"The Mouldy Marshmallow" Amaurodon caeruleocaseus (Thelephorales, Basidiomycota) - the first stipitate species in the genus Amaurodon

Abstract

Amaurodon (Thelephorales, Basidiomycota) constitutes a small but globally distributed genus in the order Thelephorales that is thought to be saprotrophic. Previously described species are soft and corticioid, with a smooth or hydnoid, blue to green hymenium which turns green after drying and have spores that turn purple in KOH. Based on sequences from the nuclear rDNA regions ITS1-5.8S-ITS2 (ITS) and 28S Amaurodon caeruleocaseus is described from Western Australia - a species that has all the morphological features common to the genus, with the interesting exception of forming a stipitate basidiome with a marshmallow-like consistency. Its closest relative is shown to be A. mustialaensis. The two species are unique within Thelephorales in having spores that appear smooth rather than ornamented under a light microscope. A key to the genus Amaurodon is also provided.

Full text

Sydowia 74 (2022) 181
DOI 10.12905/0380.sydowia74-2021-0181 Published online 22 December 2021
“The Mouldy Marshmallow”
Amaurodon caeruleocaseus
(Thelephorales, Basidiomycota) – the rst stipitate
species in the genus
Amaurodon
Sten Svantesson1,2,3,*, Katrina Syme4, James K. Douch5, Richard M. Robinson6 & Tom W. May3
1 Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, 405 30 Göteborg, Sweden
2 Gothenburg Global Biodiversity Centre, Box 461, 405 30 Göteborg, Sweden
3 Royal Botanic Gardens Victoria, Birdwood Ave, Melbourne, Victoria 3004, Australia
4 24 Offer St, Denmark, Western Australia 6333, Australia
5 Department of Veterinary Biosciences, The University of Melbourne, Parkville, Victoria 3010, Australia
6 Department of Environment and Conservation, Brain Street, Manjimup, Western Australia 6258, Australia.
*e-mail: sten.svantesson@bioenv.gu.se
Svantesson S., Syme K., Douch J.K., Robinson R.M. & May T.W. (2020) “The Mouldy Marshmallow” Amaurodon caeruleoca-
seus – the rst stipitate species in the genus Amaurodon. – Sydowia 74: 181–192.
Amaurodon (Thelephorales, Basidiomycota) constitutes a small but globally distributed genus in the order Thelephorales that
is thought to be saprotrophic. Previously described species are soft and corticioid, with a smooth or hydnoid, blue to green hyme-
nium which turns green after drying and have spores that turn purple in KOH. Based on sequences from the nuclear rDNA re-
gions ITS1-5.8S-ITS2 (ITS) and 28S Amaurodon caeruleocaseus is described from Western Australia – a species that has all the
morphological features common to the genus, with the interesting exception of forming a stipitate basidiome with a marshmal-
low-like consistency. Its closest relative is shown to be A. mustialaensis. The two species are unique within Thelephorales in hav-
ing spores that appear smooth rather than ornamented under a light microscope. A key to the genus Amaurodon is also provided.
Keywords: molecular systematics, taxonomy, stipitate, resupinate. – 1 new taxon.
The order Thelephorales Corner ex Oberw. is a
globally distributed group of basidiomycete fungi.
According to Kirk et al. (2008), it comprises 269 de-
scribed species. However, at 1.5% sequence dissimi-
larity, the sequence database UNITE (Kõljalg et al.
2005, Nilsson et al. 2018) hosts 4305 OTUs belong-
ing to the order. Following this measure Thelepho-
rales is of similar diversity to the more well-known
orders Russulales Kreisel ex P.M. Kirk, P.F. Cannon
& J.C. David (4020 OTUs) and Boletales E.-J. Gil-
bert (2106 OTUs) but the overwhelming majority of
species are yet to be formally described. The order is
rather uniform in both micromorphology and ecol-
ogy: nearly all species have warted to echinulate
spores and an ectomycorrhizal life strategy (Stalp-
ers 1993, Kõljalg 1996, He et al. 2019). The excep-
tions are the relatively small saprotrophic genera
Odontia Pers., Lenzitopsis Malençon & Bertault
and probably Amaurodon J. Schröt., the latter in-
cluding Amaurodon mustialaensis (P. Karst.) Kõl-
jalg & K.H. Larss. – the only species in the order
with spores that appear smooth under a light mi-
croscope (but nely verrucose in SEM; Ginns 1989,
Kõljalg 1996, Miettinen & Kõljalg 2007, He et al.
2019). Basidiome shape, however, varies considera-
bly; most Thelephorales are corticioid (Odontia,
Amaurodon, Tomentella Pers. ex Pat., Pseudoto-
mentella Svrcˇek, Tomentellopsis Hjortstam), but
stipitate hydnoid species are also numerous (Hyd-
nellum P. Karst., Sarcodon Quél. ex P. Karst., Phel-
lodon P. Karst.; Stalpers 1993, Kõljalg 1996, He et
al. 2019). A few nger-like (Thelephora Ehrh. ex
Willd.), stipitate smooth (Thelephora, Polyozellus
Murrill) and stipitate poroid (Boletopsis Fayod)
species also exist, as well as two lamellate species
(Lenzitopsis; Stalpers 1993, He et al. 2019).
