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A new species of Psathyrella (Psathyrellaceae, Agaricales) from Italy
expand article infoGiovanni Sicoli, Nicodemo G. Passalacqua, Antonio B. De Giuseppe, Anna Maria Palermo, Giuseppe Pellegrino
‡ The University of Calabria, Cosenza, Italy
Open Access

Abstract

Sporophores of a new Psathyrella species have been reported for the first time as growing at the base of Cladium mariscus culms in the Botanical Garden of the University of Calabria, Rende, Cosenza, southern Italy. The fungus was initially identified as P. thujina (= P. almerensis) by means of both ecology and macro- and microscopic characteristics of the basidiomes, then referred to P. cladii-marisci sp. nov. after extraction, amplification, purification and analysis of the rDNA ITS region. We came to this conclusion after comparing our specimen with the descriptions of the taxa available in the literature for the genus Psathyrella.

Keywords

Agaricomycetes, Basidiomycota, Fen-sedge, Marshes, southern Italy, Taxonomy

Introduction

Within the cosmopolitan fungal genus Psathyrella (Fr.) Quél. (Agaricales, Psathyrellaceae), about one hundred species have traditionally been recognised in Europe, almost all saprotrophs and found in many and diverse environments. Either terrestrial or lignicolous, they grow mainly on organic debris from various origins, such as dung, post-fire locations and dead stems of larger herbaceous plants (Vesterholt and Knudsen 1992). Psathyrella basidiomes are pileate, stipitated and exannulate or, at most, with a fugacious ring and the hymenophore is gilled, pale pink when young, turning brown with age due to a dark spore print. Moreover, they have, as the etymology indicates, a very fragile and ephemeral consistency. Despite these common macroscopic characters of the basidiomes, a recent phylogenetic analysis revealed the extremely complex origin of this genus, recognising species as belonging to a Psathyrella sensu stricto group or to P. sensu lato complex, the former including 19 clades and the latter involving eight genera (Coprinellus, Kauffmania, Cystoagaricus, Typhrasa, Lacrymaria, Homophron, Coprinopsis, Parasola), thus consistently widening the list of such “psathyrelloid” basidiomycetes (Örstadius et al. 2015).

During an investigation on the mycoflora of the Botanical Garden at the University of Calabria (Rende, Cosenza, Italy), basidiomes of an apparently “psathyrelloid” fungus were detected at the base of a fen-sedge [Cladium mariscus (L.) Pohl (Cyperaceae)], a cosmopolitan-distributed plant species (Lansdown et al. 2018) occurring in marshy places of most Italian regions (Bartolucci et al. 2018), but rarely in southern Italy.

Based on records reported by Örstadius et al. (2015), nine clades of Psathyrella s.s. include species associated with moist soils and marshy places: “spadiceogrisea” (four species), “fibrillosa”, “noli-tangere” and “prona” (two species each), “candolleana”, “cystopsathyra”, “lutensis”, “obtusata” and “pygmaea” (one species each). Nevertheless, only three species have been found to be growing on sticks or on remnants of hygrophilous plants: P. lutensis (Romagn.) Bon, as a monospecific “lutensis” clade, P. thujina A.H. Sm. (=P. almerensis Kits van Wav.) in the “spadiceogrisea” clade and P. typhae (Kalchbr.) A. Pearson & Dennis in the “candolleana” clade.

The aim of this work was therefore to identify our basidiomes by using both morpho-ecological and biomolecular tools. This was highly encouraged by the habitat peculiarity and the close relationship with a plant species with which no species of Psathyrellaceae had ever been found associated.

Materials and methods

Eight basidiomes of the above “psathyrelloid” fungus were observed and collected on 10 April 2018, as gregarious all around and at the base of Cladium mariscus cut culms (Fig. 1). In 2012, that plant had been removed, together with the whole clump of mud attached to its roots, from a natural marsh named Lago dell’Aquila (Laureana di Borrello, Reggio Calabria, southern Italy) and transplanted to the Botanical Garden at the corner of a 90 × 37 cm-wide and 30 cm-deep concrete tank, which had permanently been kept full to the brim with water. Since then, some leaves of water lily (Nymphaea alba L.) have been introduced to float on the water surface inside the tank and the mud mass has been increasing, while the C. mariscus plant has been expanding and producing new culms that are cut every year.

Figure 1. 

A tuft of Cladium mariscus planted in a tank at the Botanical Garden of the University of Calabria, southern Italy (A), and first-sight features of Psathyrella basidiomes at the base and in-between of remnants of excised culms of the plant (B).

