Two New Sooty Mould Fungi Discovered on Leaves in Guizhou, China

Deep in the subtropical forests of Guizhou Province, China, two previously unknown species of sooty mould fungi have been formally identified on the surfaces of living leaves. Researchers from Guizhou University describe the fungi as Trichomerium guiyangense and Trichomerium xishuiense, two new members of a genus of foliar epiphytic fungi that coat leaf surfaces in dark, intricately interwoven mats of hyphae. The discovery, published in the journal MycoKeys, expands the known diversity of a lineage that has long puzzled mycologists and highlights how much fungal life remains undocumented even in well-studied regions.

The genus Trichomerium belongs to the family Trichomeriaceae within the order Chaetothyriales, a group of fungi that includes species capable of causing plant diseases as well as opportunistic pathogens of humans and animals. Members of this family display a remarkable range of ecological adaptations, with some species inhabiting rock surfaces and architectural relics as rock-inhabiting fungi, while others thrive as epiphytes on living leaves, particularly in tropical rainforests. The family currently accommodates twelve genera, including Anthracina, Arthrocladium, Bradymyces, Formicomyces, Incumbomyces, Knufia, Lithohypha, Neostrelitziana, Pararthrophiala, Pasadenomyces, Strelitziana, and Trichomerium itself, which serves as the type genus for the family.

Trichomerium was first introduced by the Italian mycologist Spegazzini in 1918 with Trichomerium coffeicola as the type species, and its taxonomic placement has shifted repeatedly over the past century. It was initially classified in Capnodiaceae, later transferred to Triposporiopsidaceae, and then moved to Chaetothyriaceae based on morphological data before molecular phylogenetics revealed that Trichomerium species form a distinct cluster separate from both of those families. What sets the genus apart morphologically is a combination of features: an apical ascus ring, ascospores with or without sheaths, and unique septation patterns. The sexual morph produces superficial, setiferous, uniloculate ascomata surrounded by loosely interwoven mycelium, which release bitunicate asci containing hyaline, septate ascospores. The asexual morph is equally distinctive, producing dark, multi-segmented conidia that aggregate into star-like structures with multiple radiating arms.

Despite the genus being formally recognized for over a century, its taxonomy remains surprisingly incomplete. Index Fungorum currently lists 34 records of Trichomerium, yet sequence data are available for only 21 species, and the actual number of valid species is believed to be far fewer than the number of names in circulation. Many species were originally described without molecular sequence data, making it difficult to assess which names correspond to genuinely distinct organisms. This gap between nomenclature and verifiable biology underscores the urgent need for further taxonomic and ecological research to fill in the missing pieces of the genus’s evolutionary story.

The two new species were discovered during fieldwork at two locations in Guizhou Province. Leaves exhibiting symptoms of black mildew infection were collected from Aha Lake Wetland Park in Guiyang City and from Xishui County. The specimens were carefully transported to the laboratory in paper envelopes and maintained in a dry setting to preserve their integrity. Pure cultures were obtained using a single-spore isolation method, in which a single ascoma was submerged in sterile distilled water on a microscope slide to facilitate the release of ascospores. The resulting spore suspension was placed onto water agar plates and incubated at ambient temperature for 8 to 12 hours to allow germination. Individual germinated ascospores were then transferred to potato dextrose agar plates and incubated at 25 degrees Celsius for 15 to 20 days until colonies nearly covered the entire plate.

Macroscopic features were observed and photographed using a Keyence VHX-7000 digital stereomicroscope, while diagnostic morphological features were examined under a Zeiss Axioscope 5 compound microscope and captured with an AxioCam 208 color camera. Multiple measurements of each feature were recorded using ZEN 2.0 software. Type specimens were deposited in the Herbarium of the Department of Plant Pathology, Agricultural College, Guizhou University, and ex-type cultures were preserved in the university’s culture collection. The new species names were registered at Index Fungorum and assigned identifiers.