The genus Amaurodon currently comprises ten
species (He et al. 2019). They have soft, corticioid
basidiomata, whose mature hymenia are green to
blue when fresh but turn green after drying (Kõl-
jalg 1996, Kõljalg & Ryvarden 1997, Agerer &
Bougher 2001, Miettinen & Kõljalg 2007, Gardt et
al. 2011). The hyphal system is monomitic, the hy-
phae are clamped and, with the possible exception
of Amaurodon aquicoeruleus Agerer, all parts of the
basidiomata are inamyloid. The spores are orna-

182 Sydowia 74 (2022)
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
mented (with the previously mentioned exception
of A. mustialaensis), hyaline to pale yellow or blue
in water but turn purple in KOH. The genus is glob-
ally distributed and thought to be saprotrophic
(Kõljalg 1996, Kõljalg & Ryvarden 1997, Agerer &
Bougher 2001, Miettinen & Kõljalg 2007, Gardt et
al. 2011).
The purpose of this article is to place phyloge-
netically and describe a new species of Thelepho-
rales from Western Australia with the unique char-
acter combination of stipitate basidiomata and
smooth spores. The species has been colloquially
referred to as the “mouldy marshmallow” by its
original nder (KS), with reference to its strange,
soft consistency when fresh and blue-green, warted
hymenium.
Materials and methods
Morphological data
Specimens were studied macroscopically and at
20× magnication under a dissecting microscope.
Micromorphological measurements were made at
630× magnication in the software Olympus cellS-
ens Standard 1.16, using an Olympus BX51 micro-
scope equipped with an Olympus DP73 camera. The
microscope samples were prepared from dried ma-
terial, mounted in 5 % KOH, in Melzer’s reagent
and in water. A few samples prepared for imaging
were also made in a solution of Congo Red and in-
undated with KOH. Measurements were made on
20–30 structures of each type to the nearest 0.5 µm,
except for basidia, whose length was measured to
the nearest µm. Spore measurements exclude the
hilar appendage. Measurements of basidial width
were made at the widest part of the basidia; basidi-
al length excludes sterigmata. The width of hyphae
was measured on unbroken, internodal sections.
Measurement statistics follow Svantesson et al.
(2019). Herbarium codes follow Index Herbariorum
(Thiers 2020).
Molecular data
Genomic DNA was isolated from PERTH
06670709 using EZNA Forensic DNA kit (OMEGA).
Fungal tissues were crushed in lysis solution with
micropestles and incubated for at least one hour at
65 °C. The procedure then followed the standard
protocol for isolating DNA “from hair, nails and
feathers”, except that the nal elution was done in
50 µl of elution buffer. The primer set ITS1-F
(Gardes and Bruns 1993) and ITS4 (White et al.
1990) was used to amplify the 5.8S gene and the two
ITS regions of the nuclear rDNA (ITS). Each PCR
mixture contained 1X PCR buffer, 25 µg BSA (Sig-
ma–Aldrich Co.), 1.5 mM MgCl2, 0.2 µM dNTPs (In-
vitrogen), 0.5 µM of each primer, one unit of Hot-
StarTaq DNA polymerase (QIAGEN, Rockville,
MD), 1-3 µl of genomic DNA and sterile distilled
water to a total of 25 µl. The thermal cycling condi-
tions were: initial denaturation at 95 °C for 15 min,
followed by 35 cycles of 94 °C for 20 s, 52–58 °C for
45 s according to the primer sets used, and 72 °C for
1 min and a nal elongation step consisting of 72 °C
for 5 min. Sequences were edited, cleaned and as-
sembled in Geneious Pro v.8.1.7 (Biomatters Ltd.).
Also relevant to this study is the ITS sequence
KP311452 from collection MEL 2231735 that was
lodged as part of a barcoding program for Austral-
ian fungi in 2014 (Tab. 1). The collection was origi-
nally identied as Hydnellum sp., but the sequence
was recovered as a high BLAST match to the newly
generated sequence (and there is a 28S sequence
from the same collection). Sequencing of other ge-
netic regions was not attempted, since a multi-gene
reference dataset for other Amaurodon species is
currently lacking. Genbank numbers of sequences
generated for this study are provided in the species
description.
The DNA dataset (Tab. 1) was assembled from
the available sequences of the new species and one
sequence per species from the following: all previ-
ously described Amaurodon species with sequences
available on UNITE or Genbank, two species from
all other Thelephorales genera and an outgroup
consisting of Corticium roseum and Waitea circi-
nata. Within Amaurodon, when a species name was
attributed to sequences that belonged to more than
one non-singleton 1.5% UNITE Species Hypothesis
(SH) that all included basidiome sequences, then
one representative sequence per SH was included in
the dataset. In addition, one representative from
each 1.5 % Amaurodon SH that included Australi-
an sequences, basidiome-sourced or otherwise, were
added to the dataset, unless they were already pre-
viously represented. No ITS sequence was available
for Amaurodon angulisporus Gardt & Yorou, and
for the outgroup taxa ITS proved hard to align; for
these three taxa the dataset was therefore limited to
28S sequences. Genbank and UNITE were queried
for additional sequences of the new species.