Morphology

The basidiomes were first macroscopically examined for features, colours, sizes, hymenophore shape, pileus and stipe ornamentations, smell and taste. Then, the structures of the basidiome were microscopically inspected for cheilo- and pleurocystidia occurrence and features, presence of clamp connections, basidia and spore features. These observations were carried out under a light microscope (Axioplan 2 Imaging Microscope, Carl Zeiss, Germany) at 400 and 1,000 magnifications on fragments of pileipellis and gills placed on slides in 10% NH4OH. The results were compared with those published in the morphological keys for the Psathyrella species and, more specifically, with those species reported as the closest, according to morphology and ecological site conditions, i.e. P. thujina, P. typhae and P. lutensis (Kits van Waveren 1985, Vesterholt and Knudsen 1992, Christan et al. 2017, Henrici 2017).

DNA Extraction, Amplification and Sequencing

One of the basidiomes was dehydrated at room temperature and destroyed for molecular analysis: DNA extraction, amplification, purification and sequencing of the nuc rDNA internal transcribed spacer region (ITS). DNA extraction was implemented by using CTAB protocol (Doyle and Doyle 1987) and the ITS region was amplified using the primer combination ITS1F/ITS4 (White et al. 1990). The polymerase chain reaction (PCR) was performed in a 25-µl reaction volume containing 1.0 µl DNA, 2.5 µl 10 × 5-Prime–MasterMix Buffer (Thermo Fischer Scientific, Waltham, Massachusetts, USA) and 1.25 µl of each primer (10 µM/µl). The PCR was carried out according to the following amplification programme: 3 min initial denaturation at 94 °C, 35 cycles (30 s denaturation at 94 °C, 1 min annealing at 55 °C, 45 s extension at 72 °C) and a 10 min final extension at 72 °C. This programme was carried out in a T1000 Thermocycler (Biometra, Goettingen, Germany). The PCR products were purified using a QIAquick PCR purification kit (Qiagen Inc., Valencia, California, USA). Sequencing was performed by means of a Bigdye terminator cycle sequencing kit (Applied Biosystems, Foster City, California, USA). The sequencing reaction was run by BMR Genomics (Padua, Italy) on a 96-capillaries ABI 3730XL DNA Sequencer.

Forward and reverse DNA fragment electropherograms were checked by means of the CHROMAS 2.6.5 software (technelysium.com.au) for a complete reconstruction of the ITS1, ITS2 and 5.8 gene fragments. Ambiguous regions at the start and the end of the alignment were deleted and gaps were manually adjusted to optimise the alignment. The sequence generated for this study is deposited in GenBank with the code MK080112.

Alignment and Phylogenetic Analysis

Consensus sequences were generated from both forward and reverse primer reads in the BioEdit sequence alignment editor, version 7.2.5 (Hall 1999), then homology searches were performed at the National Centre for Biotechnology Information (NCBI) Web site using BLAST. This sequence was then compared with those of the Psathyrella species deposited in GenBank on which the phylogenetic analysis had recently been performed (Padamsee et al. 2008, Battistin et al. 2014, Örstadius et al. 2015, Yan and Bau 2018). A total of 45 ITS sequences, including three Coprinellus spp. (Table 2) were aligned using MAFFT with the L-INS-i option (Katoh et al. 2017). The aligned ITS dataset consisted of 702 nucleotide sites (including gaps). FASTA alignments from MAFFT were loaded in IQ-TREE 1.5.6 (Nguyen et al. 2014) to perform Maximum Likelihood Analysis. Clade robustness was assessed using a bootstrap (BT) analysis with 1,000 replicates (Felsenstein 1985). Phylogenetic trees were visualised using the FigTree v1.3.1 (Rambaut 2009).

Results

Morphology

The macro- and micro-morphological features of the basidiomes collected at the base of the fen-sedge plant in the Botanical Garden are shown in Figures 2, 3. At first sight, by observing the macro-level characters, i.e. the small-medium size, the extreme fragility at handling and the brown-blackish spore print, the basidiomes were easily assigned to the Psathyrella genus (Vesterholt and Knudsen 1992). Secondly, the occurrence of sphaeropedunculate and clavate cells along the gill edge and the utriform shape of some cheilo and pleurocystidia seemed to direct them to the Section Spadiceogriseae Kits van Wav., subsection Spadiceogriseae (Romagn.) ex Kits van Wav. (Kits van Waveren 1985).

Figure 2. 