For molecular characterization, total genomic DNA was extracted directly from the cultures, and two genetic loci were amplified: the internal transcribed spacer region (ITS) and a segment of the large subunit rDNA (LSU). The ITS sequences comprised 449 characters, including 233 constant sites, 169 parsimony-informative sites, and 218 distinct site patterns, while the LSU sequences comprised 1,017 characters with 819 constant sites, 101 parsimony-informative sites, and 237 distinct site patterns. Phylogenetic analyses were conducted using a combined dataset of 34 species representing the family Trichomeriaceae, with Phaeosaccardinula ficus and P. multiseptata designated as outgroups. Bayesian inference and maximum likelihood analyses produced topologies that were consistent with each other, and the maximum likelihood tree was used to illustrate the phylogenetic placement of the new species.

The results revealed that the family Trichomeriaceae comprises twelve distinct lineages corresponding to the twelve recognized genera, and notably, Trichomerium and Formicomyces are sister genera. Trichomerium guiyangense, collected from living leaves of Iris species in Guiyang City, forms a distinct clade with high node support (ML/BI = 92/1) and is phylogenetically distant from neighboring species. BLAST comparisons revealed 10 percent nucleotide differences in ITS and 2 percent in LSU compared to T. cicatricatum, and 4 percent in ITS and 2 percent in LSU compared to T. camporesii. Morphologically, T. guiyangense is distinguished by its large ascomata reaching up to 196 micrometres in diameter, its 2-seriate ascospores, and its larger asci measuring 45.5 to 54.1 by 10.4 to 18.2 micrometres, which differ from those of closely related species.

Trichomerium xishuiense, collected from Xishui County, presents an even more intriguing phylogenetic picture. The strain forms an independent branch within the Trichomerium clade with maximum statistical support (ML/BI = 100/1), yet it occupies a position outside the core Trichomerium group, adjacent to Formicomyces. This placement raises the possibility that it may not belong to Trichomerium in the strictest sense. However, the species exhibits the characteristic sexual morph of Trichomerium, including setose ascomata and bitunicate asci, whereas Formicomyces has only ever been found in its asexual phase, producing distinctive funnel-shaped or cup-like conidiophore structures. Compared to its closest sister species T. bambusae, T. xishuiense shares 11 percent sequence divergence in the ITS region and differs in having larger ascomata up to 260.4 micrometres in diameter, sessile and larger asci, and 1-to-2-septate, constricted ascospores rather than 3-septate, non-constricted ones.

The discovery of these two species contributes valuable molecular data for future phylogenetic studies within the family and expands the known diversity of Trichomerium in China. However, the researchers note that significant gaps remain in the classification of the genus and its associated foliar fungal communities. Many previously described species, including the type species of the genus itself, lack reference sequences for key genetic markers such as ITS and LSU, and the integration of morphological characteristics with molecular data has not been systematically pursued. The authors emphasize that future research should prioritize expanding molecular marker coverage through multi-locus sequencing, developing a unified taxonomic framework that combines morphological and molecular evidence, and establishing a more robust phylogenetic system. Such advances will greatly enhance understanding of the biodiversity patterns and evolutionary history of Trichomerium and its relatives across the fungal tree of life.

Subject of Research: Taxonomic description of two new Trichomerium fungal species from Guizhou Province, China

Article Title: Two new species of Trichomerium ( Trichomeriaceae , Chaetothyriales ) from Guizhou Province, China

Article References: Deng, X., Liu, Y., Hongsanan, S., Yang, T., Feng, Y., Sun, J., & Zeng, X.-Y. (2026). Two new species of Trichomerium (Trichomeriaceae, Chaetothyriales) from Guizhou Province, China. MycoKeys, 137, 223-239. https://doi.org/10.3897/mycokeys.137.177643

Image Credits: AI Generated

DOI: 10.3897/mycokeys.137.177643

Keywords: Trichomerium, Trichomeriaceae, Chaetothyriales, sooty moulds, fungal taxonomy, Guizhou Province, China, phylogenetics, ITS, LSU rDNA, new species, mycology