Sinohygrocybe gen. nov., typified by S. tomentosipes sp. nov., is described upon morphological and molecular evidence. The new genus is characterised by its sinuate to subdecurrent or short deccurent, usually furcate and interveined and relatively distant lamellae, dry and whitish tomentose stipe, thin-walled ellipsoid to oviod, non-constricted basidiospores and particularly elongated basidia and a ratio of basidiospore to basidium length of >5 to 8; it is close to genera Chromosera and Gloioxanthomyces of the tribe Chromosereae, but morphologically differs from Chromosera in less umbilicate basidiomata, tomentose stipe and usually longer basidia and differs from Gloioxanthomyces in more robust basidioma and less glutinous pileus and/or stipe surface. Phylogenetic analyses, with ITS-LSU-RPB2 data, also indicate that Sinohygrocybe forms a very distinct and independent clade at the generic level. In addition, a Chinese new record G. nitidus is described here.

East Asia, new record species, new taxa, phylogeny overview

Hygrophoraceae Lotsy (Hymenomycetes, Basidiomycota) is a large family in Agaricales, including 26 genera and over 600 species (Lodge et al. 2014). In a six-gene phylogenetic tree of Agaricales, Hygrophoraceae, Pterulaceae Corner, Typhulaceae Jülich and some small groups formed a Hygrophoroid clade, which is one of the six largest clades in Agaricales (Matheny et al. 2006); and in a genome based mushroom tree of life, Hygrophoraceae and Clavariaceae Chevall. are representative families of the suborder Hygrophorineae Aime, Dentinger & Gaya, which is one of the seven suborders of the Agaricales (Dentinger et al. 2016). Traditionally, the family Hygrophoraceae referred to a group of agaricoid, waxy-gilled and white-spored mushrooms; and a majority of the members are classified in the type genus Hygrophorus Fr. and genus Hygrocybe (Fr.) P. Kumm. Morphological characters of the Hygrophoraceae taxa are relatively simple (usually without annulus or volva and a cystidiate) amongst the agaric fungi and their basidioma colours are often very susceptible to the environmental conditions and developmental stages, making their classification and identification difficult, so it is often challenging to make correct identification and taxonomy of them just according to morphological recognition (Young 2005). Modern molecular techniques have been revolutionising the taxonomy and phylogeny of Hygrophoraceae.

Lodge et al. (2014) had conducted the most comprehensive molecular phylogenetic study on the family until now, therefore their systematic viewpoint on Hygrophoraceae is adopted in this paper. According to their study, the family could be divided into four groups at subfamily level, i.e. subfamily Hygrophoroideae E. Larss., Lodge, Vizzini, Norvell & S.A. Redhead, Hygrocyboideae Padamsee & Lodge, Lichenomphalioideae Lücking & Redhead and Cuphophylloid grade. The subfamily Hygrocyboideae could be divided into three tribes, i.e. tribe Chromosereae, Humidicuteae and Hygrocybeae; and the tribe Chromosereae included two sister genera, Chromosera Redhead, Ammirati & Norvell and Gloioxanthomyces Lodge, Vizzini, Ercole & Boertm.

Chromosera, the type genus of the tribe Chromosereae, was erected to accommodate Omphalina cyanophylla (Fr.) Quél. which was originally described from Sweden and combined as C. cyanophylla (Fr.) Redhead, Ammirati & Norvell (Redhead et al. 1995, 2012). Now, another four species, formerly placed in Hygrocybe or Hygrophorus, are also classified into Chromosera, i.e. C. citrinopallida (A.H. Sm. & Hesler) Vizzini & Ercole originally described from USA, C. lilacina (P. Karst.) Vizzini & Ercole originally described from the northern Fennoscandia, C. viola (J. Geesink & Bas) Vizzini & Ercole originally described from Belgium and C. xanthochroa (P.D. Orton) Vizzini & Ercole originally described from Scotland (Lodge et al. 2014).

Gloioxanthomyces is a small genus with only two known species, the type species G. vitellinus (Fr.) Lodge, Vizzini, Ercole & Boertm. originally described from Europe and G. nitidus (Berk. & M.A. Curtis) Lodge, Vizzini, Ercole & Boertm. from North America (Crous et al. 2004, Lodge et al. 2014). Before the recognition of Gloioxanthomyces, those two species were usually placed in the genus Hygrocybe as H. vitellina (Fr.) P. Karst and H. nitida (Berk. & M.A. Curtis) Murrill, respectively. Morphologically, the main differences between the two species were in their basidiospore sizes: G. nitidus had ellipsoid to oblong basidiospores, measuring 7–10 × 5–6 μm with Q = 1.3–1.8; while G. vitellinus had subglobose basidiospores, measuring 6.5–8.5 × 5–7 μm with Q=1.1–1.6 (Boertmann 1990). Since their differences were limited, the two taxa seemed to be conspecific (Boertmann 2011). However, according to the phylogenetic analyses with ITS data by Boertmann (2012), the European collections clearly clustered together as the G. vitellinus species clade, while the North American materials independently formed another group as the G. nitidus species clade, thus they could actually be sharply defined as two separated sister species.

