Entoloma ravinense – an endangered species of fungus

By Pam Catcheside & David Catcheside
Email: Pam Catcheside pam.catcheside[at]sa.gov.au
First published: Catcheside PS, Catcheside DEA (2021). Entoloma ravinense – an endangered species of fungus. The South Australian Naturalist. 94: 168-172.

Figure 1. Fruit bodies of Entoloma ravinense. Photo: David Catcheside

INTRODUCTION
Mycologists, people who study fungi, get very excited when they come across rare or interesting species or groups of species. One such is a group of small, almost stemless gilled fungi, in the subgenus Claudopus.

We have been surveying the fungi in the parks of Kangaroo Island, especially at the western end of the island in Flinders Chase National Park (FCNP) and in the Ravine des Casoars Wilderness Protection Area (RdCWPA) since 2002. We have scientific collection permits and all collections are accessioned into the State Herbarium of South Australia (AD). In 2010, when collecting fungi in the RdCWPA, we found a few fruit bodies of a pretty white, fan-shaped fungus with a short, lateral stem (Fig. 1). It was growing on the underside of soft, rotten shed bark of sugar gum Eucalyptus cladocalyx F. Muell.. The fungus is almost indistinguishable macroscopically from a common little fungus, Crepidotus variabilis (Pers.) P. Kumm. (Fig. 2), but there was something about the pinkish colour of the gills (Fig. 3) that made me wonder if this was a Claudopus rather than a Crepidotus. Species of Crepidotus produce a brown spore print whilst that of species of Claudopus is pink.

Figure 2: Fruit bodies of Crepidotus variabilis. Photo: David Catcheside
Figure 3: Entoloma ravinense. Underside of cap showing gills. Photo: David Catcheside

 

 

 

 

 

 

 


IDENTIFICATION

When we got back to the lab at the Baudin Centre in Flinders Chase National Park (FCNP), now sadly completely razed to the ground by the 2020 bushfires, I checked the spores under the microscope and, sure enough, they were the angular spores of Claudopus (Fig. 4), not the almost spherical spores of the Crepidotus.

Figure 4: Basidiospores of Entoloma ravinense. Scale Bar 10 microns. Photo: Pam Catcheside

We should not be calling the fungus a Claudopus as molecular work shows this genus is more properly regarded as part of the large genus Entoloma of approximately 1000 species (Kirk et al., 2008). Before molecular tools for determining relationships between organisms were available, morphological characters were used to identify and classify fungi. Based on morphology, species of Claudopus, with their lateral stems and fan-shaped cups, were regarded as distinct from Entolomas that have a traditional mushroom shape and a central stem. However, DNA sequence data show that species of Claudopus nest in the phylogeny (evolutionary tree) of Entolomas and so they are now incorporated into the larger genus.

The fan-shaped Entolomas of the subgenus Claudopus are often overlooked, in part due to their habitat often being in cryptic places and their usually small size. Most are saprotrophic, growing on dead, often rotten wood and bark, on debris of grasses and sedges, on the ground or on mosses but occasionally parasitic on other fungi such as species of Cantharellus. Claudopus species are considered to be rare, with about 25 currently recognised.

So, we had found and collected a rare species. We were helped by Helen Vonow, Collection Manager at the State Herbarium who, in the last ten years, has often accompanied us on our surveys of Kangaroo Island. Helen has a remarkable ability to hunt down whatever species we are seeking and it has often been Helen who makes the first discovery.

In 2010 twelve fruit bodies were found. They were scattered over a piece of bark measuring approximately 15 x 10 cm. In spite of thorough searches, it was not seen in 2011 and 2013 but three fruit bodies were found in 2014, again on a small piece of bark. Seven fruit bodies were found and collected in 2015, three in 2016 and eight in 2017. In all cases, they were growing on the undersides of shed, rotten bark of Eucalyptus cladocalyx and at the same location in the Ravine des Casoars. We had been concerned that this may be the only habitat for this rare fungus but were delighted to find it, again on shed sugar gum bark, at the Rocky River Walking Trail in Flinders Chase National Park. Collections are made carefully to ensure that sufficient fungal tissue, mycelium and spores, are left at the site to enable further growth and fruiting.