Alignment of concatenated ITS and 28S se-
quences was made in AliView 1.18 (Larsson 2014),
utilizing the L-INS-i strategy as implemented in
MAFFT 7.017 (Katoh & Standley 2013), followed by
manual trimming of the ends of sequences. The re-
sulting alignment was 1870 bases long.

Sydowia 74 (2022) 183
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
Tab. 1. Analysed sequences and their vouchers. * holotype of A. caeruleocaseus. New sequence generated in this study in bold.
Species
Voucher (herbarium,
strain or collector’s
no.)
Geographic
origin
INSDC/UNITE accession no.
Reference
ITS 28S
Amaurodon aeruginascens TU115236 Venezuela UDB018562 UDB018562 Nilsson et al. 2018: UNITE
Amaurodon angulisporus SYN2217 Burkina Faso – FR823360 Gardt et al. 2011
Amaurodon aquicoeruleus TU100989 Australia AM490944 AM490944 Miettinen & Kõljalg 2007
Amaurodon atrocyaneus TU115234 Ethiopia UDB018567 UK155lsu UNITE
Amaurodon caeruleocaseus
PERTH06670709 Australia MT565478 – This study
Amaurodon caeruleocaseus MEL2231735* Australia KP311335 KP311452 Bonito & May unpubl.
Amaurodon hydnoides TU108407 Venezuela AM490941 AM490941 Miettinen & Kõljalg 2007
Amaurodon mustialaensis TU100621 Estonia UDB011100 UDB011100 UNITE
Amaurodon sp. GL11377-103-S063 Australia KY687668 KY687668 Tedersoo et al. 2017
Amaurodon sumatranus TU115407 Malaysia UDB016291 UDB018730 UNITE
Amaurodon viridis TAAM149664 Russia USB000294 UDB018710 UNITE
Amaurodon viridis TU123021 UK UDB032772 UK908 UNITE
Boletopsis grisea TU108150 Estonia UDB000293 UK36_LSU UNITE
Boletopsis leucomelaena Krikorev140912 Sweden MK602710 MK602710 Larsson et al. 2019
Corticium roseum CBS205.91 Canada – EF537893 Genbank
Hydnellum geogenium E. Bendiksen526-11 Norway MK602725 MK602725 Larsson et al. 2019
Hydnellum suaveolens S. Svantesson 877 Norway MK602736 MK602736 Larsson et al. 2019
Lenzitopsis daii Yuan2952 China JN169798 JN169794 Zhou & Kõljalg 2013
Lenzitopsis oxycedri K.H. Larsson15304 Spain MK602774 MK602774 Larsson et al. 2019
Odontia ferruginea TAAM149492 Estonia UDB000285 UDB018691 UNITE
Odontia brosa TU115028 China UDB018450 UDB018450 UNITE
Phellodon niger E. Larsson35-14 Sweden MK602782 MK602782 Larsson et al. 2019
Phellodon tomentosus E. Bendiksen11-180 Norway MK602781 MK602781 Larsson et al. 2019
Pseudotomentella avovirens T1123 Norway MK290726 MK290726 Svantesson et al. 2019
Pseudotomentella mucidula K.H. Larsson16310 Sweden MK290723 MK290723 Svantesson et al. 2019
Sarcodon imbricatus TU108129 Estonia USB016767 UDB016767 UNITE
Sarcodon squamosus TU100663 Estonia UDB003290 UK687_LSU UNITE
Thelephora terrestris TAAM162083 Estonia AF272923 UDB018696 Kõljalg et al. 2000, UNITE
Thelephora palmata TU115271 Sweden UDB018570 UDB018570 UNITE
Tomentella ferruginea TAAM166877 Estonia AF272909 UDB018702 Kõljalg et al. 2000, UNITE
Tomentella pisoniae TU103671 Seychelles FM244908 FM244908 Suvi et al. 2010
Tomentellopsis echinospora TAAM180763 Estonia UDB018591 UDB019408 UNITE
Tomentellopsis zygodesmoides JS27216 Norway AJ410759 UDB018729 Kõljalg et al. 2002, UNITE
Waitea circinata CBS315.84 Netherlands – AY885164 Genbank

184 Sydowia 74 (2022)
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
Molecular analyses
Gblocks 0.91b (Castresana 2000, Talavera &
Castresana 2007), was used to trim the alignment of
problematic character regions (e.g. saturated sites
and sections with unclear homology). The program
was run in its relaxed version, as outlined by Tala-
vera & Castresana (2007), which according to the
same has been evaluated as suitable for alignments
created by MAFFT and intended for Maximum
Likelihood (ML) analysis. Gblocks has seemingly
not been evaluated for Bayesian inference (BI)
methods, which together with ML analysis was em-
ployed in this study for estimating gene trees, but
for neighbour joining, parsimony and maximum
likelihood. Although they are reached in very dif-
ferent ways the results of ML and BI tend to be the
most similar, and the alignments output for the ML
analysis was hence also used in the BI analysis.