Macro-morphological characteristics of the Psathyrella basidiomes: scales of velar origin on pilei tops and margins, and beige-coloured gills (A); cylindrical, white and exannulate stems under a lateral profile (B); colour-shading of a cap hygrophany and fibrillose details of velar-originated scales (C); gills turning brown-purplish with spore maturation and a fibrillose surface of a stem base (D); a pruinose stem apex bearing a mature hymenophore with white gill edge lines (E).

Figure 3. 

Micro-morphological characteristics of the Psathyrella mycelium: clavate and sphaeropedunculate (A), and cylindric (B, C) cells at a gill edge; differently clavate (D, E) and utriform (F) cheilocystidia; variously utriform-shaped pleurocystidia (G, H, I); a fibulate hypha (J); a 4-spored basidium (K); basidiospores (L).

If we compare the morphological features of our specimens with those belonging to the closest Psathyrella species, a number of differences emerge (Table 1). Our specimens appeared to be more similar to P. thujina (Henrici, 2017), previously described as P. almerensis (Kits van Waveren 1985, Vesterholt and Knudsen 1992), except for the pileus diameter reaching 3.5 cm in our specimens, but never exceeding 2.5 cm in this species. Furthermore, our Psathyrella revealed versiform-shaped cheilocystidia, while those reported for P. thujina are only utriform. P. typhae was also divergent for the pileus diameter, not exceeding 2.5 cm, but even for pileus and stipe colours and for lacking pleurocystidia. On the other hand, the mucoid deposits, characterising the pleurocystidioid cheilocystidia of P. lutensis, were absent in our specimens. In addition, the spore length range was wider in our specimens than in P. thujina and P. lutensis and all the closest three species, which showed larger spores on average.

Main differences between our Psathyrella sp. and the closest species, according to the morphological characteristics of basidiomes and mycelium, and ecology. (Differences from our specimen are in bold characters).

Morpho-ecological characteristics Psathyrella sp. P. thujina P. typhae P. lutensis
Pileus diameter (cm) 3.5 2.5 2.5 4.0
Pileus colour Hazelnut brown, then beige brown Warm brown, then beige brown Pinkish-ochre brown, then pale flesh brown Dark reddish brown, then very pale brown
Stem colour White with a pruinose apex White with a pruinose apex Whitish to pale brown White with a pruinose apex, brownish base
Spore size (µm) 7.2–11.8 x 4.3–6.0 9.0–11.5 x 4.5–6.5 7.5–11.5(12.0) x 5.5–8.0 9.0–10.0 x 4.5–5.5
Cheilocystidia Versiform, chiefly utriform Utriform Versiform, chiefly utriform Versiform, chiefly utriform
Pleurocystidia Utriform Utriform Absent Versiform, chiefly utriform to ventricose
Mucoid deposits on cystidia NO NO NO YES
Habitat Marshes, on cut culms of Cladium Marshes, on cut culms of Typha, Phragmites, Cirsium, Epilobium Marshes, on cut culms of Typha, Epilobium, Scirpus, Phragmites, Rumex, Iris Deciduous forests, on sticks in mud
Seasonal occurrence Spring Autumn to winter Summer Summer to autumn

As for ecology, the plant genus Cladium Browne has never been reported as a substrate to any other Psathyrella, although P. thujina and P. typhae are commonly found on the remnants of ecologically similar plants (Kits van Waveren 1985, Vesterholt and Knudsen 1992, Örstadius et al. 2015, Henrici 2017). Furthermore, the genus Cladium was not mentioned in the unique Italian report of P. thujina, which was found “in open sites, close to any hygrophilous plants” (Voto 2016), in accordance with Henrici (2017) who refers this species to reed-beds and generic damp marshy habitats. Finally, our specimen was collected in the spring, whereas the above three other Psathyrella species seem to occur in other seasons.

DNA Analysis

The obtained nrDNA sequence was 702 bp long. By comparing it with those published in GenBank, we obtained a data matrix composed of 44 taxa and 710 characters, 276 gap-free sites and 240 conserved sites. The highest homology (99%) was observed with P. candolleana (Fr.) Maire, which was confirmed by the phylogenetic analysis (Fig. 4). Indeed, the phylogenetic tree shows that our specimen falls into the “candolleana” clade, such a heterogeneous group, including taxa from different morphology, ecology and geographic provenance and, amongst them, the above-cited P. typhae (Battistin et al. 2014, Örstadius et al. 2015, Yan and Bau 2018).

Figure 4. 