NEW SPECIES
The fungus was different from other white, laterally attached species of Entoloma in having larger fruit bodies, closer gills and larger basidia (microscopic structures on the surface of gills on which spores are produced). After intensive descriptions of macroscopic and microscopic characters and molecular work to determine that this was, in fact, a previously undescribed species, the little fungus was described formally (Catcheside et al. 2016) and given the name Entoloma ravinense P.S.Catches., Vonow & D.E.A.Catches., from its first location in the Ravine des Casoars.

To our delight, not only was Entoloma ravinense a new species in a rare group of fungi, the type specimen became the millionth specimen to be accessioned into the State Herbarium (AD), thus a significant member of the herbarium’s collections.

In 2019, Tom May of the National Herbarium of Victoria called for nominations of fungi to be assessed for inclusion in the rare, endangered and threatened species lists produced by the International Union for the Conservation of Nature (IUCN). Entoloma ravinense was considered an appropriate candidate for inclusion. After an exhaustive assessment procedure conducted firstly in Melbourne and later by the IUCN panel, this species was assessed as Endangered (En) (Catcheside & May 2019).

Entoloma ravinense is a saprotrophic fungus, seemingly specific to the bark of Eucalyptus cladocalyx since we have not found it on the bark of other eucalypts. It also seems specific to the underside of often well-rotted shed bark. In spite of extensive and thorough surveys beginning in 2002, the fungus was not found until after the 2007 fires. It is possible that the thick bark, shed after the intense bushfires of December in that year, provides the substrate required for the growth of Entoloma ravinense and it only begins to form fruiting bodies after about three years. So it is possible that a suitable fire regime is necessary for the survival of this rare fungus.

The severe and extensive bushfires in the summer of 2019-2020 burnt through both locations where the fungus has been found, causing destruction and tree death. On a visit to both locations in July 2020, we found considerable quantities of fresh, shed bark of E. cladocalyx. Based on the gap before fruiting was seen after the 2007 fire, we are not expecting to find the fungus fruiting before 2022. However, it is possible that the spore and mycelial bank within the environment has been completely destroyed. In which case, this little fungus, found in 2010 and described in 2016, may be extinct.

Since the DNA ‘fingerprint’ of Entoloma ravinense is known, given appropriate funding it is feasible to probe soil and other substrates to hunt for evidence of its survival. Eucalyptus cladocalyx is endemic to South Australia and is found naturally in three distinct populations, in the Flinders Ranges, Eyre Peninsula and on Kangaroo Island. However, it has been planted widely and has even become naturalised in other countries so the substrate for Entoloma ravinense is widely distributed.

It is to be hoped that the spores and mycelium of this little fungus survived the intense Kangaroo Island fires last summer and that its fruit bodies will reappear in due time but if not, there is still hope it just might survive elsewhere. Specialist decomposers and recyclers such as this may not have the same attraction of iconic animal and plant species. Nevertheless, they merit recognition for the important roles they play in the biosphere and, in this case, recycling the bark of one of our iconic trees.

Specific references
Catcheside PS, Vonow HP, Catcheside DEA (2016). Entoloma ravinense (Agaricales, Basidiomycota), a new species from South Australia. Journal of the Adelaide Botanic Gardens 29: 41-51. https://archive.org/details/journal-adelaide-botanic-garden-29-041-051
Catcheside P, May T (2019). Entoloma ravinense. The IUCN Red List of Threatened Species 2019: .T154843479A154843580. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T154843479A154843580.en.
Kirk PM, Cannon PF, Minter DW & Stalpers JA (2008). Ainsworth & Bisby’s Dictionary of the Fungi, 10th edn.