) and lilac shrubs (Syringa
American elm were most often the river bottoms of western Missouri vulgaris) start to bloom and ground
planted as a monoculture close together and surrounding bluffs of eastern plants like mayapples (Podophyllum
as they lined both street sides in Iowa Kansas) will find helpful tips for where peltatum) cover the forest floor. The
City. The mycology laboratory in the and when to locate and how to collect tree canopy is more open with sunlight
Department of Botany at University morel mushrooms in Thompson (1994). reaching ground sites because the
of Iowa was the testing center for Morels are early spring mushrooms in deciduous trees have not yet leafed out.
isolating and confirming infections of Texas and occur from early March in the Warmer earlier spring temperatures may
Ophiostoma ulmi for American elm Hill Country around Austin northward also mean earlier morel mushrooms.
in Iowa City (1967–1971). When one to the Dallas-Fort Worth area. In Texas, Old abandoned apple orchards (Malus
tree became infected with O. ulmi cedar groves of mostly mountain cedar sp.) with some dying trees are also
(then referred to as Ceratiocystis ulmi), (Juniperus ashei), and less often eastern productive sites for morels. However, the
all nearby trees also became infected red cedar (Juniperus virginiana), occur spectacular “bushels of fruiting bodies”
through root grafts, so that every tree in areas that yield productive fruiting of Morchella americana that appear
on the block had to be cut down. bodies of the “yellow morel” (Morchella in season around dying American elm
A group of dead elm trees was found americana), formerly called M. esculenta trees were the best habitats according to
near Hawkeye Drive Apartments where (see Bunyard, 2013, for discussion of Thompson (1994).
married students and our family lived name changes). An interesting report In the 1950s and 1960s American elm
on the outskirts of Iowa City. These of morels (Morchella americana) was trees were dying by the thousands of
dead trees were still standing; their described for the first time at River Dutch elm disease in cities and towns
outer layers of bark were separating Legacy Parks in Arlington, Texas, March throughout the Midwestern states and
from the wood or had already fallen 21, 1998, growing near a cedar elm this created ideal habitats for morel
to the ground (Fig. 1). Morels were (Ulmus crassifolia). A few days later mushroom hunters who flocked to their
never observed around these trees but in the same location, the giant “thick- favorite sites to find morels. However, as
24 FUNGI Volume 14:2 Spring 2021
Fig. 3. Photo by W. May. Dying Fig. 4. Photo by Walt Sturgeon, Morchella americana near dead
American elm tree. American elm tree, May 4, 2015, Columbiana County, Ohio.
Thompson notes, American elms were
most productive in the first year of dying
and even the second year after they died,
but once the bark had sloughed off, the
morels no longer were found (Fig. 3).
Thompson (1994) describes collecting
1,500 pounds a day in the 1970s.
Unfortunately, stands of American
elm today are hard to find, although
scattered trees in some areas are still
productive. Thompson’s continuous
field observations of the changing color
phases of grey to yellow Morchella
americana suggested these were color
phases of the same species that was later
confirmed by genomic studies (Fig. 4).
Fewer American elms resulted in also
locating dying cottonwood trees and
stumps as another source of morels.
Thompson was often collecting in state Fig. 5. Photo by W. May, holding boxes of morels in prime condition.
parks, and at that time it was legal, but
today in many areas it is illegal, so make
sure you follow state and federal laws.
Willie May (WM) from Missouri
has been collecting morel mushrooms
since 1991 (Fig. 5). Every spring in the
months of April and May he forays in
Missouri, Illinois, Iowa and Wisconsin,
with his first priority spotting groves of
dying elms. Healthy live American elm
trees are not usually the best source
of morel mushrooms. Indeed, if the
tree begins dying in the fall, usually
the next spring morels are not found.
Typically, American elm trees should
be completely dead before morels
Spring 2021 FUNGI Volume 14:2 25
cultures. Some field trips were made to
the American elm tree site following
rainy periods and cloudy weather of
several days but mycelium or basidiomes
were not observed. This suggests that
the discovery of fleshy macrofungi on
the trunk bark of living trees may be a
potential source of hidden biodiversity
given the use of moist chamber cultures.