RDP4 (Martin et al. 2015) was used to test for
recombination. During a rst round of testing the
methods RDP, GENECONV, Chimaera and MaxChi
were used and the signicance level set to 0.01. Se-
quences with signicant signs of recombination
were subjected to a second round of testing that
made use of all recombination methods. Any se-
quences with a positive result for more than two
methods with p-values ≤ 10-5 in the second round
were regarded as probable recombinants.
To generate BI phylograms BEAST 2.6.2 (Bouc-
kaert et al. 2014, 2019) was used. The xml-les
were prepared in the associated software BEAUti
2.6.2 (Bouckaert et al. 2014, 2019). The automated
best-t test implemented in PAUP* 4.0a (Swofford
2002) was used to select optimal substitution mod-
els and optimal substitution model partitions for
the following minimal partitions: ITS1, ITS2, 5.8S
and 28S. Models with three substitution schemes
and equal or gamma-distributed among-site rate
variation and partitions based on such models
were evaluated based on BIC score. The partitions
ITS1+ITS2 and 5.8S+28S, both with SYM+G as
substitution model provided the best t. In BEAST,
the SYM+G model is not available, and therefore
the model implemented was GTR+G for both par-
titions, as it is the most similar model to SYM+G
available in the program. The trees of the minimal
partitions were set as linked and the clock models
as unlinked. A lognormal, relaxed clock model was
assumed for each, since test runs had shown that
all partitions had a coefcient of variation well
above 0.1 (i.e. implying a relatively high rate vari-
ation among branches). The clock rate of each par-
tition was estimated in the run, using a lognormal
prior with a mean set to 1 in real space. The growth
rate prior was set to lognormal, with a mean of 5
and a standard deviation of 2. The Markov Chain
Monte Carlo (MCMC) chain was run for 50 million
generations, with tree and parameter les sampled
every 5000 generations. The analysis converged
well in advance of the 10 % burn-in threshold, had
an ESS value well above 200 for all parameters,
and satisfactory chain mixing, as assessed in Trac-
er 1.6.0 (Rambaut et al. 2014). After discarding the
burn-in trees, a maximum clade credibility tree
was identied by TreeAnnotator 2.6.2 (Bouckaert
et al. 2014, 2019).
A ML phylogram was generated in W-IQ-TREE
(Nguyen et al. 2015, Trinopoulos et al. 2016). The
program was run with the standard settings of im-
plementing a substitution model chosen by the as-
sociated ModelFinder software (Kalyaanamoorthy
et al. 2017) and 1000 Ultrafast Bootstrap and SH-
aLRT branch test replicates, respectively. The best
t model chosen by ModelFinder was TIM3e+I+G4.
Clades with UFBoot support values ≥ 95 and SH-
aLRT support values ≥ 80 % are regarded as reliable
(Guindon et al. 2010, Minh et al. 2013).
The resulting trees from the BI and ML analyses
were visually prepared in FigTree 1.4.3 (Rambaut
2012), Dendroscope 3.7.2 (Huson & Scornavacca
2012) and Inkscape 0.92.3. (https://inkscape.org).
Results
The phylogenetic analyses of all ITS and 28S se-
quences of Amaurodon available in GenBank and
UNITE support the genus as monophyletic (Fig. 1).
Within Amaurodon, the two sequences of the new
species, A. caeruleocaseus are supported as a sister
taxon to A. mustialaensis. These two sequences are
identical and no similar sequences were retrieved
upon query of either Genbank or UNITE. No se-
quences were found to be recombinants.
When UNITE was searched for undescribed
Amaurodon sequences from Australia belonging to
a 1.5 % SH not tied to a described species, only one
match was returned, SH1506916.08FU which con-
sists of KY687668 from a soil sample from the Aus-
tralian state of Victoria (Tedersoo et al. 2017). It is
phylogenetically distant from A. caeruleocaseus
and A. aquicoeruleus, and is instead a potentially
undescribed sister species of Amaurodon atrocya-
neus (Wakef.) Kõljalg & K.H. Larss. – a species orig-
inally described from Venezuela.
Sequences from specimens identied as Amau-
rodon viridis (Alb. & Schwein.) J. Schröt. were
found to belong to two different 1.5 % UNITE SHs

Sydowia 74 (2022) 185
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
which are strongly supported as sister taxa in both
the BI and ML analyses.
Taxonomy
Amaurodon caeruleocaseus
Svantesson & T.W. May,
sp. nov. – Fig. 2
MycoBank no: MB 835801
D i a g n o s i s . – Distinguished from all other
Amaurodon species by its stipitate basidiomata and
its spores, which are almond-shaped and appear
smooth under a light microscope.
Etymology. – caeruleocaseus (Latin) is a
noun in apposition derived from caeruleus = blue
and caseus = cheese, which refers to the macroscop-
ic similarity of the basidiomata to blue cheese in
colour and texture.
Ty p i f i c a t i o n . – AUSTRALIA. WESTERN
AUSTRALIA: Darling, Denmark, Loc 3298 off Rail-
way Reserve Road W of Mt McLeod Road, under
sword sedge (Lepidosperma sp.), at the base of kar-
ri (Eucalyptus diversicolor), 1 Jul 2003, K. Syme
1280/03 (holotype MEL 2231735!; isotype: PERTH).
GenBank: ITS = KP311452.
