Halimium as an ectomycorrhizal symbiont: new records and an appreciation of known fungal diversity

Abstract

Halimium is a genus of Cistaceae, containing a small group of shrub species found in open vegetation types and in degraded forest patches throughout the western and central Mediterranean region. We recently described the morpho-anatomical features of the ectomycorrhizae formed by Scleroderma meridionale on Halimium halimifolium, but the mycorrhizal biology of this host plant genus is still largely unexplored. Here, we report new data on the ectomycorrhizal fungal symbionts of Halimium, based on the collection of sporocarps and ectomycorrhizal root tips in pure stands occurring in Sardinia, Italy. To obtain a broader view of Halimium mycorrhizal and ecological potential, we compiled a comprehensive and up-to-date checklist of fungal species reported to establish ectomycorrhizae on Halimium spp. on the basis of field observations, molecular approaches, and mycorrhiza synthesis. Our list comprises 154 records, corresponding to 102 fungal species and 35 genera, revealing a significant diversity of the Halimium ectomycorrhizal mycobiota. Key ectomycorrhizal genera like Russula, Lactarius/Lactifluus, Amanita, Inocybe, and Cortinarius account for more than half of all mycobionts. A large proportion of Halimium fungal species are shared with other host plants in various ecological settings, suggesting a critical role of common mycorrhizal networks in the function played by this shrub in various Mediterranean ecosystems.

Full text

ORIGINAL ARTICLE
Halimium as an ectomycorrhizal symbiont: new records
and an appreciation of known fungal diversity
Marco Leonardi
1
&Ariadne Nóbrega Marinho Furtado
2
&Ornella Comandini
3
&József Geml
4
&Andrea C. Rinaldi
5
Received: 2 July 2020 /Revised: 15 October 2020 /A ccepted: 19 October 2020
#The Author(s) 2020
Abstract
Halimium is a genus of Cistaceae, containing a small group of shrub species found in open vegetation types and in degraded
forest patches throughout the western and central Mediterranean region. We recently described the morpho-anatomical features
of the ectomycorrhizae formed by Scleroderma meridionale on Halimium halimifolium, but the mycorrhizal biology of this host
plant genus is still largely unexplored. Here, we report new data on the ectomycorrhizal fungal symbionts of Halimium,basedon
the collection of sporocarps and ectomycorrhizal root tips in pure stands occurring in Sardinia, Italy. To obtain a broader view of
Halimium mycorrhizal and ecological potential, we compiled a comprehensive and up-to-date checklist of fungal species
reported to establish ectomycorrhizae on Halimium spp. on the basis of field observations, molecular approaches, and mycorrhiza
synthesis.Our list comprises 154 records, corresponding to102 fungal species and 35 genera, revealing a significant diversity of
the Halimium ectomycorrhizal mycobiota. Key ectomycorrhizal genera like Russula,Lactarius/Lactifluus,Amanita,Inocybe,
and Cortinarius account for more than half of all mycobionts. A large proportion of Halimium fungal species are shared with
other host plants in various ecological settings, suggesting a critical role of common mycorrhizal networks in the function played
by this shrub in various Mediterranean ecosystems.
Keywords Cistaceae .Ecological networks .Ectomycorrhiza .Fungal communities .Maquis shrubland
Introduction
Shrublands occupy a specific niche in the Mediterranean bi-
ome, with an increasingly appreciated ecological function. In
particular, plants occurring in this peculiar environment im-
prove water and light regime, protect soil from erosion, and
desertification, and act as “nurse”species for tree seedlings,
thus favoring the establishment of late-successional species
(https://php.radford.edu/~swoodwar/biomes/?page_id=98).
To perform such tasks, the shrubs and small trees that
integrate this vegetation system developed adaptations to
withstand adverse and stressful conditions such as drought
and fire (Rundel and Cowling 2013). The presence of a large
number of ectomycorrhizal fungi, mainly associated with
Cistaceae Juss., is another common trait of Mediterranean
shrublands. The role played by ectomycorrhizal fungi in opti-
mizing plant fitness and increasing nutrients’availability in a
wide range of terrestrial ecosystems, especially where cold
and dry conditions limit decomposition, is largely appreciated
(Smith and Read 1997). Cistus is the dominant
ectomycorrhizal host plant in Mediterranean shrublands.
Over 250 fungal species belonging to 40 genera have been
reported to be associated with Cistus,with35host-specific
species; members of the Cortinariaceae and Russulaceae
make up the most of both generalist and Cistus-specific
mycobionts (Comandini et al. 2006; Loizides 2016).
The genus Halimium (Dunal) Spach belongs to the
Cistaceae (Page 2017), with 13 accepted species of evergreen
Section Editor: Dominik Begerow
*Andrea C. Rinaldi
rinaldi@unica.it
1
Department of Life, Health and Environmental Sciences, University
of L’Aquila, I-67100 Coppito, AQ, Italy
2
Departamento de Botânica, Campus Universitário Reitor João David
Ferreira Lima Centro de Ciências Biológicas, Universidade Federal
de Santa Catarina, Trindade, Florianópolis, SC 88040-960, Brazil
3
Department of Life Sciences and the Environment, University of
Cagliari, I-09042 Monserrato, CA, Italy
4
MTA-EKE Lendület Environmental Microbiome Research Group,
Eszterházy Károly University, Leányka u. 6., Eger H-3300, Hungary
5
Department of Biomedical Sciences, University of Cagliari,
I-09042 Monserrato, CA, Italy
https://doi.org/10.1007/s11557-020-01641-0
Mycological Progress (2020) 19:1495–1509

