The specimens at the heart of the study were collected between 2015 and 2017 and brought to a mycological laboratory in paper bags for examination. One fungus was found growing as a saprobe on the dead rachis — the central stalk — of an unidentified fern in Baoshan. The other two were isolated from dead aerial twigs of Japanese maple (Acer palmatum) and ginkgo (Ginkgo biloba) in Kunming. All three were saprobes, meaning they feed on dead organic material rather than attacking living tissue, at least as far as current observations show. That ecological role makes them important, if inconspicuous, players in nutrient cycling within their habitats.

Identifying a new fungal species today requires far more than a careful look through a microscope. The researchers combined detailed morphological characterization with multilocus DNA phylogenetics, sequencing four genetic markers: the internal transcribed spacer region (ITS), the large subunit of nuclear ribosomal DNA (LSU), the second largest subunit of RNA polymerase II (rpb2), and the beta-tubulin gene (tub2). These four regions were aligned and analyzed together using both maximum likelihood and Bayesian inference methods, the two workhorse approaches of modern molecular systematics. Only when the DNA evidence and the physical characteristics of the fungi agreed that a specimen did not match any known species did the team formally describe it as new.

The phylogenetic analyses were substantial undertakings. For the genus Didymella, the team built a dataset of 97 strains spanning 2,412 aligned characters, rooted with Epicoccum brahmanense as an outgroup. Within this tree, the new species Didymella baoshanensis emerged as a distinct sister lineage to the type strain of D. brevipilosa, a relationship supported by strong statistical values: 97 percent maximum likelihood bootstrap support and a Bayesian posterior probability of 1.00. The two species then clustered with several other Didymella species, including D. pteridis and D. viburnicola, in a broader subclade. Morphologically, D. baoshanensis is distinguished by its multi-loculate ascostromata — fruiting bodies divided into several internal chambers — along with flask-shaped, ostiolate ascomata, eight-spored bitunicate asci, and fusiform, one-septate, hyaline ascospores.

Interestingly, the closest known relative of D. baoshanensis occupies a very different niche. While D. brevipilosa was isolated from plant debris submerged in freshwater in Spain and has been found on fir buds in Canada, the new species was collected from a dead, hanging fern rachis in the mountains of Yunnan. Only a handful of Didymella species have ever been reported from fern hosts, and for several of those, molecular data are still lacking, leaving their exact placement unresolved. The discovery of a well-supported fern-associated lineage therefore adds a valuable piece to the puzzle of how this large genus has diversified across plant hosts.

The genus Didymella itself carries a long and tangled taxonomic history. First erected in 1880 by the Italian mycologist Pier Andrea Saccardo, with D. exigua as its type species, the genus was shuffled among numerous families over the following decades — from Sphaeriaceae to Mycosphaerellaceae, Phaeosphaeriaceae, Pleosporaceae, and Venturiaceae — before molecular phylogenetics finally anchored it within the family Didymellaceae, which was established in 2009 based on a neotype study of D. exigua. Today, more than 500 species epithets are listed under Didymella in major nomenclatural databases, yet fewer than half have been clarified through molecular phylogeny and studies of both their sexual and asexual forms. More than 200 species described in the eighteenth and nineteenth centuries remain taxonomically unresolved, awaiting re-examination of type material with modern methods.

The two new Nothophoma species tell a similar story of hidden diversity within a younger genus. Nothophoma was established in 2015 to accommodate phoma-like fungi that formed a distinct evolutionary lineage separate from Phoma sensu stricto, and it currently includes 26 accepted species. Some of these show striking host specificity — N. infossa is consistently associated with ash trees, while N. gossypiicola has only been found on cotton — while others occur as saprobes, pathogens, or endophytes across a wide range of plants, and a few have even turned up in human clinical samples such as bronchial washes. In the phylogenetic tree built from 45 strains, Nothophoma aceris formed a well-supported sister lineage to a taxon published as N. juglandis, with 98 percent bootstrap support and a posterior probability of 1.00, while N. ginkgonis occupied a distinct basal branch relative to N. ferruginea, N. platycladi, and N. pruni.

Morphologically, the two new Nothophoma species are subtle but distinguishable. Nothophoma aceris produces small, globose, dark brown pycnidia — asexual fruiting bodies — with phialidic conidiogenous cells and conidia that start hyaline and mature to brown or dark brown, thick-walled and non-guttulate. It can be separated from its close relatives by a combination of smaller conidiomata, conidial dimensions and wall thickness, and the absence of the papillate or elongated necks seen in species such as N. spiraeae. Nothophoma ginkgonis, by contrast, has subglobose to hemispherical, single-loculate conidiomata and conidia that age to a light brown or yellowish-brown hue, larger than those of its relative N. platycladi and broader than those of N. pruni. Because these fungi look so similar to one another, the authors emphasize that morphology alone is insufficient for species delineation; the multilocus DNA evidence is what clinches each species’ identity.

One of the study’s more intriguing taxonomic findings concerns the invalidly published name N. juglandis. That name, proposed for a fungus causing heart rot disease of walnut in Beijing, failed to meet the requirements of the International Code of Nomenclature for algae, fungi, and plants — specifically, the rules requiring a clearly designated type and, for cultures described after 2019, a statement that the type culture is preserved in a metabolically inactive state. As a result, N. juglandis is not validly published and must be formally validated before it can be used. The close phylogenetic relationship between N. aceris and the walnut fungus suggests that the N. quercina species complex, already known to encompass several poorly resolved species, may harbor even more undescribed diversity than currently recognized.

Yunnan Province has repeatedly been identified as one of China’s great hotspots of fungal diversity, and recent surveys of dead bamboo, woody litter, herbaceous plants, and grassland ecosystems continue to turn up new species, new records, and poorly known lineages. The three species described here reinforce a growing consensus among mycologists: dead twigs, rachises, and other decomposing plant tissues are among the most rewarding substrates for discovering fungi that have never been catalogued. The authors also note that the potential pathogenicity of the two new Nothophoma species deserves further investigation, since several of their relatives are known plant pathogens. For now, though, the message is one of humility about how much remains unknown — three new species from a handful of dead branches, in a genus where hundreds of old names still await clarification, suggest that the fungal census of Yunnan is only just beginning.

Subject of Research: Taxonomy and multilocus phylogenetics of newly discovered Didymellaceae fungi in Yunnan, China

Article Title: Uncovering hidden diversity in Didymellaceae from Yunnan: Introducing three novel species of Didymella and Nothophoma

Article References: Phookamsak, R., Jiang, H., Li, J., Chomnunti, P., Qi, H., Bhat, D. J., Kumla, J., Xu, J., Al-Ani, L. K. T., Lumyong, S., & Suwannarach, N. (2026). Uncovering hidden diversity in Didymellaceae from Yunnan: Introducing three novel species of Didymella and Nothophoma. MycoKeys, 141, 283-313. https://doi.org/10.3897/mycokeys.141.205517

Image Credits: AI Generated

DOI: 10.3897/mycokeys.141.205517

Keywords: mycology, Didymellaceae, Didymella, Nothophoma, Yunnan, fungal taxonomy, phylogenetics, saprobes, new species, ascomycetes, China, biodiversity