UNITE SH: SH1241369.08FU
Description. – Basidiomata annual,
stipitate, vaguely and irregularly inversely cone-
shaped to funnel-shaped, often conuent; 1–9 cm
tall and 1–4 cm wide. P i l e u s usually ± circular,
irregular, sometimes spathulate, with attened
Fig. 1. Maximum Likelihood phylogram of Thelephorales with in-depth sampling of Amaurodon, based on ITS+28S alignment;
posterior probability values added from concordant BI tree. Nodes/branches with SH-aLRT bootstrap ≥ 80, Ultrafast bootstrap
≥ 95 and posterior probability ≥ 95 are thickened; full support by all methods is indicated by an asterisk. Where the lower thresh-
olds of all methods are not met, SH-aLRT is displayed above branches and posterior probability below. Branch lengths are scaled
in substitutions/site. Identiers are Genbank/UNITE ITS accession numbers; when ITS is lacking: 28S accession numbers.

186 Sydowia 74 (2022)
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
Fig. 2. Macro- and micromorphological features of A. caeruleocaseus (A–B: MEL 2231735, holotype; C: PERTH 06670709). A. Spores
in Congo Red inundated with KOH (bar = 10 µm). B. Clamp on context hypha (bar = 10 µm). C. Basidiomata (bar = 1 cm).

Sydowia 74 (2022) 187
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
lobes or protrusions; surface radially brillose, dry,
felt-like to nely velvet-like; often tufted and pitted
at the centre; pale yellow to brownish yellow at the
centre, pale greyish blue to violet at the edges; white
to pale greyish green after drying. Underside with
distinct contrast between sterile zone distal to stipe
and the hymenium. S t e r i l e z o n e at to shal-
lowly, radially folded; surface texture same as pile-
us; white to pale brownish yellow or pale blue green,
concolourous with upper side after drying. H y m e -
n i u m often irregularly decurrent on stipe; formed
over and between evenly rounded to attened warts
or irregular tubercles, measuring up to 1 mm in
height, often shorter; green to blueish green or grey-
ish blue when fresh, green after drying. S t i p e
centrally or near centrally attached, sometimes
branched; 0.2–2 cm in diameter, tapering down-
wards, sometimes with a root-like basis; round or
attened in cross-section, sometimes twisted; sur-
face dry, very nely felt-like; pale brownish yellow
to almost white or very pale blueish green, bruising
blue to blueish green, with time almost black; con-
colourous with pileus after drying. C o n t e x t when
fresh very pale pinkish yellow, easily compressed
yet hard to tear – somewhere between marshmallow
and suede in texture; after drying concolourous
with pileus and brittle. S m e l l not documented
when fresh; insignicant when dried. T a s t e not
documented when fresh; faintly bitter, mildly un-
pleasant when dried.
H y p h a l s y s t e m monomitic, clamp connec-
tions present on all hyphae. Tr a m a l h y p h a e in-
terwoven in direction of tissue growth; forming a
rather loose tissue. Individual hyphae (3.0)3.5–
5.0(5.5) µm wide (mean width 4.2 µm), thin-walled;
clamps conspicuous, often looped (i.e. with a gap
between clamp and hyphae); sparsely encrusted
with rod-shaped to granular, hyaline crystals. In pi-
leus with a quickly passing yellowish green reaction
in KOH (visible macroscopically when the cover
glass is applied, but often gone once placed under
the microscope), then hyaline; in water hyaline,
with strongly granulated contents; inamyloid. In
stipe with longer-lasting yellowish green reaction
in KOH, eventually pale blackish purple; same as
cap hyphae in water; very rarely amyloid. P i l e u s
s u r f a c e h y p h a e pointing outward, sometimes
sinuous, sometimes with weak blackish purple re-
action in KOH, otherwise same reactions as tramal
cap hyphae. Stipe surface hyphae same as
tramal stipe hyphae. S u b h y m e n i a l h y p h a e
thin-walled; forming a rather loose tissue; with the
same width as tramal hyphae; hyaline in KOH and
water; with strongly granulated contents in water;
inamyloid to amyloid. B a s i d i a with four straight
to almost straight sterigmata; narrowly clavate to
clavate, sometimes clavopedunculate; thin-walled;
often with one–three slight constrictions. Dimen-
sions: (35)36–43(47) × (4.5)5–(7.5) µm; mean dimen-
sions: 40 × 6.0 µm. Sterigmata (2.5)3.0–3.5 µm long,
with a mean length of 3.2 µm. Hyaline in KOH and
water; with strongly granulated contents in water;
weakly to strongly amyloid. C y s t i d i a l o r g a n s
lacking. B a s i d i o s p o r e s narrowly ovoid to
ovoid in frontal view, almond-shaped in lateral
view; smooth; conspicuously thick-walled. Dimen-
sions in lateral view: 5.5–6.5 × 4.0–4.5 µm; mean di-
mensions: 6.0 × 4.5 µm; Q-value: 1.30–1.47; mean
Q-value: 1.38. Colour in KOH yellow to brownish
yellow, in the presence of air staining purple to
nearly black; in water very pale brownish yellow to
very pale green or nearly hyaline; strongly amyloid.
Chlamydospores lacking.
