The discovery began with a routine but meticulous field campaign. During surveys conducted in 2022 and 2025, the research team collected plant leaves from the Baotianman Nature Reserve in Neixiang County, Henan Province, and samples of rotting wood from Pingtang Wetland Park in Pingtang County, Guizhou Province. Each sample was sealed in a sterile plastic bag, kept on ice, and transported to the laboratory within 24 hours to preserve the living microbial communities. Using specialized isolation techniques, including the ballistoconidia-fall method for leaf samples and established protocols for decaying wood, the team recovered 26 yeast strains in total from the collected materials.

Most of those 26 isolates turned out to belong to eight already-known yeast species, including Bullera alba, Filobasidium magnum, and several members of the genus Symmetrospora. But three strains stood out. Their DNA sequences did not match any formally described species in reference databases, hinting that the team had stumbled upon something genuinely new. Two of the strains, both isolated from leaves of the plant Arisaema heterophyllum in Henan, belonged to one unknown lineage. A third strain, recovered from rotting wood in Guizhou, represented an entirely separate lineage.

To determine whether these strains truly represented new species, the researchers turned to molecular phylogenetics, the standard modern tool for delimiting fungal species. They extracted genomic DNA from each strain and amplified two key genetic markers: the D1/D2 domain of the large subunit ribosomal RNA gene and the internal transcribed spacer (ITS) region. These two regions are the workhorses of yeast taxonomy because they evolve quickly enough to distinguish closely related species while remaining easy to amplify and compare across broad groups of fungi.

The team aligned the new sequences with reference data from GenBank using the software MAFFT, concatenated the two loci into a single dataset, and reconstructed evolutionary relationships using both maximum likelihood and Bayesian inference methods. The resulting phylogenetic trees delivered a clear verdict. The two Henan strains formed a well-supported clade within the genus Tremella, grouping together with an environmental sequence from Japan and a clone from Austria. The Guizhou strain, meanwhile, occupied a distinct position within the genus Pseudotremella, clustering alongside strains previously recovered from Japan, Portugal, and the Tibet Autonomous Region of China.

The degree of genetic divergence was decisive. The Henan strains differed from their closest known relative, Tremella saccharicola, by 14 nucleotide substitutions, roughly 2.3 percent, in the D1/D2 domain, and by 31 nucleotide mismatches, about 6.6 percent, in the ITS region. The Guizhou strain was even more distinct from its nearest neighbor, Pseudotremella allantoinivorans, differing by 23 nucleotide substitutions, approximately 3.8 percent, in the D1/D2 domain and 57 mismatches, nearly 9.8 percent, in the ITS region. In yeast taxonomy, differences of this magnitude are well beyond the thresholds typically used to recognize separate species, leaving little doubt that both lineages deserved formal names.

But DNA alone is not enough to describe a new species. The researchers also conducted extensive phenotypic characterization, following standard methods for yeast taxonomy. They grew the strains on YM agar and observed colony color, texture, and cell morphology under the microscope. Both new species produce ellipsoidal to oval cells that reproduce by polar budding, and neither forms hyphae or pseudohyphae in Dalmau plate cultures on corn meal agar. Neither produced ballistoconidia, the forcibly discharged spores characteristic of some other tremellaceous yeasts, and neither showed any signs of sexual reproduction even after two months of incubation on multiple media designed to induce mating.

The physiological profiles revealed telling differences between the new species and their closest relatives. Tremella arisaematis can be distinguished from T. saccharicola by its ability to assimilate DL-lactate, its failure to use L-rhamnose, myo-inositol, and cadaverine, and its inability to grow at 30 degrees Celsius, a temperature its relative tolerates. Pseudotremella guizhouensis, in contrast, can assimilate inulin but cannot use melibiose or citrate, and it also fails to grow at 30 degrees Celsius, unlike P. allantoinivorans. These metabolic quirks, combined with the genetic data, provide a complete diagnostic package for identifying each new species in the laboratory.

The genus Tremella, first validly described by Persoon in 1794, is the largest genus in the order Tremellales, comprising approximately 90 species as traditionally circumscribed. More than half of these are lichenicolous, meaning they live as parasites or associates on lichens. Molecular phylogenetics has revealed that Tremella as traditionally defined is polyphyletic, meaning it does not descend from a single common ancestor, and the genus is now divided into several major clades that await formal taxonomic resolution. The species in the strict sense belong to the Fuciformis and Mesenterica subclades, which include more than 30 species, over half of which are known to have a yeast state in their life cycle. Members of the genus are dimorphic, alternating between a dikaryotic filamentous stage that forms visible fruiting bodies and a haploid unicellular yeast stage that reproduces by budding.

The genus Pseudotremella, established more recently in 2015, currently comprises eight species distributed across a wide range of habitats, from decaying fungi and tree bark to lichens, leaves, and even animal sources. Only two of the known species, P. moriformis and P. nivalis, have documented sexual morphs that produce tremelloid basidiocarps and basidia on natural substrates. The remaining species, including the newly described P. guizhouensis, are known only from their asexual yeast forms. The discovery of a strain in rotting wood in Guizhou, together with three additional strains from geographically distant regions identified as belonging to the same species, suggests that P. guizhouensis is relatively common and widely distributed, despite having gone unnoticed until now.

Neither of the two new species revealed its sexual stage under laboratory conditions. The researchers attempted to induce mating and fruiting body formation by incubating individual strains and strain pairs on potato dextrose agar, corn meal agar, and V8 agar at 17 degrees Celsius for up to two months, but no basidia or basidiocarps appeared. This is not unusual for tremellaceous yeasts, as many species require compatible mating partners and specific environmental cues to complete their life cycles. The team notes that future experiments pairing compatible strains under appropriate conditions may eventually reveal the sexual morphs of these organisms, as has been accomplished for other species such as Tremella yokohamensis.

The broader significance of the discovery lies in what it says about the state of fungal biodiversity knowledge. The researchers emphasize that the species diversity of both Tremella and Pseudotremella remains underexplored, with additional undescribed taxa likely awaiting discovery in similar habitats. The fact that two new species emerged from a modest survey of just 26 yeast isolates from two Chinese provinces suggests that systematic sampling of leaves, decaying wood, and other plant-associated substrates in understudied regions could yield many more surprises. As molecular tools become faster and cheaper, the hidden fungal diversity of the world’s forests, wetlands, and nature reserves is steadily coming into focus, one species at a time.

Subject of Research: Taxonomic description of two novel basidiomycetous yeast species in the genera Tremella and Pseudotremella isolated from plant materials in China

Article Title: Two new species of Tremella arisaematis ( Tremellaceae ) and Pseudotremella guizhouensis ( Bulleraceae ) from China

Article References: Two new species of Tremella arisaematis ( Tremellaceae ) and Pseudotremella guizhouensis ( Bulleraceae ) from China. (n.d.). https://doi.org/10.3897/mycokeys.141.205833

Image Credits: AI Generated

DOI: 10.3897/mycokeys.141.205833

Keywords: Tremella, Pseudotremella, yeast taxonomy, basidiomycetous yeasts, fungal diversity, phylogenetics, China, MycoKeys, new species, LSU rRNA, ITS region, Tremellales