One of the most parsimonius trees from the phylogenetic analysis of Psathyrella spp. based on nrDNA sequence data. Bootstrap values are shown above branches based on 1,000 replicates (values below 50 are not shown).

Species used for the phylogenetic analyses including GenBank Accession Numbers and published references.

Species GenBank accession No. Reference
Psathyrella abieticola KC992891 Örstadius et al. 2015
P. almerensis KC992874 Örstadius et al. 2015
P. almerensis KC992873 Örstadius et al. 2015
P. ammophila KC992872 Örstadius et al. 2015
P. candolleana AB306311 Ogura-Tsujita and Yukawa 2008
P. candolleana DQ389720 Larsson and Örstadius 2008
P. candolleana MG734719 Yan and Bau 2018
P. candolleana MG734720 Yan and Bau 2018
P. cladii-marisci MK080112 This study
P. conferta KC992890 Örstadius et al. 2015
P. conica MG734713 Yan and Bau 2018
P. flexispora MF966494 Heykoop and Moreno 2002
P. fusca MF966503 Heykoop and Moreno 2002
P. impexa KC992900 Örstadius et al. 2015
P. kellermanii KC992920 Örstadius et al. 2015
P. luteopallida MG734736 Yan and Bau 2018
P. lutensis MG734748 Yan and Bau 2018
P. lutensis DQ389685 Larsson and Örstadius 2008
P. lutulenta KC992875 Örstadius et al. 2015
P. madida KC992932 Örstadius et al. 2015
P. parva KC992912 Örstadius et al. 2015
P. prona KJ939634 Larsson and Örstadius 2008
P. pseudogracilis KC992853 Örstadius et al. 2015
P. purpureobadia NR_119670 Larsson and Örstadius 2008
P. romagnesii DQ389716 Larsson and Örstadius 2008
P. saponacea MH155965 Yan and Bau 2018
P. senex MG734732 Yan and Bau 2018
P. singeri MG734718 Yan and Bau 2018
P. squamosa KC992939 Örstadius et al. 2015
P. squamosa MG367206 Yan and Bau 2018
P. subsingeri MG734714 Yan and Bau 2018
P. sulcatotuberculosa KJ138423 Battistin et al. 2014
P. tenera FJ899635 Frank et al. 2010
P. tenuicula DQ389706 Larsson and Örstadius 2008
P. thujina KC992873 Örstadius et al. 2015
P. thujina KC992874 Örstadius et al. 2015
P. thujina KY680791 Örstadius et al. 2015
P. thujina KY680792 Örstadius et al. 2015
P. trinitatensis KC992882 Örstadius et al. 2015
P. tuberculata MH497604 Yan and Bau 2018
P. typhae DQ389721 Larsson and Örstadius 2008
Coprinellus heterothrix FM878018 Nagy et al. 2011
C. impatiens FM163177 Nagy et al. 2011
C. silvaticus KC992943 Örstadius et al. 2015

Discussion and conclusions

Based on results from both morphological and molecular analysis, our collection cannot be assigned to a known species. According to morphology, our Psathyrella should be closer to P. thujina (Section Spadiceogriseae). By contrast, the DNA ITS sequence would undoubtedly include it in the “candolleana” clade, where each species showed up to a 99% ITS sequence similarity with our sample. The most widespread and known species in this clade, P. candolleana and P. leucotephra (Berk. & Broome) P.D. Orton, both commonly occurring in Europe, too, are however morphologically very different from our specimen, by forming large pilei (diameter up to 8.0 cm) and lacking pleurocystidia; furthermore, the latter frequently even shows a torn annulus in the upper part of the stem, which we did not observe in our Psathyrella (Kits van Waveren 1985, Vesterholt and Knudsen 1992, Consiglio 2005). The “candolleana” clade encompasses two more European species according to two recent phylogenetic analyses (Nagy et al. 2011, Battistin et al. 2014): P. sulcatotuberculosa (J. Favre) Einhell., previously regarded as a variety of P. typhae (Kits van Waveren 1985), which mainly differs from our Psathyrella and from P. typhae itself with a partially-sulcate and -tuberculate pileus surface, and P. badiophylla (Romagn.) Bon which forms spores normally exceeding 10–11 µm in length (Kits van Waveren 1985, Vesterholt and Knudsen 1992); in addition, both also lack pleurocystidia, which was considered to be such a morphologically relevant character to induce the establishment of the Section Spintrigerae within the subgenus Psathyra (Fr.) Sing. ex Kits van Wav. (Kits van Waveren 1985). Moreover, except for P. typhae, which is the only Psathyrella ecologically comparable to our collection, all the above species are reported to grow in diverse site conditions, i.e. close to stumps of trees or on branches, on moist ground, in grass, on mossy woods or on various other vegetable matter (Kits van Waveren 1985, Vesterholt and Knudsen 1992). Finally, as far as we know, other species in the “candolleana” clade are even geographically more distant, each colonising a different kind of organic debris (Padamsee et al. 2008, Örstadius et al. 2015, Yan and Bau 2018).