Another example of macrofungi
on living healthy trees is the genus
Dendrothele referred to commonly as
white crust corticioid fungi. An on-
going study of these fungi in nature
parks, Fort Worth residential areas,
at the Botanical Research Institute of
Texas, Fort Worth Botanic Garden in
Fort Worth and in River Legacy Park,
Fig. 6. Photo by W. May. Morchella americana at base of live white ash tree. Arlington, Texas, Tarrant County, has
yielded more than 100 collections of
mostly Dendrothele jacobi on American
are induced to develop and then are fungi (and slime molds), why not try to
elms (27 trees) and cedar elms (32
limited to only a couple of years (WM, culture them indoors. Just bring in some
trees) (Bordelon et al., 2020). Cedar
personal observation). bark from live trees, set up in a moist
elms predominate on the eastern side
The two best tree species in the chamber, and watch for fruitings.
of the BRIT campus near University
Midwest associated with morel
Previous studies on tree canopy Drive (15 trees) with Dendrothele jacobi.
mushroom occurrences are American
elms, Ulmus americana, (probably the
corticolous macrofungi Healthy Juniperus virginiana (eastern
Macrofungi are known to fruit red cedar) predominate (17 trees) at
most productive and most frequent
from the bark of many kinds of trees. Tandy Hills Natural Area in Fort Worth
source of morels) and white ash,
Previously, three fleshy macrofungi with Dendrothele nivosa specifically
Fraxinus americana, (probably the
represented by Lentaria byssiseda, associated with these trees (Fig. 7).
second best tree, Fig. 6) and other
species in both genera of these trees. Mycetinis opacus, and Mycena supina
Ash trees are dying by the millions from were found on the trunk bark or lateral
emerald ash borer beetle, however, branches of living trees in the Great
dying or dead ash trees apparently do Smoky Mountains National Park
(GSMNP) (Keller, 2004; Keller et al.,
not create morel mushroom collecting
2009). More than 500 individual trees
opportunities. Unfortunately, the fate
that included 52 taxa were climbed using
of ash trees appears similar to that
the double rope climbing method and
of American elms with massive tree
sampled for myxomycetes and macrofungi
die-offs except in isolated habitats.
(Kilgore et al., 2008). This occurred each Fig. 7. Photo by Robert J. O’Kennon.
Some habitats may not have these tree
summer over an eight-year-period (2000–
species so look for alternative tree
2008). The basidiomycete macrofungi
species such as tulip tree (Liriodendron
observed and collected certainly was a Cortoicolous myxomycetes and
tulipifera); cottonwoods (Populus
scanty harvest from large healthy living American elm trees
spp.), oaks (Quercus spp.), sycamores Gilbert and Martin (1933) generally
trees in a temperate and old growth
(Platanus occidentalis), black locusts are given credit for introducing the
deciduous forest.
(Robinia pseudoacacia), black cherry Fleshy macrofungi appear to be rare moist chamber culture technique
(Prunus serotina), among others. on tree trunks and in the upper canopy using bark from living trees. Many
Although these aforementioned morel (Keller et al., 2009). In addition, the tiny myxomycete fruiting bodies were
collecting sites more frequently are the recent discovery of a novel species discovered on wetted bark samples in
sources of morels, they also may appear Mycena ulmi from an American elm glass Petri dishes taken from different
unpredictably in unexpected places tree in the Fort Worth Botanic Garden living tree species, including American
(Hemmes and Stallman, 2020). is another example of an apparent elm, referred to as “elm” in their paper.