or semi-deciduous small-to-large shrubs (http://www.
theplantlist.org/1.1/browse/A/Cistaceae/Halimium/).
However, these include H. brasiliense (Lam.) Grosser that is
considered by other sources a synonym of Crocanthemum
brasiliensis Spach and that has a disjunct distribution (in the
New World) with respect to all other known species of
Halimium (https://www.gbif.org/species/3596090), and
Halimium ×pauanum Font Quer, a naturally occurring
hybrid between H. lasiocalycinum (Boiss. & Reuter) Engler
& Pax and H. lasianthum (Lam.) Spach (Soriano 2008). A
new species, H. voldii Kit Tan, Perdetz. & Raus has been
recently described from Greece (Greuter and Raus 2000);
however, both the status of this taxon and that of H. syriacum
K. Koch, reported from subalpine levels in Lebanon and
Syria, are still unresolved. Halimium is closely related to
Cistus; some botanists in the past have considered Halimium
species as belonging to Cistus (e.g., Demoly 2006), but the
most recent molecular phylogenetic analyses have clearly
shown the two genera as distinct (Guzmán and Vargas 2005,
2009; Civeyrel et al. 2011). The two genera overlap largely in
distribution within the Mediterranean basin although
Halimium is restricted to the western partof the floristic region
(Civeyrel et al. 2011)(Fig.1). Halimium species occur usually
in open vegetation types, like matorral shrublands and
garrigues, but they can also been found in degraded forest
patches, at the verges of woods, abandoned fields,
pasturelands, and on coastal sandy areas and dry dunes
(Zunzunegui et al. 2002,2009).
The mycorrhizal biology of Halimium is poorly known.
The genus may form ectomycorrhizae and possibly vesic-
ular arbuscular mycorrhizae (Camprubi et al. 2011;
Buscardo et al. 2012; Beddiar et al. 2015). To expand the
current knowledge of mycorrhizal interactions of
Halimium, we started a research program focusing on the
isolation and full characterization of the ectomycorrhizae
formed by the fungal symbionts associated with Halimium
spp. We recently described, for the first time, the morpho-
anatomical features of an ectomycorrhiza on Halimium,
formed by Scleroderma meridionale Demoulin &
Malençon on Halimium halimifolium (L.) Willk.
(Leonardi et al. 2018). In the current paper, we report
new data on Halimium mycobionts, as observed in pure
stands occurring in Sardinia, Italy, through both sporo-
carps and ectomycorrhizal root tip collections. Also, we
provide a comprehensive and up-to-date checklist of fun-
gal species reported to establish ectomycorrhizae on
Halimium spp. on the basis of field observations, molecu-
lar approaches, and mycorrhiza synthesis, a type of infor-
mation that is widely dispersed in the mycological litera-
ture, with no specific account existing on the topic. The
data presented here reveal a high diversity of the Halimium
ectomycorrhizal mycobiota.
Fig. 1 Distribution map of Halimium spp. Occurrence data from the Global Biodiversity Information Facility (https://www.gbif.org/)
1496 Mycol Progress (2020) 19:1495–1509

Materials and methods
Collecting site and fungal sampling
Sporocarps of ectomycorrhizal fungi were harvested in a
costal sandy area (from 39° 15′17.42″N, 8° 24′32.75″E
to 39° 15′46.07″N, 8° 24′46.89″E and from 58 to 123 m
asl) close to Gonnesa, about 70 km west of Cagliari,
Sardinia, Italy. Collection surveys were conducted weekly
during growing season (October–January) and monthly
during the rest of the year, from 2015 through 2019.
Sporocarps were photographed in situ and identified on
the basis of published descriptions of macroscopic and mi-
croscopic characters. Fungal species names retrieved from
literature were verified for nomenclatural and taxonomic
synonyms in Index Fungorum (http://www.
indexfungorum.org)andMycoBank(http://www.
mycobank.org) and current names adopted. The collection
site is characterized by extended stands H. halimifolium
(Fig. 2) that here occurs practically in pure form. No
other potential ECM host plants are present on the site,
with the exception of a few scattered Cistus salviifolius L.
shrubs. For ectomycorrhizae, 40 soil cores (about 20 ×
20 × 20 cm) were excavated randomly in proximity of
Halimium shrubs (not underneath sporocarps), at least
5 m apart from each other. Soil cores were immersed
overnight in water, and ectomycorrhizal roots were
carefully separated under a dissecting microscope.
Ectomycorrhizae were classified into morphotypes
following the methods and indications of Agerer (1991),
and several tips for each type were immediately transferred
into 90% EtOH and stored at −20 °C for subsequent DNA
analysis or fixed in 2.5% (v/v) glutaraldehyde in 10 mM
Na-phosphate buffer (pH 7.2) for morpho-anatomical de-
scription of characterizing features. Reference materials for
sporocarps and ectomycorrhizae are deposited in CAG, at
the collection of the Department of Biomedical Sciences,
University of Cagliari, Cagliari, Italy.
Molecular characterization of the fungi
Identification of sporocarps and ectomycorrhizae using a mo-
lecular approach was based on PCR amplification and se-
quencing of the complete internal transcribed spacer (ITS)
regions in nuclear ribosomal DNA (Gardes and Bruns
1993). Genomic DNAs of the sporocarps were isolated from
20 mg of each dried sample using DNeasy Plant Mini Kit
(Qiagen, Hilden, Germany), and the ITS amplifications were
performed following the protocol reported by Leonardi et al.
(2005). A direct PCR approach was applied to identify
ectomycorrhizal tips isolated from soil samples as described
by Iotti and Zambonelli (2006). Three ectomycorrhizal tips
were selected as PCR targets and directly amplified using
ITS1F/ITS4 primer pairs (White et al. 1990; Gardes and
Bruns 1993). Two microliters of 20 mg/ml BSA (bovine se-
rum albumin) solution (Fermentas, Vilnius) was added to each
reaction tube to prevent PCR inhibition (Leonardi et al. 2013).
The amplified products were purified using the QIAquick
PCR Purification Kit (Qiagen, Milan, Italy) and sequenced
by Eurofins Genomics service (Ebersberg, Germany).
Sequence-based fungal identification was performed follow-
ing the indications and recommendations reported in
Hofstetter et al. (2019). Sequences of sporocarps and
ectomycorrhizae are deposited in GenBank (https://www.
ncbi.nlm.nih.gov/genbank/) under accession numbers
specified in Table 1. In selected cases, to confirm the
identity of the host shrub roots, the plastid trnL region of
ECM root tip DNA was amplified using primer pairs trnC/
trnD following Tedersoo et al. (2008). In these cases, the
chloroplast trnL region obtained by PCR amplification of
DNA extract from H. halimifolium leaves was used as positive
control.
Compiling the list of records
Data on the association between Halimium spp. and
ectomycorrhiza-forming fungi presented here are largely
Fig. 2 Halimiun halimifolium, Cistaceae, in southwestern Sardinia. aPlant in blossom. bView of ECM collection stand. cFlower close-up
1497Mycol Progress (2020) 19:1495–1509