D i s t r i b u t i o n . – Only known from ve local-
ities, within 160 km of each other, in the south-west
of Western Australia.
H a b i t a t . – Two of the ve localities, Mount
Shadforth Nature Reserve and Walpole-Nornalup
National Park are covered by old-growth Eucalyp-
tus diversicolor F. Muell. forests (Corymbia calo-
phylla (Lindl.) K.D. Hill & L.A.S. Johnson and E.
brevistylis Brooker also present). The third locality,
Harewood Forest, is also dominated by E. diversi-
color, but in this case the forest was at least par-
tially logged long ago. The fourth locality, Denmark,
is a partly-cleared E. diversicolor forest, bordering
very old pasture on a long abandoned farm. These
four localities have not burned since 1937. The fth
locality, Carter Forest Block, was a Eucalyptus mar-
ginata Donn ex Sm. and C. calophylla regrowth for-
est following at least partial logging in the 1940s,
but had been gap release harvested and regenera-
tion burnt nine years prior to collection.
Conservation status. – Amaurodon caer-
uleocaseus appears to be a rare species with a very
limited distribution. The nders of the specimens,
KS and RR have continuously surveyed vast areas
of forest, but have only encountered the species ve
times since they became aware of its existence (in
the case of KS since 1983). More data on the distri-
bution, ecology, response to disturbance and occur-
rence frequency of A. caeruleocaseus is needed to
determine its conservation status and inform po-
tential Red Listing and protection. Therefore, fur-
ther search for and reporting of the species is
strongly encouraged, which will be aided by its
unique appearance. In particular, it would be help-

188 Sydowia 74 (2022)
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
ful to investigate the possibility of hyphal connec-
tions between basidiomata and ectomycorrhizal
root tips.
R e m a r k s . – The almond-shaped spores and,
more strikingly so, the stipitate basidiomata of A.
caeruleocaseus makes it morphologically unique
within the genus Amaurodon. The amyloid reaction,
observed to a varying degree in its basidia, subhy-
menial hyphae and strongly in its spores, is another
morphological feature that has not been earlier re-
corded for the genus, possibly with the exception of
the spores of A. aquicoeruleus. However, since the
authors of A. aquicoeruleus described its spores as
“dark blue” rather than purple in Melzer’s reagent
and also noted them to be bright blue in water, it
seems likely that their description referred to the
spores’ inherent colour rather than an amyloid reac-
tion of the same (Agerer & Bougher 2001). The soft
basidiome, the verrucose-tuberculate hymenial sur-
face, which is blue to green when fresh and green
after drying, and the purple reaction of the spores
in KOH are otherwise typical morphological fea-
tures of the genus.
The species most similar to A. caeruleocaseus in
micromorphology is A. mustialaensis, which also
has spores that appear smooth in light microscopy
and clamped hyphae (Kõljalg 1996). This is, howev-
er, a species with smooth, corticioid basidiomata
and ellipsoid spores, so far only documented from
the Northern hemisphere (Kõljalg 1996, Kõljalg et
al. 2005, Nilsson et al. 2018). Two species of Amau-
rodon have been reported so far from Australia: A.
viridis (records summarised in May et al. 2003) and
A. aquicoeruleus (Agerer & Bougher 2001). Both are
very different from A. caeruleocaseus, since they are
corticioid and have ornamented spores.
Amaurodon viridis is a species described from
Europe. Australian specimens placed under that
name probably represent another species. Two
names based on Australian types (both from Tasma-
nia) currently synonymized with A. viridis exist.
Thelephora viridis Berk. (a later homonym of Thel-
ephora viridis Preuss) and Hypochnus chlorinus
Massee were synonymized by Cunningham (1963),
who incorrectly adopted the name Tomentella vir-
idis “(Berkeley) G. H. Cunningham”, which should
be cited as T. viridis (Rick) G.H. Cunn. based on the
replacement name for T. viridis which is Kneifa
viridis Rick. If conspecic, the correct name for the
taxon including the types of T. viridis and H. chlori-
nus should be based on the latter as it has date pri-
ority over K. viridis. Re-examination of the types of
T. viridis and H. chlorinus, preferably with sequenc-
ing (or linking to a sequenced epitype) is desirable
to clarify the correct naming of resupinate species
of Amaurodon in Australia.
Other specimens examined. – AUSTRALIA.
WESTERN AUSTRALIA: Carter Forest Block, near Donnelly,
adjacent unnamed logging track, approx. 1 km north along
Swamp Rd from Donnelly Road intersection, in recently gap
release harvested, prescribed burned forest of E. marginata
and C. calophylla, 29 May 2008, K. Syme, J. Fielder, R.M. Rob-
inson FC1248 (PERTH 06670709). GenBank: ITS = MT565478.
A d d i t i o n a l l o c a l i t i e s (observations, specimens
not collected). – AUSTRALIA. WESTERN AUSTRALIA: Den-
mark, Scotsdale Road, Harewood Forest walk trail, E. diversi-
color forest, logged long ago, S 34° 55’ 35”, E 117° 17’ 30”, 09
June 2020, K. Syme; Ibidem, Walpole-Nornalup National Park,
under tall, old-growth forest of E. diversicolor and E. brevisty-
lis, 2018, K. Syme; Ibidem, Mount Shadforth Nature Reserve,
under old-growth forest of E. diversicolor and C. calophylla
23 May 1983, K. Syme (watercolor sketch in possession of art-
ist).
