Deep in the rivers and streams of southern China, a quiet world of decomposers is only now coming into focus. Mycologists surveying submerged decaying wood in Guizhou and Hainan Provinces have uncovered two previously unknown species of saprobic fungi, formally described as Hyaloambispora aquatica and Paramirandina fusiseptata in the journal MycoKeys. Both belong to the family Microthyriaceae within the order Microthyriales, a group of microfungi best known for their distinctive reproductive structures. The discovery, based on a combination of detailed microscopy and multigene DNA analysis, expands the known diversity of freshwater fungi in Asia and offers fresh clues about how these organisms have evolved to exploit life underwater.
The fieldwork behind the discovery stretched over nearly four years, from September 2021 to May 2025. Researchers collected samples of decaying wood that had been submerged in freshwater habitats, sealed them in plastic bags with locality and habitat details, and transported them to the laboratory. There, the samples were incubated in plastic boxes lined with moistened tissue for one to two weeks, allowing any fungal colonizers to grow and sporulate. This simple but effective technique encourages wood-inhabiting fungi to reveal themselves, producing the spore-bearing structures that taxonomists rely on for identification.
Under the microscope, the two new species showed the classic features of hyphomycetes, asexually reproducing fungi that form conidiophores, specialized stalks that bear spores at their tips. Hyaloambispora aquatica produces erect, unbranched, dark brown conidiophores measuring roughly 119.5 to 167.5 micrometers in length, topped by polyblastic, sympodial conidiogenous cells that generate distinctive fusiform, reniform or obpyriform conidia, meaning spores shaped like spindles, kidneys or inverted pears. Each conidium is divided by three septa, with a swollen central cell that is olivaceous to pale brown, flanked by subhyaline apical and basal cells. The species name aquatica refers directly to its aquatic home.
Paramirandina fusiseptata, collected from Longli County in Guizhou Province, builds similar conidiophores but on a larger scale, ranging from 208.5 to 273 micrometers long. Its conidia are fusiform and three-euseptate, with a pale brown to brown central cell that sets it apart from all previously described members of the genus, whose spores are hyaline, or glassy and colorless. The species epithet fusiseptata captures exactly this combination of spindle-shaped, septate spores with a darkened middle cell. Both species were cultured on potato dextrose agar, where their colonies grew slowly, reaching only about 12 to 13 millimeters in diameter after more than 40 days at room temperature.
Morphology alone, however, is no longer sufficient to describe a new fungal species, especially in groups where similar-looking genera abound. To pin down the identity of their four isolates, the researchers extracted genomic DNA from fresh mycelia and amplified five genetic loci: the large and small ribosomal RNA gene regions LSU and SSU, the internal transcribed spacer region ITS, and the protein-coding genes tef1-alpha and rpb2. These five markers were then combined into a concatenated dataset of 4,307 characters covering 62 taxa, with two species of Kirschsteiniothelia serving as outgroups to root the tree.
The phylogenetic analyses, run with both Maximum Likelihood and Bayesian Inference methods, delivered a clear verdict for one of the two species. The two isolates of Hyaloambispora aquatica formed a well-supported clade, with 82 percent Maximum Likelihood bootstrap support and a Bayesian posterior probability of 1, positioned as sister to Hyaloambispora drungiorum, one of only two species previously known in the genus. Base pair comparisons reinforced the separation: the ex-type strain of the new species differs from H. drungiorum at 17 of 746 LSU positions, roughly 2.3 percent divergence. Combined with shorter conidiophores and the absence of guttulate, oil-droplet-bearing spores, the evidence justified naming a new species.
The story of Paramirandina fusiseptata proved more complicated. Its isolates formed a sister clade to Paramirandina cymbiformis, though with weak statistical support, and BLASTn searches of GenBank returned a patchwork of closest matches, including the type species P. aquatica and, curiously, Pleurotheciopsis bramleyi, whose LSU sequence shared 99.64 percent similarity. Despite this molecular ambiguity, the striking morphological differences, particularly the brown central cell in otherwise hyaline conidia, convinced the authors that their isolates represent something new. They tentatively assigned the strains to Paramirandina while acknowledging that the genus’s phylogenetic position remains insufficiently resolved due to limited multilocus sequence data.
This tension between appearance and ancestry is a recurring theme in freshwater mycology. The authors note that both new species closely resemble members of the genera Nakatopsis and Pleurotheciopsis, which share macronematous, mononematous conidiophores and sympodial conidiogenous cells. Distinguishing these lineages depends on subtle conidial characters: Hyaloambispora has three-septate spores with a swollen, brownish central cell, Paramirandina’s type species produces hyaline, two- to six-septate spores that may occur in chains, and Pleurotheciopsis bears hyaline, catenate conidia from denticles. Molecular data for Pleurotheciopsis exist for only a few taxa, and the authenticity of some deposited sequences has been questioned, since no voucher examination or detailed morphological assessment accompanied their original submission. In the study’s trees, Pleurotheciopsis tropicalis clustered with Ochroconis dracaenae rather than with either new genus, underscoring how much taxonomic housekeeping remains to be done.
The broader context makes the find more significant. Microthyriaceae, established by Saccardo in 1883 with Microthyrium as its type genus, currently comprises 20 accepted genera, several of them described only in the past few years. Hyaloambispora itself was erected in 2025, known exclusively from its asexual morph and only from freshwater habitats in north-western Yunnan Province. The new record from Hainan extends the genus’s range considerably and marks the first report of Hyaloambispora from Guizhou. Paramirandina, established in 2023, now contains four species, all described from freshwater habitats in China, a pattern that suggests these microfungi are far more diverse in Asian aquatic ecosystems than global records currently reflect.
Why should anyone care about fungi growing on soggy sticks? Freshwater saprobes are the engines of nutrient cycling in streams and rivers, breaking down lignin and cellulose in submerged wood and leaf litter and making that carbon available to the rest of the food web. Each newly described species is also a data point in the race to document fungal biodiversity before habitats change, and an anchor for understanding how aquatic lifestyles evolved repeatedly across the fungal tree of life. The specimens are preserved in the Herbarium of the Guizhou Academy of Agriculture Sciences, with living cultures deposited in the Guizhou Culture Collection, ensuring that future researchers can re-examine the material and refine the evolutionary picture as more sequences become available. For now, two small, spindle-spored decomposers have joined the catalog of life, discovered by patient observation of the wood at the bottom of southern China’s rivers.
Subject of Research: Taxonomy and multigene phylogeny of two new freshwater saprobic fungi in Microthyriaceae from southern China
Article Title: Two new species of Hyaloambispora and Paramirandina ( Microthyriaceae , Microthyriales ) from freshwater habitats in China
Article References: Shao, L., Liu, Y., Shi, Y., Liu, Y., Yang, W., & Ma, J. (2026). Two new species of Hyaloambispora and Paramirandina (Microthyriaceae, Microthyriales) from freshwater habitats in China. MycoKeys, 136, 271-284. https://doi.org/10.3897/mycokeys.136.199668
Image Credits: AI Generated
DOI: 10.3897/mycokeys.136.199668
Keywords: freshwater fungi, Hyaloambispora aquatica, Paramirandina fusiseptata, Microthyriaceae, Microthyriales, saprobic fungi, China, phylogenetics, taxonomy, conidia, decaying wood, biodiversity
News Source: Roger Howard. (October 19, 2026). Two New Freshwater Fungi Species Discovered on Sunken Wood in Southern China. Scienmag.