During the studies on the Chinese Hygrophoraceae in recent years, some collections morphologically corresponding to tribe Chromosereae were collected. Comprehensive observation and analyses revealed some interesting findings, which can contribute to the taxonomic knowledge of the tribe. In this paper, we aim to: 1) formally describe a new genus of tribe Chromosereae from East Asia based upon morphological and molecular analyses and present a Chinese new record of Gloioxanthomyces nitidus; 2) reconstruct the phylogeny of the family Hygrophoraceae using 3 gene regions, i.e. the internal transcribed spacer region (ITS), the large subunit nuclear ribosomal RNA region (nrLSU) and the nuclear RPB2 6F to 7.1R region (RPB2). Detailed studies were therefore conducted and the results are presented as follows.

Phylogenetically, the distinction of the three subfamilies (Lodge et al. 2014) within Hygrophoraceae has very convincing support in the multi-locus tree of this study (Fig. 1). In addition, the establishment of the three well-defined monophyletic tribes in subfamily Hygrocyboideae is supported in this phylogenetic frame where the tribe Hygrocybeae with 73% support values and the tribe Humidicuteae with low support value are sister clades, while the tribe Chromosereae with 76% support values is located at their base. However, the cuphophylloid grade appears not to be monophyletic, thus more studies are still needed to understand the phylogenetic positions of Ampulloclitocybe, Cantharocybe H.E. Bigelow & A.H. Sm. and Cuphophyllus (Donk) Bon.

In the multi-gene analyses, Sinohygrocybe is placed together with two other genera in Chromoserae. Chromosera and Gloioxanthomyces are sister genera under the monophyletic tribe Chromosereae, while Sinohygrocybe is an independent generic lineage; and the distances between Sinohygrocybe and Chromosera or Gloioxanthomyces are further than the distance between Chromosera and Gloioxanthomyces. Such results are confirmed in the ITS phylogenetic tree (Fig. 2). According to the Blastn results, the ITS and LSU sequence identities of the new species to the known taxa are not more than 76% and 96%, respectively, with the Chromosera and Gloioxanthomyces sequences in GenBank. Thus, it is clear the new genus is independent of those two existed genera.

Beside the molecular analyses, morphological data also support its recognition within tribe Chromosereae. Sinohygrocybe shares a bright pileus colour and decurrent lamellae with the other genera Chromosera and Gloioxanthomyces (Table 2). However, the genus Chromosera, typified by C. cyanophylla (Fr.) Redhead, Ammirati & Norvell, differs from Sinohygrocybe in having omphaloid basidiomata, ephemeral dextrinoid reactions in the context, ratio of basidiospore to basidium length <5, ephemeral pigment bodies in the pileipellis and lilac pigments sometimes present (Redhead et al. 1995, Candusso 1997, Lodge et al. 2014); while Gloioxanthomyces differs from Sinohygrocybe by having weaker/delicate basidiomata, viscid pileus and stipe surface, gelatinised lamellar edge and cheilocystidia, shorter basidia (Boertmann 1990, 2012) with a length ratio of basidium to basidiospore 4–5. Sinohygrocybe shares some macroscopic characters with Hygrocybe, typified by H. conica, including bright colour of basidiomata and the distant lamellae, but Hygrocybe differs from Sinohygrocybe by having more fragile lamellae, more glabrous stipe (at least at the upper portion), often constricted spores and shorter basidia.

Sinohygrocybe samples were collected in both late summer (August) and winter (November), showing that they likely have a quite long fruiting season. It should be noted, however, that they are more abundant at times with lower temperature and higher humidity. Therefore, their fruiting in summer may occur only at higher altitude (with the elevation above 1500 m).

As to the Chinese new Gloioxanthomyces nitidus record: 1) phylogenetically, the Chinese samples are nested in the Gloioxanthomyces clade as a sister branch to the North American branch (Fig. 2); 2) morphologically, it shares these characters with the North American G. nitidus: deep yellow basidiomata fading to whitish with age, viscid, hygrophanous surface, central concave pileus and decurrent lamellae (Bessette et al. 2012); 3) geographically, G. nitidus and G. vitellinus are distributed in North America and Asia and Europe, respectively, indicating that Gloioxanthomyces is a Holarctic genus. It is assumed that both North American and East Asian G. nitidus were separated from the same ancestor because of geographical isolation, thus they are very similar at present; however, they may continue to diverge, eventually becoming separate species in the future since they live on detached continents.

Sincere acknowledgements are expressed to Dr. Xiao-Lan He and Dr. Egon Horak, Mr. Ye-Wei Xia and members of Dr. Wen-Bo Liao’s laboratory, Dr. Jiang Xu and Mrs. Xin Zhang for their help during the field trips in Gesala, Taoyuandong and Changbai Mountains, respectively; to Dr. Tolger Bau for trying to find some additional samples in HMJAU; to Dr. David Boertmann, Dr. Md. Iqbal Hosen and Dr. Wang-Qiu Deng for their improvements and constructive comments on an earlier version of this paper; to Dr. David Hibbett and the International Exchange Scholarship of the University of Chinese Academy of Sciences for providing an opportunity to the first author to learn molecular data analyses. This study was financed by the Ministry of Science and Technology of China (Nos. 2013FY111500, 2013FY111200), the Science and Technology Program of Guangzhou, China (No. 201607020017), the GDAS’ Special Project of Science and Technology Development (2018GDASCX-0907) and the Science and Technology Project of Guangdong Province (2017A030303050).