Morel mushrooms are not the only cryptic hidden species (Perry et al., Gilbert was a student of G. W. Martin
fungi associated with elm trees. This 2020). At least six field trips failed to working in the Mycology Laboratory
spring be on the lookout for other detect any basidiomes of Mycena ulmi at the University of Iowa (Keller, 2012).
macrofungi—some fruiting directly on the trunk bark surface but moist Moist chamber bark cultures from living
from the bark of elms. And if you want chamber cultures yielded 12 collections trees yielded 30 myxomycete species;
to better your chances at seeing some all developed in tree bark moist chamber however, in some cases, the source of the
26 FUNGI Volume 14:2 Spring 2021
tree species was not given (Gilbert and
Martin, 1933). Noteworthy observations Order Echinosteliales Clastoderma debaryanum var. emperatorium+,
included the fast-forming fruiting C. microcarpum*, Echinostelium arboreum+, E.
bodies, some on the second or third day coelocephalum+, E. minutum+
after wetting and others after five or six
days. Myxomycete species cultivated Order Liceales Cribraria minutissima+, C. violacea+, Licea
from elm bark were Comatricha laxa, biforis*+, L. denudescens*+, L. inconspicua*, L.
C. fimbriata, Enerthenema papillatum, iridescens+, L. kleistobolus*+, L. marginata*, L.
Clastoderma debaryanum var. nannengae+, L. parasitica*+, L. pedicellata+, L.
emperitorium, Cribraria minutissima, perexigua+, L. scyphoides*+, L. a spiny-spored
C. violacea, Licea biforis, L. tenera, undescribed new species+; L. an orange-
Hymenobolina parasitica (currently as operculate new species+
Licea), Margarita metallica (currently
as Calomyxa), Ophiotheca wrightii Order Physarales Badhamia affinis*, Badhamiopsis ainoae*+,
(currently as Perichaena chrysosperma), Diderma chondrioderma*, D. corrugatum*,
Arcyria cinerea, and Hemitrichia Didymium clavus*+, D. orthonemata*,
minor. Echinostelium minutum is Physarum crateriforme*+, Trabrooksia
listed as common on frondose and applanata*
coniferous trees but no specific tree was
named. These species are considered Order Stemonitales Comatricha fimbriata+, C. laxa*+, Enerthenema
corticolous myxomycetes that develop, papillatum+, Macbrideola cornea+, M.
grow and form fruiting bodies on decapillata+, M. martinii+, M. scintillans+
the bark surface of living trees and
woody vines (Keller and Braun, 1969; Order Trichiales Arcyria cinerea*+, Calomyxa metallica*+,
Everhart and Keller, 2008; Keller et al., Dianema (clustered spores) +, Minakatella
2008; Keller et.al., 2009). Most of these longifila*, Perichaena chrysosperma*+, P.
corticolous myxomycetes have been depressa*+, P. minor+, 42 total species
collected in the field on bark of living
trees especially Juniperus virginiana TABLE 1. Myxomycete species list from American elm trees (taxa arranged
and Ulmus americana (Keller and alphabetically by genus and species). Corticolous myxomycete species listed from
Braun, 1999; Keller et.al, 2009); Parker multiple living American elm trees based on field collections (*) and moist chamber
and Keller, 2003). bark cultures (+) arranged by taxonomic orders and alphabetically by genus
The majority of myxomycete fruiting and species (Gilbert and Martin, 1933; Gilbert, 1934; Martin and Alexopoulos,
bodies develop along the bark edges “edge 1969; Keller and Braun, 1999; and HWK collection books). These collections were
effect” and in deeper crevices and pockets compiled over a period of about 70 years, and along with those from eastern
where these areas stay wetter longer and red cedar, represent the two species of trees where the majority of corticolous
dry out more slowly than on the bark myxomycete species occur (Keller et al., 2009).
surface. Corticolous myxomycete species
ferns, fungi, lichens, liverworts, mosses, associated with morels. American elms
diversity appears highest in rank order:
myxobacteria, and tardigrades, on the also had approximately 42 species of
eastern red cedar, American elm, and red
trunk bark of living trees and woody corticolous myxomycetes (see Table 1)
maple (Acer rubrum).
vines high in the tree canopy in GSMNP and ranked in the top four tree species.