Key to the species of
Amaurodon
Some names of Amaurodon species (e.g. A. vir-
idis) are today used in a very wide morphological
and geographical sense. It is doubtful whether this
corresponds to the reality of species boundaries and
it is likely that a considerable number of species are
yet to be described. For that reason, this key is as far
as possible based on original descriptions (o) or
type studies (t). Brief descriptions have been added
under each species to aid in the identication of ab-
errant specimens, potentially belonging to unde-
scribed species. Only the country of description is
noted.
1. Basidiome resupinate ........................................ 2
1.* Basidiome stipitate;
spores almond-shaped in lateral view, 5.5–6.5 ×
4.0–4.5 µm, smooth, thick-walled, nearly hyaline
to very pale brownish yellow or very pale green
in water, amyloid; cystidia absent; all hyphae
with clamps; Australia ........... A. caeruleocaseus
2. Basidiome hydnoid or smooth........................... 3
2.* Basidiome poroid;
spores subglobose to ellipsoid, 6.0–7.0 × 4.5–
5.5 µm, with low warts, thick-walled, hyaline to
brown in water, amyloid; cystidia absent; all hy-
phae without clamps; Colombia (o: Hjortstam &
Ryvarden 1988) ....................... A. aeruginascens
3. Basidiome at least in parts hydnoid ................ 4
3.* Basidiome without hydnoid parts; hymenium
smooth to very nely granular ......................... 6
4. Spores broadly ellipsoid to broadly bean-shaped
– in frontal view convex to concave ................. 5
4.* Spores subglobose – in frontal view always con-
vex;
4.3–5.6 × 3.9–4.9 µm, with very low warts,
wall-thickness not recorded, hyaline to yellow-

Sydowia 74 (2022) 189
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
ish in water, amyloidity not recorded; cystidia
absent; all hyphae with clamps; United States
(t: Miettinen & Kõljalg 2007) ............. A. viridis
5. Aculei dense, regular, cylindrical, slender,
ca 2 mm long; large, rhomboidal crystals pre-
sent in Cotton Blue;
spores broadly ellipsoid to broadly bean-shaped,
4.5–5.7 × 3.5–4.5 µm, with very low warts, slight-
ly thick-walled, yellowish brown in water, amy-
loidity not recorded; cystidia absent; all hyphae
with clamps; Venezuela (o: Kõljalg & Ryvarden
1997, t: Miettinen & Kõljalg 2007)
... A. hydnoides
5.* Aculei sparse, commonly somewhat spathulate,
ca 1 mm long; large, rhomboidal crystals absent
in Cotton Blue;
spores broadly ellipsoid to broadly bean-shaped,
4.7–5.7 × 3.7–4.7 µm, with very low warts, slight-
ly thick-walled, greyish to brownish in water,
amyloidity not recorded; cystidia absent; all hy-
phae with clamps; Indonesia (o: Miettinen &
Kõljalg 2007) .............................. A. sumatranus
6. Spores with angular bulges or low to high
warts ................................................................... 7
6.* Spores smooth in light microscope, outline even;
in frontal and lateral view ellipsoid, 4.5–7.0 ×
3.5–5 µm, thick-walled, hyaline in water, amy-
loid; cystidia absent; all hyphae with clamps;
Finland (Kõljalg 1996, Hansen & Knudsen
1997) .......................................... A. mustialaensis
7. All hyphae with clamps .................................... 8
7.* All hyphae without clamps or with very occa-
sional clamps, at least on subicular hyphae ... 9
8. Spores in frontal view globose, in lateral view
subglobose, unlobed;
spores in frontal view 4.5–5.5 µm diam., lateral
side 4.5–5.5 × 4.0–5.0 µm, with very low warts,
wall-thickness not recorded, bright to pale blue
in water, probably amyloid (dark blue in Mel-
zer’s reagent); cystidia absent; Australia (o:
Agerer & Bougher 2001) ......... A. aquicoeruleus
8.* Spores in frontal view irregularly ovoid to ellip-
soid, in lateral view ellipsoid to commonly boat-
shaped, both with obtuse angular bulges;
spores in frontal view 4.5–6.5 × 4.5–6.0 µm, in
lateral view 4.5–6.0 × 4.5–6.0 µm, lacking orna-
mentation, thin-walled, pale blue in water, in-
amyloid; cystidia-like, projecting elements
present in hymenium, some acuminate, others
hyphoid; Burkina Faso (o: Gardt et al. 2011) ......
.................................................... A. angulisporus
9. Spores ellipsoid with one side sometimes de-
pressed and up to 8.0 µm long or subglobose to
ovoid and up to 5.5 µm long; all hyphae without
clamps .............................................................. 10
9.*
Spores globose to subglobose, ca 7.0–9.0 × 7.0 μm;
clamps very occasional on subicular hyphae;
spores with blunt warts or nodules, sometimes
in pairs, up to 2 µm long, wall-thickness, colour
in water and amyloidity not recorded; cystidia
possibly present in hymenium, clavate, up to 15
µm wide; Venezuela (o: Wakeeld 1966) ..............