Table 1 Ectomycorrhizal fungi reported to be associated with Halimium spp.
Species Host (Halimium) Reference Sequence
Ascomycota
Cenococcum geophilum Fr. H. lasianthum,
H. ocymoides
Buscardo et al. 2012 (ECM) HQ625444
H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY595999
H. halimifolium This study (ECM)
Terfezia boudieri Chatin
a
H. halimifolium Chevalier 2014
Terfezia dunensis Ant. Rodr., Cabero, Luque &
Morte
H. halimifolium Crous et al. 2019 MN438324
Terfezia spp. H. halimifolium Chatin 1891
H. halimifolium Olaizola Suárez et al. 2012
Terfezia sp. 1 H. ocymoides Buscardo et al. 2012 (ECM) HQ625472
Terfezia sp. 2 H. lasianthum Buscardo et al. 2012 (ECM) HQ625473
Tuber oligospermum Tul.&C.Tul.(Trappe)
b#
H. halimifolium This study (ECM) MT594491
Basidiomycota
Alessioporus ichnusanus (Alessio, Galli & Littini)
Gelardi, Vizzini & Simonini
#
H. halimifolium This study MT594492
Amanita cistetorum Contu & Pacioni* H. halimifolium Moreau et al. 2007a, Moreau et al. 2007b
Amanita citrina (Schaeff.:Fr.) Pers. H. halimifolium Moreau et al. 2007a
H. ocymoides Buscardo et al. 2012 (ECM) HQ625456
Amanita curtipes E.-J. Gilbert f. curtipes
#
H. halimifolium Moreau et al. 2007a
Amanita gilbertii Beauseign
#
H. halimifolium This study MT594493
Amanita gracilior Bas & Honrubia Halimium sp. Moreno-Arroyo 2004
Amanita malleata (Piane ex Bon) Contu H. halimifolium Taudiere et al. 2015
Amanita muscaria var. inzengae Neville &
Poumarat
#
H. halimifolium Moreau et al. 2007a
Amanita pantherina (D.C.:Fr.) Krombh
#
H. halimifolium Moreau et al. 2007a
H. halimifolium This study MT594494
Amanita ponderosa Malençon & R. Heim
#
Halimium sp. Moreno-Arroyo 2004
Amanita rubescens (Pers.:Fr.) Gray
#
Halimium sp. Moreno-Arroyo 2004
Amanita torrendii Justo
#
Halimium sp. Moreno-Arroyo 2004
c
Amanitavaginataf.alba(Bull.) Vesely H. halimifolium Taudiere et al. 2015
Amphinema sp. H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY595998
Astraeus hygrometricus (Pers.:Pers.) Morgan
#
Halimium sp. Moreno-Arroyo 2004
H. halimifolium Moreau et al. 2007a
H. halimifolium This study MT594495
H. halimifolium This study (ECM) MT594496
Boletus aereus Bull.:Fr.
#
H. alyssoides Martínez de Azagra Paredes et al. 1998
H. lasianthum Oria-De-Rueda et al. 2008,2009
H. ocymoides,
H. viscosum
Martínez de Azagra Paredes et al. 1998
Boletus edulis Bull.:Fr.
#
H. halimifolium Moreau et al. 2007a
H. lasianthum Oria-De-Rueda et al. 2005,2008,2009
H. alyssoides Dentinger et al. 2010 EU231946
Boletus sp. H. halimifolium This study MT594497
Cantharellus cfr. pallens Pilát H. halimifolium This study
Cantharellus subpruinosus Eyssart. & Buyck
d
H. halimifolium Moreau et al. 2007a
Coltricia perennis (L.:Fr.) Murrill H. halimifolium Moreau et al. 2007a
Coltricia cfr. perennis (L.:Fr.) Murrill H. halimifolium This study MT594498
H. halimifolium This study MT594499
Cortinarius candelaris Fr. H. halimifolium This study MT594500
Cortinarius cedretorum var. halimiorum Brotzu &
Peintner
H. halimifolium Brotzu and Peintner 2009 AY900018
e
Cortinarius coeruleopallescens Contu* H. halimifolium This study MT594501
Cortinarius maculatocaespitosus Bidaud H. halimifolium This study MT594502
H. halimifolium This study MT594503
Cortinarius palazonianus Vila, A. Ortega &
Fern.-Brime
H. halimifolium Fernandez-Brime et al. 2014
Cortinarius rigens (Pers.) Fr. H. halimifolium This study MT594504
Cortinarius scobinaceus Malençon & Bertault* H. halimifolium Moreau et al. 2007a
f
,Moreauetal.2007b
1498 Mycol Progress (2020) 19:1495–1509

Table 1 (continued)
Species Host (Halimium) Reference Sequence
Cortinarius variiformis Malençon
#
H. halimifolium This study MT594505
H. halimifolium This study MT594506
Descolea maculata Bougher
g
H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY654754
Gyroporus pseudolacteus G. Moreno,
Carlavilla, Heykoop, Manjón & Vizzini
H. halimifolium This study MT594507
Hebeloma cistophilum Maire* H. halimifolium Moreau et al. 2007a,Moreauetal.2007b,
Eberhardt et al. 2009
H. halimifolium This study MT594508
H. lasianthum,
H. ocymoides
Buscardo et al. 2012 (ECM) HQ625447
Hebeloma cylindrosporum Romag.
#
Halimium sp. Moreno-Arroyo 2004
Hebeloma dunense L. Corb. & R. Heim Halimium sp. Moreno-Arroyo 2004
Hortiboletus rubellus (Krombh.) Simonini,
Vizzini & Gelardi
H. halimifolium This study MT594509
Hygrophorus chrysodon (Batsch:Fr.) Fr.
#
H. halimifolium This study MT594510
Hygrophorus cfr. eburneus (Bull.) Fr.
#
H. halimifolium This study MT594511
Inocybe asterospora Quél. Halimium sp.
H. halimifolium
Moreno-Arroyo 2004
Inocybe calida Velen. H. halimifolium Moreno-Arroyo 2004
h
Inocybe corydalina Quél. Halimium sp. Moreno-Arroyo 2004
Inocybe halophila R. Heim.
i
H. halimifolium Moreau et al. 2007a,Moreauetal.2007b
Inocybe lacera (Fr.) P. Kumm. H. halimifolium Moreno-Arroyo 2004
Inocybe pruinosa R. Heim
#
Halimium sp. Moreno-Arroyo 2004
Inocybe tigrina Heim H. halimifolium This study MT594512
H. halimifolium This study MT594513
H. halimifolium This study MT594514
Inocybe sp. 1 H. halimifolium This study MT594515
Inocybe sp. 2 H. halimifolium This study MT594516
Inocybe sp. 3 H. halimifolium This study (ECM) MT594517
H. halimifolium This study (ECM) MT594518
Laccaria bicolor (Maire) P.D. Orton
#
H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY655010
Laccaria proxima (Boud.) Pat.* Halimium sp. Moreno-Arroyo 2004
Laccaria sp. H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY655006
Lactarius cistophilus Bon & Trimbach* H. halimifolium Leonardi et al. 2018 KU885433
H. halimifolium This study MT594519
Lactarius deliciosus (L.) Gray H. halimifolium de Carvalho 2016 (sECM),
Albuquerque-Martins et al. 2019 (sECM)
Lactarius giennensis (Mor.-Arr. et al.) Pierotti
#
H. alyssoides,
H. ocymoides
Vidal et al. 2019
Lactarius hepaticus Plowr.
l
H. lasianthum,
H. ocymoides
Buscardo et al. 2012 (ECM) HQ625465
H. halimifolium This study MT594520
H. halimifolium This study (ECM) MT594521
H. halimifolium This study (ECM) MT594522
Lactarius pseudoscrobiculatus Basso, Neville &
Poumarat
H. halimifolium Moreau et al. 2007a
Lactarius subdulcis (Pers.) Gray
?
H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY681468
Lactarius tesquorum Malençon* H. halimifolium This study MT594523
Lactifluus brunneoviolascens (Bon) Verbeken H. halimifolium Leonardi et al. 2018 KU885434
m
H. halimifolium This study
Lactifluus rugatus Kühn. & Romagn.
#
H. halimifolium This study MT594524
H. halimifolium This study (ECM) MT594525
Leccinellum corsicum (Rolland) Bresinsky &
Manfr. Binder*
H. halimifolium Moreau et al. 2007a
n
H. halimifolium This study MT594526
H. halimifolium This study MT594527
Paxillus ammoniavirescens Contu & Dessì
#
H. halimifolium This study MT594528
Pisolithus arrhizus (Scop.) Rauschert
#
Halimium sp. Moreno-Arroyo 2004
H. halimifolium Moreau et al. 2007a
Pisolithus sp. 1
o
H. halimifolium This study MT594529
1499Mycol Progress (2020) 19:1495–1509