In another paper, Gilbert (1934)
(Snell and Keller, 2003; Snell et al., 2003; Many of the smaller myxomycete species
described three corticolous myxomycete
Keller et al., 2003, Davison and Keller, in the genera Echinostelium and Licea
species new to science: Macbrideola 2004; Keller, 2004; Keller et al., 2004; are found on the trunk bark of living
scintillans and M. decapillata Keller, 2005; Keller, et al., 2009; Kilgore trees (Keller and Brooks, 1976; Keller
(Macbrideola is a commemorative et al., 2008; Keller and Barfield, 2017). and Brooks, 1977; Keller and Braun,
generic name for Thomas H. Macbride, Elm trees were not included in these tree 1999; Marshall and Keller, 2018; Keller
a world famous myxomycetologist and canopy studies because they were not and Marshall, 2019).
former President of the University of present in sufficient numbers and size.
Iowa) and Hymenobolina pedicellata Canopy corticolous myxomycete Methodology
(currently in the genus Licea). All three species diversity on living trees usually Field collections and sampling of
species form tiny plasmodia, each followed a higher pH pattern nearer
producing one tiny stalked sporangium Ulmus americana trees
7.0 to a lower pH of 4.0 and were rank
on tree trunk bark of living trees. American elm trees selected for this
ordered by number of species as follows:
study were the largest at each of the
Corticolous myxomycete species eastern red cedar 50, red maple 49, white
study sites; minimum trunk diameter
diversity on bark of living trees oak 41, tulip tree 39, white ash 31, white
of 60 cm at dbh, diameter at breast
pine 24 (Snell and Keller, 2003; Keller,
A series of papers documented the height=1.5 meters) and total height (18
2004; Keller et al., 2009). These same
occurrence of myxomycete fruiting to 30 meters). Nine American elm trees
tree species coincidentally also may be
bodies and other life forms, including were sampled at Oliver Nature Park,
Spring 2021 FUNGI Volume 14:2 27
two at the Fort Worth Botanic Garden, while remaining at room temperature a standard collecting box 4.5 x 10.5 x
and five at the Fort Worth Nature at approximately 22–25C. On day two 2 cm. Labels included species name.
Center and Refuge for a total of 16 trees. and day six after wetting and every two state, county, collection locality, habitat,
Dendrothele specimens were made on to four days thereafter for four weeks UTM coordinates, bark collection date,
giant American elm trees in residential the plates were examined under a Nikon wet date, harvest date, collector’s name
areas of Fort Worth, from area nature dissecting microscope with a MKII Fiber (legit) and accession number, person
parks, and the FWBG campus. Optic light source at magnifications of identifier (fide) were affixed to the box
A heavy bladed knife was used to pry 50x to 150x. Each dish was examined top. A Nikon Alphaphot light compound
tree bark samples avoiding any damage systematically from side to side after microscope was used to examine
to underlying tissues. Pieces of bark were the lid was removed to ensure that each slides and make measurements using
collected from all sides of the trunk at piece of bark was examined. However, a calibrated ocular reticule to identify
approximately 1.5 to 1.8 meters until removing the lid was minimized to avoid myxomycete species.
enough samples per tree were gathered to exposure due to aerial contamination, Microscope glass slides (75 mm x
half-fill a paper bag (ca 1000 cm3). Every especially by Trichoderma, a commonly 25 mm x 1 mm thick) with a frosted
bag was labeled with the identifying tree encountered green mold. end were used to make mounts
number, collection date, and site location. of myxomycete structures for
Most bark samples were collected
Location and preservation of identification. Small pins attached to
during the summer months of June, July, myxomycete fruiting bodies wooden handles were used to remove
and August and were placed in moist Moist chamber cultures of tree bark fruiting bodies from the bark. A droplet
chamber cultures within two weeks. Field often have tiny scattered sporangia of of clear lactophenol was placed in the
collections of Dendrothele were made Echinostelium and Licea species (less center of the microscope slide, sporangia
throughout the year whenever weather than 0.1 mm). Their size and scattered were added, and a square cover slip
conditions permitted. habit make it difficult to find these (22 x 22 mm and 0.16 mm thick) was
sporangia, therefore to save time, insect gradually lowered at an inclined angle
Moist chamber bark cultures pins (size 1 with nylon head stainless over the specimen to avoid creating air
Moist chamber culture preparation steel needle, 40 mm long and 0.35 in bubbles. Permanent slides were made
techniques were described in part diameter) and (silver flat-head 1-inch for future use by sealing the edge of the
previously (Keller et al., 2008; Keller and needles) were used to pin point fruiting cover slip with ZUT a resiniferous slide-
Marshall, 2019; Kilgore et al., 2009; Perry body locations. When moist chambers ringing compound. Identification labels
et al., 2020; Scarborough et al., 2009). were re-examined pins facilitate making were written in lead pencil on the frosted
Consult other articles that describe microscope slides for identifications. end of the slide covered with clear tape
inexpensive ways to prepare moist However, these pins may become to prevent future smudging. Slides were
chamber tree bark cultures (Keller et dislodged when preparing permanent wrapped with lens paper and placed in
al., 2008). This study followed a moist collections and type specimens on dried properly labeled collection boxes.