..................................................... A. atrocyaneus
10. Spores ellipsoid with one side depressed, 5.0–
8.0 × 3.0–4.0 µm;
with very low and sparse warts, wall-thickness
of spores, colour in water and amyloidity not re-
corded; cystidia not recorded; United Kingdom
(o: Wakeeld 1917) ........................... A. cyaneus
10.* Spores subglobose to ovoid, outline even, 5.0–
5.5 × 3.5–5.0 µm;
with broad, low warts, thick-walled, hyaline in
water, inamyloid; cystidia absent; United States
(o: Burdsall & Larsen 1974) ..... A. wakeeldiae
Discussion
Among homobasidiomycetes, lineages with stip-
itate basidiomata have been shown to have evolved
from lineages with corticioid basidiomata, with
subsequent, occasional reversions (Hibbett & Bind-
er 2002, Larsson et al. 2004). Although the phylog-
eny of Thelephorales is poorly known, the basal
clades have been indicated to comprise Tomentella+
Thelephora (probably neither is monophyletic),
Pseudotomentella, Tomentellopsis and Amaurodon
(Larsson et al. 2004). These genera all form resupi-
nate basidiomata or, in the case of Thelephora,
structurally very simple stipitate basidiomata
(Larsson et al. 2004). The discovery of A. caerule-
ocaseus hence provides yet another example of a
stipitate species arising from presumed corticioid
ancestors. It also testies to the considerable phe-
notypic plasticity of basidiome shape in homoba-
sidiomycete evolution, where species or lineages of
quite dissimilar morphology often occur within
larger lineages of a certain morphology. This is, for
example, manifested by numerous lineages of truf-
e-like fungi within genera that are otherwise stip-
itate-pileate in the Agaricales Underw., Boletales
and Russulales (Sheedy et al. 2016).
The presence of heavy ornamentation on spores
is thought to aid in insect-dispersal (Deacon 2013),
and for the resupinate genus Tomentella this modus
of spore-distribution has been conrmed (Lilleskov
& Bruns 2005). Insect-dispersal could be of assis-
tance in Tomentella, and similar genera such as
Amaurodon, whose basidiomata often occur very
low to the ground, where wind-dispersal is presum-

190 Sydowia 74 (2022)
Svantesson et al.: Amaurodon caeruleocaseus, sp. no v.
ably less effective. However, the relationship be-
tween spore ornamentation and basidiome shape in
Thelephorales is not simple. Within the order, in ad-
dition to Thelephora, almost all species in the Bole-
topsis, Hydnellum/Sarcodon and Phellodon clades
are stipitate and all species of these genera have re-
tained the feature of ornamented spores. The effect
of loss of spore ornamentation on spore dispersal is
unknown, but the concurrence of a switch in ba-
sidiome shape and loss of spore ornamentation, as
seen in A. caeruleocaseus, is intriguing, and the dif-
ferent combinations of basidiome morphology and
spore ornamentation now known in Amaurodon of-
fer interesting comparisons on which to base inves-
tigations of spore dispersal vectors. Within Amau-
rodon, there are now species with resupinate basid-
iomata and ornamented spores (most species), resu-
pinate basidiomata and smooth spores (A. mustial-
aensis) and now A. caeruleocaseus, with stipitate
basidiomata and smooth spores. Whether the spores
of A. caeruleocaseus are truly smooth or will be re-
vealed to be nely verrucose in SEM, as in A. musti-
alaensis (Ginns 1989), would be interesting to know
in this context but remains to be studied.
The genetic difference between A. caeruleoca-
seus and A. mustialaensis, as indicated by ITS and
28S sequences, is small, and the arrangement of tis-
sue in the basidiomata of the former is very simple
and unspecialized. Apart from some of the hyphae
on the upper surface of the pileus being sinuous,
there is no development of specialized tissue or hy-
phae outside the hymenium. The tufty, irregular
surface of the cap is for example nearly identical in
microstructure to the interior of the stipe. Indeed, it
would seem that the only structural invention of
this fungus is the thickening and rising of what
would have been the subiculum of its resupinate
ancestor up into the loose fountain-shaped bundle
of hyphae that now forms its erect basidiomata. The
change of basidiome shape observed in A. caerule-
ocaseus thus appears to be relatively recent and in-
volve very limited tissue differentiation from its
corticioid ancestor, suggesting that this species and
its close relatives would likely constitute good can-
didates for genomic studies of genes linked to
changes in basidiome shape.
Acknowledgements
This study was supported by a grant from Artda-
tabanken (2014-152 4.3). Erik Ljungstrand (Botani-
ska Analysgruppen) is sincerely thanked for his ad-
vice in constructing a scientic name for the species
described, Karl-Henrik Larsson (University of
Oslo) for providing feedback on the manuscript,
Gregory Bonito (Michigan State University) and
Franck Stefani (MycoDiagnostic) for generating se-
quences and Gareth Holmes (Royal Botanic Gar-
dens Victoria) for processing the same.
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(Manuscript accepted 27 October 2021; Corresponding Editor:
I. Krisai-Greilhuber)