Table 1 (continued)
Species Host (Halimium) Reference Sequence
Pisolithus sp. 2 H. halimifolium This study (ECM) MT594530
Rhizopogon luteolus Fr.
#
Halimium sp. Moreno-Arroyo 2004
H. ocymoides Buscardo et al. 2012 (ECM) HQ625448
Rhizopogon roseolus (Corda) Th. Fr.
#
H. ocymoides Buscardo et al. 2012 (ECM) HQ625451
Russula ammophila (J.M. Vidal & Calonge)
Trappe & T.F. Elliott
Halimium sp.Moreno-Arroyo 2004
p
Halimium sp. Moreno-Arroyo et al. 2005
p
Halimium sp. Vidal et al. 2002
p
AJ438037
Halimium sp. Vidal et al. 2019 MK105623
H. halimifolium Vidal et al. 2019
Russula amoenicolor Romagn. H. halimifolium Moreau et al. 2007a
Russula cistoadelpha M.M. Moser & Trimbach* H. halimifolium This study
Russula densifolia Secr. ex Gillet H. lasianthum Buscardo et al. 2012 (ECM) HQ625470
Russula littoralis Romagn. H. halimifolium Moreau et al. 2007a
Russula monspeliensis Sarnari* H. halimifolium This study MT594531
Russula odorata Romagn.
#
H. halimifolium This study MT594532
H. halimifolium This study MT594533
H. halimifolium This study MT594534
H. halimifolium This study (ECM) MT594535
Russula praetervisa Sarnari
#
H. halimifolium This study (ECM) MT594536
Russula sardonia Fr. H. ocymoides Buscardo et al. 2012 (ECM)
q
HQ625452
Russula tyrrhenica Sarnari* H. halimifolium Moreau et al. 2007a
Russula vinaceodora (Calonge & J.M. Vidal)
Trappe & T.F. Elliot
Halimium sp.Moreno-Arroyo et al. 2005
r
Halimium sp. Vidal et al. 2002
p
, Vidal et al. 2019 AJ438034
Russula sp. H. halimifolium Carvalho et al. 2018 (ECM) LT746014
Russula sp. 1 H. halimifolium This study (ECM) MT594537
Scleroderma citrinum Pers. H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY694393
Scleroderma meridionale Demoulin & Malençon
#
Halimium sp.Moreno-Arroyo 2004
H. halimifolium Leonardi et al. 2018 MG264160
H. halimifolium Leonardi et al. 2018 (ECM) MG367369
H. halimifolium This study MT594538
Scleroderma polyrhizum (J.F. Gmel) Pers. H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY693661
Scleroderma sp. H. halimifolium This study MT594539
Serendipita vermifera (Oberw.) P. Roberts H. halimifolium de Carvalho 2016 (ECM)
st
H. halimifolium Carvalho et al. 2018 (ECM)
s
LT746013
Thelephora cfr. caryophyllea (Schaeff.) Pers.
#
H. halimifolium This study
Thelephora terrestris Ehrh.
#
H. halimifolium Moreau et al. 2007a
H. halimifolium This study MT594540
H. halimifolium This study (ECM) MT594541
H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY693686
H. lasianthum,
H. ocymoides
Buscardo et al. 2012 (ECM) HQ625443
Tomentella badia (Link) Stalpers H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY693714
Tomentella terrestris (Berk. & Broome) M.J.
Larsen
H. ocymoides Buscardo et al. 2012 (ECM) HQ625474
Tomentella sp. H. halimifolium Carvalho et al. 2018 (ECM) LT746015
Tomentellopsis submollis (Svrček) Hjortstam H. lasianthum Santolamazza-Carbone et al. 2019 (ECM) KY693726
Tomentellopsis sp.H.ocymoidesBuscardo et al. 2012 (ECM) HQ625483
Tricholoma equestre (L.:Fr.) P. Kumm. Halimium sp. Moreno-Arroyo 2004
H. halimifolium de Carvalho 2016 (sECM), Albuquerque-Martins et al.
2019 (sECM)
Tricholoma portentosum (Fr.) Quél H. halimifolium de Carvalho 2016 (sECM), Albuquerque-Martins et al.
2019 (sECM)
Tubariomyces hygrophoroides Esteve-Rav.,
P.-A. Moreau & C.E. Hermos
H. halimifolium Alvarado et al. 2010
Tubariomyces inexpectata (M. Villarreal,
Esteve-Raventós, Heykoop & E. Horak)
Esteve-Raventós & Matheny
H. halimifolium Moreau et al. 2007a
u
Tylospora sp. H. halimifolium de Carvalho 2016 (ECM)
t
This study MT594542
1500 Mycol Progress (2020) 19:1495–1509