chamber culture protocol described tree bark glued in boxes. Pins also may
herein. Two moist chamber cultures per interfere with photographic techniques Photography using light and
tree were prepared using the American and must be removed when orienting scanning electron microscopes
elm trunk bark samples to document the the specimen under the microscope. An Olympus BH2 microscope with
corticolous myxomycetes present. Each The presence of myxomycete fruiting EPI Illumination and ultra-long working
sterile, plastic Petri dish (150 x 25 mm) bodies on dried tree bark were pin- distance objectives of 5X, 10X and 20X
was lined with one sterilized P8-creped pointed using a white paint permanent in combination with 10X eyepieces
filter paper fitted to cover the bottom. waterproof liquid opaque marker with was used to observe myxomycete
Bark samples were randomly selected an extra fine (0.7 mm) tip. A white dot sporangia. Photographic images were
from a paper bag and placed in the Petri was placed equidistant on either side made with a Sony A6000 and a NFK
dish bark outer-side up so that the bark of the fruiting body and close enough 2.5X relay lens at 10 mega-pixel settings.
pieces were close, but not overlapping in a straight line so that both the white Multiple image focal stacking was
or touching. Each Petri dish was labeled dots and specimen are in the field of used for both microscopic slides and
with the tree number, collection site, view simultaneously. This technique habit photographs. Each image stack
and date wetted on the lid and bottom should prove valuable in marking the varied between 10 to 75 individual
side. 30 mL of pH 7 deionized sterile location of myxomycete fruiting bodies images merged using Helicon Focus
water was added around the bark to in type collections especially when their software version 6.8.0. Image stacking
ensure thorough and even wetting. presence is obscured by look-alike life increased depth of field so that the entire
After 24 hours any excess water was forms. All observations of plasmodia and sporangium (stalk and spore case) were
decanted. Cultures were placed near fruiting bodies of date and time were in sharp focus. Images were optimized
a window exposed to indirect natural recorded in a notebook. Identifications using Adobe Photoshop CC 19.0.
light and ambient room light and were made using dichotomous keys and SEM specimens were mounted on
remained in the same spot unless they illustrations in Martin and Alexopoulos 12.5 mm stubs with conductive tape by
were being examined under a dissecting (1969). Pieces of dried bark with fruiting excising one of the sporangia including
microscope. Incubation occurred with bodies of myxomycete sporangia were a small amount of the substrate then
light and dark cycles of June to July removed and glued to the bottom of mounted on a piece of double stick
28 FUNGI Volume 14:2 Spring 2021
facility at BRIT includes a Hitachi sporangium of Macbrideola declinata
SU 3500 high resolution SEM which illustrates the structural parts when
was used to observe and photograph it was described as a species new to
specimens. Images were recorded in a science by Brooks and Keller (Eliasson
reduced contrast mode and processed et al., 1988). The ornamentation and
in Photoshop to retain highlight color of the spores, provides additional
information and extract the maximum morphological characters, sometimes
detail available. only seen with the higher magnification
1,000x under oil immersion objective of
Importance of myxomycete a light microscope or with the scanning
fruiting bodies electron microscope.