Therefore, within this framework, the placement of our fungus into the “candolleana” clade, together with other species showing strong differences for geographic and ecologic reasons, should not prevent the recognition of a new Psathyrella species.

Anyhow, more and more scientific contributions are remarking that the genetic analysis of a fungus aiming at taxonomic purposes can alone generate artefacts, i.e. “false positive” or “chimeras”, especially when such analysis is implemented by using a unique gene (Thines et al. 2018, Lücking et al. 2018). A polyphasic approach, i.e. based on the combination and integration of all the available informative data (Colwell 1970), is becoming more and more desirable for taxonomic research in mycology, whereas the ITS rDNA region is still considered as the universal genetic marker for fungi (Schoch et al. 2012).

On the basis of the outcomes deriving from the morphologic, ecologic and biomolecular characteristics which we have identified in this note, we are therefore inclined to establish a new species of Psathyrella.

Taxonomy

Psathyrella cladii-marisci Sicoli, NG Passal., De Giuseppe, Palermo & Pellegrino, sp. nov.

Figs 1, 2, 3

Etymology

The specific epithet derives from Cladium mariscus, the name of the plant where it was first detected.

Diagnosis

Similar to P. thujina from which it differs by showing a larger pileus (about 40% larger), a wider range of spore length, versiform cheilocystidia and basidiomes occurring in spring.

Holotype

Italy. Calabria, Cosenza, Rende, Orto Botanico Università della Calabria. 39°21'25.05"N, 16°13'44.57"E, 220 m a.s.l., marsh at the base of cut culms of a Cladium mariscus (L.) Pohl plant, transplanted from Lago dell’Aquila (Laureana di Borrello, Reggio Calabria, southern Italy) at the corner of a concrete tank maintained full of water, 10 April 2018, Antonio Biagio De Giuseppe & Giovanni Sicoli (CLU F302).

Description

Habit psathyrelloid. Pileus up to 3.5 cm diam., conical-convex when young, hemispheric to applanate at maturity, with a deeply striate margin, hazelnut in colour, turning to pale beige when dry. Pileipellis with evident concentric arachnoid fibrils of velar origin, whitish and easily removable, often exceeding the cuticle margin. Lamellae distant, ventricose, adnate, intermingled with numerous lamellulae, initially pale pink, then intensely brown-purplish. Lamella edge whitish with numerous sphaeropedunculate cells. Stipe, very fragile, cylindrical, white, exannulate with a diffuse fibrillosity especially on the basal surface, apical surface pruinose. Basidiospores 7.2–11.8 × 4.3–6.0 µm (n = 100), ellipsoid to ovoid-ellipsoid, with a thick and smooth wall, adaxially flattened with a central 2µm-wide germ pore and a distinct hilar appendix. Spore-print dark brown. Basidia clavate, 4-spored. Cheilocystidia versiform, often utriform, seldom cylindrical to clavate. Pleurocystidia utriform-shaped. Mycelium septate and clamped. Context with apparently no smell, taste mild.

Habit, habitat and distribution

In small groups (gregarious), on the culm remnants of Cladium mariscus. So far, known only from the type locality.

Conclusions

This probably rare and, apparently, never before detected species could occur more commonly if further surveys confirmed a sort of preference for C. mariscus as a growing substrate for the fungus. This plant was observed all over Italy (Bartolucci et al. 2018), although becoming more and more scattered due to the progressive surface reduction of its natural growing environment, i.e. marshes and wet sites quite close to the sea at mid-low altitudes. These sites have been long subjected to draining and other forms of anthropogenic land uses. Since human activities have been causing a deep influence and restriction on density and distribution of the spontaneous flora, including C. mariscus, the gradual depletion of plant biodiversity in such sites could also result in negative effects on fungal diversity, thus rendering even more scarce the occurrence of basidiomes of such taxa as P. cladii-marisci in Italy.

Acknowledgements

We are very grateful to Pasquale A. Cicirelli and Nicola Fico for their precious advice in the digital image processing.

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