based on reports of field observations of sporocarps associa-
tions with potential hosts. The dataset contains both personal
collections and observations and information collated from a
variety of published and web-based sources. Literature data-
bases available to authors (e.g., Agricola, Scopus, PubMed,
ISI Web of Science, ResearchGate) were searched for articles
on Halimium and associated mycobionts. Sequences of
Halimium ECM fungi were retrieved from either GenBank
or UNITE. Fungal taxa belonging to genera for which the
mycorrhizal status is currently uncertain were not listed (for
a comprehensive list of ectomycorrhizal fungal genera and the
criteria used to ascertain mycorrhizal status, see Rinaldi et al.
2008 and Comandini et al. 2012). Only records clearly men-
tioning (potential) Halimium hosts were included in the data
matrix (this includes records from mixed Cistus/Halimium
stands). Evidence from studies on the morpho-anatomical
and/or molecular characterization of ectomycorrhizae formed
by fungal species on Halimium spp. were also inserted in the
data set, excluding uncultured fungus sequences and fungal
species not identified at least at genus level. In addition to
studies concerning naturally occurring, field-collected mycor-
rhizae, data coming from synthesized mycorrhizae were also
considered, although it must be stressed that associations in-
duced in laboratory experiments may not occur under field
conditions. Despite all efforts to cover as many bibliographic
sources as possible, our literature survey might clearly be par-
tial and incomplete. Reports of putative mycorrhizal relation-
ships based solely on sporocarps associations rather than con-
firmed by direct inspection of ectomycorrhizae are obviously
subject to an unquantifiable degree of error, especially when
Table 1 (continued)
Species Host (Halimium) Reference Sequence
Xerocomellus redeuilhii A.F.S.
Taylor, U. Eberh., Simonini, Gelardi & Vizzini
H. halimifolium
Zygomycota
Youngiomyces multiplex (Thaxt.) Y.J. Yao H. alyssoides Vidal et al. 1997
ECM description or report of naturally occurring ectomycorrhizae, and/or sequence isolated from ECM or roots. All other records are about sporocarp
collections, if not specified otherwise; sECM description or report of synthesized ectomycorrhizae
§
For names of taxa and synonymy, we followed Index Fungorum (http://www.indexfungorum.org/) and MycoBank (http://www.mycobank.org). The
higher classification system used in this paper is that outlined by Kirk et al. (2008)intheDictionary of the Fungi
*Usually reported as specific or typical Cistus mycobiont (see Comandini et al. 2006)
#
Previously reported as associated with Cistus (see Comandini et al. 2006; Gelardi et al. 2014; Loizides 2016)
?
Dubious or suspect record
a
Often reported as associated with Helianthemum spp. (see Loizides 2016)
b
The status of the close T. asa is still unclear (see Index Fungorum and Boutahir et al. 2013)
c
As Torrendia pulchella Bres.
d
Now considered a synonym of C. pallens (see Olariaga et al. 2017)
e
Deposited as Cortinarius halimiorum
f
Reported by Moreau et al. (2007a)as=C. belleri M.M. Moser. See also Ortega et al. 2006
g
Usually associated with Eucalyptus and introduced in Europe through reforestations (see Santolamazza-Carbone et al. 2019)
h
As Inocybe brunneorufa Stangl & J. Veselsky
i
Sometimes reported as a synonym of I. pruinosa R. Heim (see [MB#252517])
l
Usually reported as associated with Pinus (e.g., Basso 1999
m
Deposited as Lactifluus luteolus
n
As Leccinum corsicum (Rolland) Sing
o
In the Mediterranean region, Pisolithus most likely occurs as a species complex, not completely resolved yet (see Díez et al. 2001;Martinetal.2002;
Lebel et al. 2018)
p
As Macowanites ammophilus (J.M. Vidal & Calonge)J.M. Vidal & Calonge, usually in dunal systems with Pinus pinea,P. pinaster,andCistus (see
also http://www.micobotanicajaen.com/Revista/Articulos/DMerinoA/SetasDunas002/MacowanitesAmmophilus.pdf)
q
As Russula drimeia Cooke
r
As Macowanites vinaceodorus Calonge & J.M. Vidal, usually in dunal systems with Pinus pinea and Cistus (Moreno-Arroyo et al. 2005)
s
As Sebacina vermifera (Oberw.)
t
Sequence not deposited
u
As Inocybe inexpectata Villarreal, Esteve-Rav., Heykoop & E. Horak in Moreau et al. 2007a
1501Mycol Progress (2020) 19:1495–1509

more than one potential plant hosts are present (e.g., mixed
Halimium stands with Cistus,Pinus,and/orQuercus). Finally,
the identification of some fungi in the references that we have
considered may not be correct.
Results
The Halimium ectomycorrhizal guild
Our effort to gauge the diversity of ectomycorrhizal fungi
linked to Halimium, through both direct field sampling and
the compendium of literature records, resulted in 154 listed
entries, corresponding to 102 species belonging to 35 genera
from Ascomycota, Basidiomycota, and Zygomycota
(Table 1). This tally excludes a few cases of possible synon-
ymy, e.g., Inocybe halophila R. Heim = I. pruinosa R. Heim
and Cantharellus cfr. pallens =C. subpruinosus Eyssart. &
Buyck, and the dubious record of Lactarius subdulcis (Pers.)
Gray, a known Fagus symbiont whose sequence was proba-
bly misbranded and it is likely to be L. hepaticus Plowr. Fifty-
seven of the listed records, which refer to 41 different species,
were provided by our field work in Halimium plots in south-
western Sardinia, Italy; of these, 29 species are reported here
for the first time as linked to Halimium. Most of the ecologi-
cally key ectomycorrhizal fungal genera are represented in the
list, with Russula (13 species), Amanita (12 spp.), Inocybe (10
spp.), Lactarius/Lactifluus (9 spp., including the synthesized
ECMs of L. deliciosus (L.) Gray, see below), and Cortinarius
(8 spp.), accounting for more than half of all species. As in
other genera of Cistaceae (e.g., Cistus and Helianthemum), it
is apparent from the entries in the list that hypogeous ascomy-
cetes make a significant part of the Halimium ectomycorrhizal
contingent (Table 1). Several Terfezia species, including the
newly described T. dunensis Ant. Rodr., Cabero, Luque &
Morte (Crous et al. 2019), were reported as associated with
Halimium. In our plots, we isolated the ECMs formed by
Tuber oligospermum Tul. & C. Tul. (Trappe) on
H. halimifolium (see Fig. 3e), molecularly confirming the
identity of host plant (data not shown). Belonging to the
Puberulum group, or the so-called whitish truffles,
T. oligospermum hasbeenreportedpreviouslyasaQuercus
and Cistus mycobiont (Comandini et al. 2006; Lancellotti
et al. 2016), and it is the first Tuber species ever to be proven
to form ECMs with Halimium.
While the vast majority of records of Halimium-linked
ectomycorrhizal fungi derives from aboveground observa-
tions of sporocarps, a fairly good number of collections and
molecular characterizations of ECM tips have permitted to
open a window on the belowground reality. In particular, the
works conducted by Buscardo et al. (2012), de Carvalho
(2016), and Carvalho et al. (2018)inPinus-dominated forests
with understorey shrubs in Portugal, and by Santolamazza-
Carbone et al. (2019) in mixed shrublands in northwestern
Spain, have resulted in the molecular identification of an array
of ectomycorrhizal fungi in the Halimium spp.roots. These
included Cenococcum geophilum Fr., Terfezia spp., Amanita
citrina (Schaeff.:Fr.) Pers., Amphinema sp., Descolea
maculata Bougher, Hebeloma cistophilum Maire, Laccaria
spp., Lactarius hepaticus,Rhizopogon spp., Russula spp.,
Scleroderma spp., Serendipita vermifera (Oberw.) P.
Roberts, Thelephora terrestris Ehrh., Tomentella spp.,
Tomentellopsis spp., and Tylospora sp. (Table 1). In addition,
Albuquerque-Martins et al. (2019) described the synthesized
ECMs of H. halimifolium with Tricholoma equestre (L.:Fr.) P.
Kumm., T. portentosum (Fr.) Quél, and Lactarius deliciosus.
However, it is well-known that successful pure-culture syn-
thesis of ectomycorrhizae not necessarily reflects naturally
occurring partnerships between given host plant-mycobiont
pairs (although Halimium-linked T. equestre has been collect-
ed also in the field). During our study, through random sam-
pling of soil in the proximity of H. halimifolium shrubs, we
isolated eleven distinct morphotypes (Table 1;Fig.3). In six
cases (Astraeus hygrometricus (Pers.) Morgan, Lactarius
hepaticus,Lactifluus rugatus Kühn. & Romagn., Russula
odorata Romagn., Scleroderma meridionale,and
Thelephora terrestris), sporocarps of the same species were
also collected. Five other species (Tuber oligospermum,
Inocybe sp. 3, Pisolithus sp. 2, Russula praetervisa Sarnari,
and Russula sp.) were collected only belowground. The full
morphological characterization of selected morphotypes is un-
der way, and will be presented in a complimentary work.
WalkinghandinhandwithHalimium
Some of the mycorrhizal fungi we found associated with
Halimium deserve a special mention and further notes. One
of the most common ectomycorrhizal fungal species present
in our H. halimifolium plots was Scleroderma meridionale
(MycoBank MB#323250). Basidiomata of this species are
large, globose, characterized by a smooth-to-finely
furfuraceous peridium of an intense sulfur yellow color, which
becomes brighter in the long pseudostipe, usually immersed
deep in the soil (Fig. 4a). The habit is solitary, occasionally
gregarious, found mostly in sandy soils and dunes. Originally
described on the basis of collections from southern Portugal,
continental France, Corsica, and Morocco, it occurs in all the
Mediterranean basin, including Greece, Macedonia, and
Turkey (Rusevska et al. 2014; Dimou et al. 2016). It is also
reported from North America, from Florida to Arizona, and
Oregon (Guzmán and Ovrebo 2000;Kuo2004,http://www.
svims.ca/council/Sclero.htm). However, the identity of these
collections still awaits confirmation: indeed, preliminary
molecular data seem to indicate that the North American “S.
meridionale”belongs to a distinct, so far undescribed, taxon
(D. Puddu, M. Leonardi, A.C. Rinaldi, unpublished data).
1502 Mycol Progress (2020) 19:1495–1509