More information concerning the Moreover, one example of missing
importance of myxomycete fruiting morphological characters in myxomycete
bodies can be found in Keller and species descriptions is the presence of
Everhart (2010). This article published in an external stalk sheath (Figs. 9a and
Fig. 8. Photo by Harold W. Keller, FUNGI has been cited 2,933 times from 9b) and internal presence or absence
labels by Courtney M. Kilgore. June 2016–March 2021 as posted on the of stalk fibers. These morphological
tape which is attached to a small (1x2”) Univ. of Nebraska Digital Commons. stalk characters are helpful when
card stock. The card was inverted The morphological characters used in assigning taxa to genera such as
and the sporangia pressed to the top, monograph species descriptions and Comatricha, Lamproderma (Meriderma),
tapped, removed and the procedure keys to identify myxomycete species Macbrideola, and Stemonitis. Comatricha
repeated until the desired amount of the are associated with the fruiting bodies and Lamproderma have fibrous stalks
specimen had adhered to the stub. A (Martin and Alexopoulos, 1969). The characterized by an interlaced network of
small paint brush was used to distribute presence or absence of a peridium, mostly dark fibers as in Comatricha laxa
spores across the stub adhesive surface. capillitium, surface net, columella, when transmitted light passes through
The stub was coated with gold using calcareous structures, and stalks serve to the stalk (Fig. 9c) and when the stalk is
a Hummer VII sputtering machine to distinguish the orders, families, genera, embedded, sectioned, and stained with
a thickness of 3 nm. A new genomics and species (Fig. 8). This labeled stalked methylene blue (Fig. 9d). These fibers
Spring 2021 FUNGI Volume 14:2 29
Fig. 9a. Photo by Edward D.
Forrester. Comatricha species with
slime sheath at base.
Fig. 9c. Comatricha laxa, note Fig. 9f. Cross section of Stemonitis
internal strands of fibers. hollow stalk (center) stained with
methylene blue.
Fig. 9d. Comatricha laxa, note
upper portion of sporangium Fig. 9g. Macbrideola scintillans.
Fig. 9b. Photo by Edward D. with spores and stalk fibers
Forrester. Lamproderma sauteri stained blue.
stalked sporangium with
plasmodial slime sheath at base.
are sometimes difficult to see because
the stalk is too opaque and impossible
to discern their presence. However, if
the stalk is broken near the base the
fibers can be seen often protruding at
the break as in figure for Lamproderma
cribrarioides (Fig. 9e). Stemonitis species Fig. 10. Photo by Edward D.
have stalks that are hollow (Fig. 9f ). One Forrester. Echinostelium arboreum
note: the preferred term used here for stalked sporangium.
myxomycete fruiting bodies is stalk and
Fig. 9e. Photo by Edward D. Forrester. or forms) is about 1,100 species mainly
the preferred term for fleshy fungi is stipe.
because the figure has grown in recent
Lamproderma cribrarioides broken
Observations of selected stalk at base with protruding fibers
years. The actual number varies between
corticolous myxomycetes, 1060–1095 as some species are under
and sheath along edge. review due to their validity.
arranged alphabetically by information system of Eumycetozoa Echinostelium arboreum is a rare
genus and species (myxomycetes). The most recent data corticolous myxomycete that represents
Carlos Lado (2021) maintains a for myxomycete taxa is as follows: a new record for the state of Texas
running updated total of myxomycete the number of accepted species of (Fig. 10). Currently there are 18 valid
taxa as part of an online nomenclatural myxomycetes (not subspecies, varieties Echinostelium species recorded by Lado
30 FUNGI Volume 14:2 Spring 2021
Fig. 12. Photo by Edward
D. Forrester. Licea iridescens sessile
sporangium with iridescent
sides and apical debris.
Fig. 11. Photo by Edward D
Forrester. Undescribed species
of Licea with recessed lid and
raised margins (operculum).