Based on field observations, S. meridionale has been reported
as associated with both evergreen and deciduous species of
Quercus,Pinus,andalsoCistus (Comandini et al. 2006;
Phosri et al. 2009; Dimou et al. 2016). We recently described
the morpho-anatomical features of the ectomycorrhizae
formed by S. meridionale on H. halimifolium, with the help
of confocal laser scanning microscopy; the mycobiont and
host plant identity from the ECM root tips were verified
through molecular tools (Leonardi et al. 2018). This was the
first description of an ectomycorrhiza on Halimium. The fea-
tures of this ECM—felty mantle surface, whitish with silver
patches, mantle surface characterized by a network of
branched hyphae organized in hyphal bundles, small dimen-
sion of mycorrhizal system—are similar to those reported for
the few described naturally occurring Scleroderma ECMs and
to other ECMs formed by Cistaceae (Leonardi et al. 2018).
Another interesting species recorded in our collection site
was Alessioporus ichnusanus (MB#808530). The taxon cor-
responds to a boletoid species recently segregated from
Xerocomus Quél. to typify the new genus Alessioporus
Gelardi, Vizzini & Simonini which currently accommodates
two species. Its type and epitype were collected in Sardinia in
1980 (Galli 1981) and in 2003 (Gelardi et al. 2014), respec-
tively, in Quercus spp. and Cistus spp. forests, in the province
of Medio Campidano, 60 km from our Halimium plots. In
addition to the type collections, the taxon has been recorded
in different localities in Sardinia, as well as in Sicily, conti-
nental Italy (Brotzu 1988;Alessio1991; Brotzu and Colomo
2009; Gelardi 2010; Illice et al. 2011) and other
Mediterranean countries, as France (Eyssartier and Roux
2011), Greece (Polemis et al. 2012), and Spain (Muñoz
2005). Alessioporus ichnusanus can be recognized by the
ochraceous-brown, dark olive-brown-to-copper-brown pileus
with brownish-black fibrils (Fig. 4b). But one of the most
important morphological character that define this species is
a narrow pseudo-annulus in the middle part of the stipe
formed by the remnants of the connection between the pileus
margin and the stipe cortex during the primordial stage (Galli
2013). Currently, Alessioporus ichnusanus is considered an
uncommon or rare species that has recently been included in
the Red List of Italian macrofungi as an endangered species
(Rossi et al. 2013) and in the IUCN red list as vulnerable
(Persiani 2019;Angelinietal.2020).
Keeping with the Boletales, Gyroporus pseudolacteus G.
Moreno, Carlavilla, Heykoop, Manjón & Vizzini (MycoBank
MB#356882) is an interesting finding. This species has been
recently described from a material collected in Spain, on
sandy soil under Pinus pinaster (Crous et al. 2016). To the
best of our knowledge, this is the first confirmed record of this
species not only for Sardinia but also for Italy. Gyroporus
pseudolacteus can be distinguished from the common and
closely related Gyroporus cyanescens (Bull.) Quél. by its larg-
er habit, the longer stipe in relation to the pileus diameter, and
the “deep and persistently indigo blue when handled or
bruised”(Crous et al. 2016)(Fig.4c). According to Vizzini
and co-workers, G. cyanescens should be considered a com-
plex of cryptic species (Vizzini et al. 2015) which is being
unraveled with the help of molecular tools (see Crous et al.
2017), even though some of these taxa are still being treated as
synonyms by some fungal names databases. While this is the
first mention of Halimium as the probable host, the putative
association of Gyroporus with cistaceous plants is not unprec-
edented. Although the six (not universally accepted) known
European species of Gyroporus—G. ammophilus (M.L.
Castro & L. Freire) M.L. Castro & L. Freire; G. castaneus
(Bull.) Quél.; G. cyanescens;G. lacteus Quél.;
G. pseudocyanescens G. Moreno, Carlavilla, Heykoop,
Manjón & Vizzini; and G. pseudolacteus—are usually report-
ed from under coniferous (Pinus) or decidous (Castanea,
Fagus,Quercus) hosts (Vizzini et al. 2015; Crous et al.
2016,2017), G. ammophilus was found along the Atlantic
coast of the Iberian Peninsula “on fixed dunes in association
with Pinus spp., or, less frequently with other trees and shrubs,
such as Quercus suber L. and Cistus salviaefolius (sic!), on
sandy soils”(Castro and Freire 1995).
Lactarius hepaticus (MycoBank MB#224000) was, by far,
the most common milkcap in our Halimium stands (Fig. 4d).
This was an unexpected finding, since this species belonging
to the subgenus Russularia is commonly associated with
Pinus and, more occasionally, other conifers such as Picea
and Pseudotsuga (Heilmann-Clausen et al. 1998;Basso
1999). Uncommon to rare/absent in northern Europe is more
frequent in Britain, the Netherlands, and, above all, in the
Mediterranean area. This species is characterized by its con-
vex to applanate with a depressed center cap, with liver-brown
color (hence the epithet); the milk is white, turning yellow on a
tissue (Pierotti 2005). Intriguingly, in central Portugal,
L. hepaticus was part of shared ECM networks between un-
derstory shrubs and pine trees in a Pinus-dominated forest,
being detected with molecular tools on the roots of both
Pinus pinaster and Halimium lasianthum and H. ocymoides
(Lam.) Willk. (Buscardo et al. 2012). Along the coastal area in
Sardinia, where our Halimium plots are situated, Pinus stands
are also frequent, originated from extensive reforestation plans
carried out during the last century. We collected L. hepaticus
in these stands as well, where H. halimifolium is frequent both
in the understory and at the edges of the pine forest. Lactarius
hepaticus was abundant as sporocarps among Halimium
shrubs and on their roots in proximity of Pinus,confirming
the existence of shared ECM networks, but it occurred also in
pure Halimium plots distant several kilometers from pine trees
stands, in areas where Pinus, at the best of our knowledge, has
never been present. This suggests colonization of new ECM
plant hosts (like Halimium)byL. hepaticus by means other
than root networking, such as spore dispersal. More work is
underway to investigate L. hepaticus ecological plasticity.
1503Mycol Progress (2020) 19:1495–1509

Lactifluus brunneoviolascens (Bon) Verbeken (MycoBank
MB#564601) is another uncommon species, reported here for
the second time in Sardinia (see Lalli and Pacioni 1992). It
was previously named L. luteolus Peck, which is now known
to be the correct name for a North American species
(Verbeken et al. 2012; De Crop et al. 2017). Both species
belong to the newly erected section Phlebonemi (R. Heim ex
Verbeken) Verbeken (= Lactarius subsect. Luteoli Pacioni &
Lalli) (Verbeken et al. 2012). Lactifluus brunneoviolascens is
easily distinguished in the field by the whitish/whitish-cream
color of the pileus, with velvety cuticle, dry even in very
humid weather, finely crenulated at the edge, stained ocher-
brown with age;the context is firm, whitish then darker ocher-
brownish, with a sweet taste and an unpleasant fishy smell; the
latex is fluid, abundant, opalescent white, immutable if isolat-
ed on glass, slowly but strongly browning in contact with the
lamellae or on absorbent paper (Fig. 4e). We studied two
different collections of this Lactifluus from almost pure
H. halimifolium stands. Another collection was recently re-
corded from southeastern Sardinia, under Quercus (Alberto
Mua, personal communication), a more usual habitat (some-
times it also occurs in mixed Quercus-Pinus forests) for this
species with a prevalently Mediterranean distribution that pre-
fers dry and sandy soils (Basso 1999;Pierotti2002).
Among the various Cortinarius species encountered during
this study and likely linked to Halimium,Cortinarius
coeruleopallescens Contu (MycoBank MB#459976) deserves
a mention (Fig. 4f). This taxon, not uncommon in our plots,
was described in 1999, when Marco Contu raised to species
level a fungus he encountered in Sardinia, and that had been
observed by other researchers 2 years earlier in Spain and
originally thought to be a variety of C. croceocoeruleus
(Pers.) Fr., C. croceocoeruleus var. meridionalis Bidaud, A.
Ortega & Mahiques (Ortega et al. 1997;Contu1999). The
collections from both Spain and Sardinia were associated with
Cistus, while C. croceocoeruleus is typical of central
European coniferous and broadleaved forests. Another species
linked to Halimium and worthy of remark is Cortinarius
cedretorum var. halimiorum Brotzu & Peintner (Mycobank
MB#580057) (Table 1). This beautiful variety in the subgenus
Phlegmacium was described (originally reported in a field
guide as C. halimiorum; see Brotzu and Colomo 2009)on
the basis of material collected on a dune system in the north-
eastern part of Sardinia (Brotzu and Peintner 2009). Despite
the fact that the vegetation system in this case is more complex
than the one present in our H. halimifolium stands, with
psammophile coastal associations where H. halimifolium is
present together with other floristic entities, such as Cistus
spp., Pistacia lentiscus L., Juniperus phoenicea L., and
Arbutus unedo L. (see Arrigoni 1996), the link between this
specific Cortinarius and Halimium was apparent to the re-
searchers (Brotzu and Peintner 2009).
Fig. 3 Habit of some of the
ectomycorrhizal morphotypes
collected under Halimium
halimifolium during this study. a
Astraeus hygrometricus.b
Lactarius hepaticus.cRussula
monspeliensis.dRussula
praetervisa.eTuber
oligospermum
1504 Mycol Progress (2020) 19:1495–1509

Discussion
Using the dataset assembled in Table 1, it is not straightfor-
ward to compare the above- and belowground composition of
Halimium-linked ECM fungal communities. It should be
remarked, indeed, that the dataset contains records from stud-
ies conducted with different goals and methodologies. For
example, with the exception of the present work, studies pro-
viding ECM records did not consider sporocarps at all
(Buscardo et al. 2012; de Carvalho 2016;Carvalhoetal.
2018;Santolamazza-Carboneetal.2019). Conversely, many
sporocarp observations are derived from surveys that
disregarded belowground views. It istechnically easier to col-
lect and identify sporocarps than ECMs, and belowground
diversity tends to be undersampled. To get a clearer picture
of soil and root fungal communities in Halimium scrublands,
we started an ongoing metabarcoding project in our Sardinian
Halimium stands. Preliminary results show the presence on
Halimium roots of additional ECM genera, such as
Geopora,Helvella,andWilcoxina, and species, like
Astraeus telleriae M.P. Martín, Phosri & Watling (Geml
et al., unpublished data). This study, when complete, will ren-
der a more complete view of the composition of belowground
ECM community and its correlation with aboveground
diversity.
So far, no Halimium-specific or preferential ECM
mycobiont has emerged, with the possible exception of
Cortinarius cedretorum var. halimiorum Brotzu & Peintner.
However, since our knowledge of this host plant and its ECM
guild is rudimental, this ecological liaison will most likely be
recognized in the near future, possibly accompanied by the
description of new fungal species. Our failure to identify a
perfect molecular match for several of the sequences obtained
during this study supports this speculation. Nearly 40% of the
species listed in Table 1(41, counting Terfezia spp.) have
been previously reported as Cistus-associated (see
Comandini et al. 2006;Loizides2016). This includes well-
known “Cistus-specific”mycobionts, such as Amanita
cistetorum Contu & Pacioni, Hebeloma cistophilum,
Lactarius cistophilus Bon & Trimbach, Lactarius tesquorum
Malençon (see Nuytinck et al. 2004; Comandini and Rinaldi
2008), and Leccinellum corsicum (Rolland) Bresinsky &
Manfr. Binder. Given the Halimium-Cistus phylogenetic af-
finity, and the co-occurrence of the two host plants in many
ecological settings, the extensive ECM sharing is not particu-
larly surprising, at least when the concept of host-specificity is
applied at the plant family level (Cistaceae). Another cluster
of Halimium mycobionts are also linked to Quercus,onthe
basis of a number of field observations (Leonardi et al. 2016;
Comandini et al. 2018). This group includes Alessioporus
ichnusanus (Alessio, Galli & Littini) Gelardi, Vizzini &
Simonini (also known to be associated to a lesser extent, with
Cistus spp.); Hortiboletus rubellus (Krombh.) Simonini,
Vizzini & Gelardi; Xerocomellus redeuilhii A.F.S. Taylor,
U. Eberh., Simonini, Gelardi & Vizzini; Lactifluus rugatus;
and Scleroderma meridionale. Finally, a bunch of Halimium
symbionts are shared with Pinus, as demonstrated in studies
carried out in Portugal (Buscardo et al. 2012; de Carvalho
2016; Carvalho et al. 2018). Again, “host-specific”Pinus
mycobionts, such as Rhizopogon spp., Russula sardonia Fr.
(= Russula drimeia Cooke), and Lactarius hepaticus, were
detected on both Halimium and Pinus roots, together with
Fig. 4 Sporocarps of selected species discussed in the text. aScleroderma meridionale.bAlessioporus ichnusanus.cGyroporus pseudolacteus.d
Lactarius hepaticus.eLactifluus brunneoviolascens.fCortinarius coeruleopallescens
1505Mycol Progress (2020) 19:1495–1509