(2021), however, E. arboreum is the only morphological details of this species are americana and Malus apple trees (Keller
species with a persistent shiny peridium. illustrated by Moreno et al. (2001). This & Braun, 1999). The sessile sporangia or
Although the stalked sporangia are species was found multiple times on short plasmodiocarps have a longitudinal
small (100–120 μm total height, 40–50 Ulmus americana trunk bark in moist slit that opens like a clam exposing the
μm in diameter) the combination chamber cultures at Oliver Nature Park bright yellow spore mass as in Fig. 2. The
of a shiny persistent peridium and in Mansfield, Tarrant County. fruiting bodies are often present in great
golden color facilitate locating and Licea biforis is a common species numbers which facilitates location and
identifying this species with a dissecting with a distinctive fusiform or date shape easy identification. Although the color is
microscope (Keller and Brooks, 1976). found on the trunk bark of living or variable, the orangish color shown here
SEM photographic images that show standing dead trees especially Ulmus is more typical.
Spring 2021 FUNGI Volume 14:2 31
spores (Fig. 15).
Fig. 15. Photo by This cone-shaped
Edward D. Forrester. mass develops first
Immature stage of Licea before the spores
pseudoconica sessile form. In addition,
sporangium. the spores appear
to develop first in
the apical region.
The mature spore-
filled sporangial
body proper is more
Fig. 13. Photo by spherical. These
moist chamber trunk
Edward D. Forrester. Crystals with
bark collections of
yellow bands.
Licea pseduoconica
on Ulmus americana
represent new
records for the state
of Texas.
possible to observe this species in Licea perexigua is a small sesssile to
the field with a 20X widefield hand short stalked corticolous myxomycete
Fig. 14. Photo lens. because of the larger size (total which is more difficult to identify
by Edward height 200–500 μm and 75–175 μm in because the spherical sporangium
D. Forrester. diameter). Species descriptions vary (40–110 μm in diameter) resembles
Stalked with reference to the peridium and other objects on the tree bark surface.
sporangium of dehiscence patterns. The photograph This species is a new record for the state
Licea pedicellata with crystal shown here fits the species description in of Texas.
adhering near base. Keller and Braun 1999: “… the spore case Licea undescribed new species. This
often dries and the wrinkled peridial rare taxon was found at Oliver Nature
surface gives the appearance of plates Park, Tarrant County, Texas on the trunk
Licea iridescens is a species recently and sutures.” This photograph (Fig. 14) bark surface of a living Ulmus americana
new to science that developed in moist shows a smooth peridial outer surface, tree in moist chamber cultures (Keller
chamber cultures with spectacular a furrowed stalk typical of most fresh and Marshall 2019). The genus Licea
iridescent sporangia often associated mature specimens in moist chambers, has about 75 valid species (Lado, 2021).
with crystals of unknown origin and and a crystal at the stalk base. Another This taxon has one morphological
irregular shapes (Fig. 12) (Keller and study of stalked Liceas by Wrigley de character not found in any other
Marshall, 2019). The sporangial sides Basanta and Lado (2005) has SEMs species of myxomycete: a transparent,
sparkle with bluish, pinkish, and reddish of this species but unfortunately does single, thin, colorless, peridium
colors when the peridium is highlighted not confirm everything in their species lacking ornamentation (Fig. 16). In
by an external incident directed optical description “…dehiscence into irregular addition, the black spores have a type of
light source illuminating the surface. A platelets 20–30 μm wide…” The dried ornamentation consisting of long spines
dark apical patch of debris forms first in sporangia displayed with SEM do not and a spore wall of uniform thickness not
early developmental stages. Crystal fields show this dehiscence pattern. found in any other species in the genus
on the tree trunk bark cover the bark Licea pseudoconica is a distinctive and Licea (Fig. 17). The sessile sporangia are
surface brightly shining with an optical diminutive species (70–120 μm in height difficult to detect and select because
light source (Fig. 13). These crystals and 55–90 μm in diameter) that has a of their tiny size and their association
vary in size, are irregular in shape, prominent whitish cone of gelatinous with Nostoc ball developmental stages
and are often associated with Licea debris apically giving the general (a cyanophycean alga) that can be
iridescens and apparently never have appearance of a snow-capped mountain. confused with sporangia. Light and SEM
been described before in the published It was described as a species new to photographic images clearly highlight
literature. These crystals were newly science by Keller and Brooks (1977) but these morphological characters.
discovered on numerous American also discussed from collections made in Licea undescribed new species.
elm trunk tree bark surfaces and are Florida (Keller 1973). Abundant sessile This taxon was rare with only a few
part of an ongoing study to determine sporangia often occur along bark edges. sessile sporangia which were distinct
their composition, origin, and function. This edge affect facilitates locating and because of the burnt orange color with
Collections: holotype: BRIT 478988. identifying sporangia highlighting the a recessed operculum with raised edges
Licea pedicellata has stalked black conical shape in profile. Developing early and a silvery surface. The circular lid
sporangia that occur abundantly on the immature sporangial stages clearly show actually popped off on several sporangia
trunk bark of living Ulmus americana the apical cone of debris as a transparent exposing the yellow spores underneath.
and Juniperus virginiana trees. It is mass separate from the underlying More specimens are needed before this
32 FUNGI Volume 14:2 Spring 2021Fig. 17. Photo
by Billy G.
Stone. SEM of
spiny spores
seen in
Fig. 16.
Fig. 16. Photo by Edward D. Forrester. Undescribed
Licea species with intact thin, membranous
peridium surrounding black spores.
taxon can be described as a species new the stalk is hollow. The thin peridium otherwise noted. SEMs presented in this
to science (Fig. 11). remains as a conspicuous collar at the publication were generated with support
Macbrideola cornea is common and juncture of the columella and stalk. from the George C. and Sue W. Sumner
widely distributed wherever Ulmus Molecular and Structural Laboratory
americana and Juniperus virginiana Epilogue at the Botanical Research Institute of
trees are found, especially in the latter American elms are more than Texas. Bob O’Kennon assisted with the
case, when these trees are planted in beautiful ornamental shade trees. Joyce collection of American elm bark. Vanessa
cemeteries throughout the Midwest Kilmer’s poem "Trees" (1913) reminds Marshall prepared moist chamber bark
and Southeast. This is a new record us how special a tree is in part because cultures, made permanent slides, and
for Tarrant County, Texas. The stalked a nest of robins may live there. But boxed and labeled specimens. Edward
sporangia (0.6–2.5 mm in total height American elm trees are far more than D. Forrester took LM photographs and
and 0.12–0.3 mm in diameter) are ornamental objects, they are part of assisted with measurement of sporangia.
widely scattered, usually solitary, with our human experience as well as many Billy G. Stone assisted with microscopic
branching capillitial threads arising from other hidden life forms that live there. slide photography and SEM preparation
the apex of the columella. Urban trees improve the streetscape in and photographs. Karen Nakasone
Macbrideola scintillans is a new many ways including: visual appeal and identified all of the Dendrothele
record for Tarrant County, Texas brilliant autumn golden-yellow fall leaf specimens. The author thanks the
but is apparently widely distributed colors for American elms; improve air University of Florida Graduate School for
throughout the world. It appears quality by absorbing CO2, deplete ozone, a Postdoctoral Fellowship that supported
widely scattered and usually solitary and reduce particulate matter and noise his research on myxomycete stalks. The
in moist chamber trunk bark cultures abatement; provide shade from solar author thanks W. May and B. Bunyard
appearing most frequently on Ulmus radiation lowering energy consumption for much valuable morel information and
americana and Juniperus virginiana in residential areas; serve as home and tips. This paper is dedicated to Professor
living trees in North America. A detailed shelter for wildlife including nesting Dr. Thomas W. Gaither, who was a Ph.D.
species description, LMs, SEMs, and and roosting birds, squirrels, and other student with HWK at the University
photographic illustrations highlight fauna; reduce storm water runoff and of Iowa and co-author of myxomycete
this species in Eliasson et al. (1988). protection from wind; increase property publications, outstanding botany teacher
In addition, Keller and Braun (1999) real estate values; these are some of the and field botanist, and a member of the
discuss this species with excerpts quoted value-added benefits of trees. How many famous FRIENDSHIP 9 from Rock Hill,
here: “The sporangia are 50–150 μm of you remember the tree in your yard South Carolina.
in diameter and 125–300 μm in total that you climbed during your youth or
height. The silvery, persistent peridium built a tree house or played hide and
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