more generalist fungal species like Serendipita vermifera
(Oberw.) P. Roberts, Thelephora terrestris,andTomentella
terrestris (Berk. & Broome) M.J. Larsen. In the study in cen-
tral Portugal by Buscardo and colleagues, it is showed that
about 30% of the identified ECM fungal species were com-
mon to pine and Halimium spp., with shared ECM fungal
species representing up to 80% of the total fungal abundance
in some stands (Buscardo et al. 2012). To expand even further
the plasticity of Halimium as ECM host plant, H. lasianthum
was shown to establish symbiotic interactions with the
Australian Descolea maculata Bougher in Spain, spreading
from nearby Eucalyptus plantations (Santolamazza-Carbone
et al. 2019). In Corsica, H. halimifolium was reported to have
a contingent of 12 ECM fungal species, shared in different
proportions with Cistus,Quercus,andPinus, but also with
other host plants like Castanea,Fagus,Corylus,Populus,
Salix,Alnus,Betula,andAbies (Taudiere et al. 2015).
The ability of Cistaceae to develop common mycelial net-
works by sharing ECM fungal partners with neighboring
plants is a crucial ecological trait that has not been appropri-
ately appreciated. As stressed by Randy Molina and Thomas
Horton, “common mycelial networks (CMNs) of mycorrhizal
fungi connecting neighboring host plants affect ecosystem
processes and community dynamics including seedling estab-
lishment, plant succession, and ecosystem resiliency”(Molina
and Horton 2015). Based on our current knowledge of
Halimium and Cistus ECM communities, it is apparent that
these are largely shaped by “ecological specificity”rather than
host-specificity. Despite the fact that both genera have host
preferential (or even exclusive) fungal partners, large part of
their mycorrhizal associations seems rather driven by environ-
mental (soil composition, for example) and biological factors,
like the presence of other host plants in the same or neighbor-
ing areas, thus going beyond host-fungus genetic compatibil-
ity due to co-evolution. Either in pure shrublands, as in our
Sardinian stands, or at the edges or in the understory of
Quercus and Pinus forests, especially when growing on poor
and/or degraded soils, Halimium might thus play a key eco-
logical role, maintaining ECM fungal diversity, favoring veg-
etation succession and dynamics, and assisting ecosystem re-
silience following disturbance, thanks to common mycelial
networks and possibly spore dispersal of ECM mycobionts.
A similar function has been recognized for Cistus. In Spain,
many of the fungal species associated with Cistus ladanifer L.
were found to be shared with Pinus pinaster Aiton, suggesting
a role in the regeneration of Pinus stands after wildfire
(Martín-Pinto et al. 2006). In this context, it is relevant to note
that Cistus and possibly Halimium are dual-mycorrhizal
plants, capable of hosting both arbuscular mycorrhizal and
ectomycorrhizal associations. Several early successional
ECM hosts like Alnus,Populus,andSalix share this feature.
In the Mediterranean ecosystem, Cistaceae definitely play a
major role in secondary succession following major
disturbances like fire (or even human activity). Benefits deriv-
ing from dual-mycorrhizal colonization thus extend from in-
terested plants—endowed with greater survival, growth, and
nutrient uptake—to ecosystems, favoring establishment and
improving survival on adverse sites of connected ECM plants
(Teste et al. 2020).
Conclusions
We are just starting to unveil the complexity of Halimium
mycorrhizal biology and ecology, especially for what con-
cerns host-specificity of associated mycobionts and patterns
of shared mycorrhizal networks with neighboring host plants.
The general poor knowledge of Halimium as an
ectomycorrhizal host has led to relatively few records of po-
tentially associated fungal species based on observations of
sporocarp occurrence. Hopefully, this and other works will
increase the awareness of researchers, providing us in the near
future with fresh data coming from fungal forays. Also, well-
planned molecular studies examining mycorrhizal specificity
at the root tip scale are bound to disclose many details of the
structure and dynamics of Halimium-linked ectomycorrhizal
communities in multiple ecological settings.
Funding Open access funding provided by Università degli Studi di
Cagliari within the CRUI-CARE Agreement. ANMF was supported by
Coordenação de Aperfeiçoamento Pessoal de Nível Superior—Brazil—
Finance Code 001 (CAPES-DS and PDSE fellowship grants).
Data availability All associated data are deposited in public repositories.
Compliance with ethical standards
Conflict of interest The author declares that they have no conflict of
interest.
Ethics approval not applicable.
Consent to participate not applicable.
Consent for publication not applicable.
Code availability not applicable
Open Access This article is licensed under a Creative Commons
Attribution 4.0 International License, which permits use, sharing, adap-
tation, distribution and reproduction in any medium or format, as long as
you give appropriate credit to the original author(s) and the source, pro-
vide a link to the Creative Commons licence, and indicate if changes were
made. The images or other third party material in this article are included
in the article's CreativeCommons licence, unless indicated otherwise in a
credit line to the material. If material is not included in the article's
Creative Commons licence and your intended use is not permitted by
statutory regulation or exceeds the permitted use, you will need to obtain
permission directly from the copyright holder. To view a copy of this
licence, visit http://creativecommons.org/licenses/by/4.0/.
1506 Mycol Progress (2020) 19:1495–1509

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