Hidden Fungal Worlds Inside Brazilian Orchid Roots Yield Ten New Species

Deep inside the healthy roots of wild Brazilian orchids, an extraordinary hidden diversity has come to light. A new study published in IMA Fungus reports that fungi of the family Chaetomiaceae, common in soils and decaying plant material but poorly documented inside living plants, are far more diverse in orchid roots than anyone expected. Of 51 fungal isolates analyzed from the Atlantic Forest and Cerrado biomes, 19 isolates turned out to represent ten species entirely new to science, distributed across six genera. The discovery, based on a rigorous combination of microscopic morphology and multigene DNA phylogenetics, not only expands a family of economically important fungi but also underscores how much remains unknown about the microbial partners living quietly within plant tissues.

The research focused on one of the most species-rich families of flowering plants on Earth: the Orchidaceae, which comprises 29,524 species found on every continent except Antarctica. Brazil alone is home to an estimated 2,692 native orchid species, roughly 1,490 of them endemic, making the family the second most diverse flowering plant group in the country after the legumes. Yet many of these species remain poorly studied, and habitat loss combined with collection for trade continues to threaten them. Because orchid seeds lack sufficient nutrients to germinate on their own, every wild orchid depends on symbiotic fungi to complete its life cycle, making the fungi associated with orchid roots a matter of both ecological urgency and scientific fascination.

While the mycorrhizal partners that feed orchid seedlings have received considerable attention, a different class of fungal guests, the endophytes, colonize root tissues without causing disease and often without any visible symptoms. These fungi, mostly ascomycetes, can confer real benefits to their hosts, including promotion of plant growth, resistance to pathogens, and tolerance of abiotic stress, while they themselves receive shelter and nutrients from the plant. Previous surveys of orchid endophytes, however, relied heavily on sequencing just the internal transcribed spacer (ITS) region of ribosomal DNA, a marker now recognized as too coarse to distinguish closely related fungal species. That limitation left the true identity of chaetomium-like fungi in orchid roots largely unresolved.

The new study took a different approach. Working as part of the Brazilian PROTAX research program, the team sampled the roots of twelve wild orchid species spanning epiphytic, lithophytic, and terrestrial lifestyles, including familiar genera such as Cattleya, Catasetum, Habenaria, Zygopetalum, Acianthera, Eulophia, Polystachya, Gomesa, Cyclopogon, and others. Collections spanned four states: Distrito Federal, Goias, Minas Gerais, and Rio de Janeiro. Using indirect isolation and dilution-to-extinction cultivation methods, plus direct isolation of fungal structures from the coconut shell substrate used to grow one Cattleya species, the researchers obtained 44 root endophyte isolates, three saprophytic isolates from the substrate, and four additional strains including endophytes from banana and cacao roots that proved closely related to their orchid finds.

Each isolate was then subjected to a polyphasic analysis combining colony growth on four standardized culture media with detailed micromorphology of ascomata, ascomatal hairs, asci, ascospores, and asexual structures, and DNA sequencing of four loci: ITS, the 28S large subunit (LSU), beta-tubulin (tub2), and the RNA polymerase II second-largest subunit (rpb2). Because ITS and LSU have limited resolving power at the species level in this family, the protein-coding genes tub2 and rpb2 were amplified first for all isolates, providing the resolution needed to recognize species boundaries. Bayesian inference and maximum-likelihood phylogenies were constructed, and candidate new species were delimited using the Genealogical Concordance Phylogenetic Species Recognition framework, which demands consistent evolutionary signal across multiple independent loci.

The results were striking. The 51 isolates belonged to six genera: Arcopilus, Chaetomium, Collariella, Dichotomopilus, Humicola, and Pseudohumicola. Arcopilus proved the most diverse, with 21 isolates and eight species, four of them new: A. abbreviatus and A. endophyticus, both from the terrestrial orchid Habenaria petalodes; A. kasuyae, from the lithophytic Acianthera teres and named in honor of Brazilian microbiologist Maria Catarina Megumi Kasuya, a pioneer of orchid-fungus research in Brazil; and A. singularis, from Cattleya locatellii. Two of these new Arcopilus species are morphologically aberrant: A. endophyticus forms sterile colonies with coiled, melanized hyphae and no reproductive structures, while A. singularis produces an acremonium-like asexual morph never before documented in the genus.

The remaining new species spanned four other genera. Collariella fluminensis, found in the roots of Cyclopogon congestus and Eulophia maculata in Rio de Janeiro and Minas Gerais, was the only new species recovered from two different host plants. Dichotomopilus brasiliensis was isolated from Zygopetalum mackayi and, notably, also from banana and cacao roots, hinting at a broad host range. Three new Humicola species emerged: H. capillata from the Cerrado in the Distrito Federal, and H. paraisoensis and H. purpurea, the latter named for its striking purple pigment, from Atlantic Forest sites in Minas Gerais. Finally, Pseudohumicola crispata, recovered from a lithophytic Cattleya, is the first species of its genus anywhere in the world to be described from an endophytic association.

The phylogenetic data also forced two taxonomic reckonings. Chaetomium albiziae, described only recently as an endophyte of Albizia lebbeck, clustered consistently within the C. cucumericola clade, with pairwise sequence identities of about 99 percent across ITS, tub2, and rpb2 and only negligible single-nucleotide differences. Because the original description of C. cucumericola was based on a sterile isolate, the sexually reproducing C. albiziae effectively supplies that species’ missing sexual morph, and the authors formally synonymized the two names. A parallel conclusion placed Arcopilus albae under A. cupreus, since the former differed from the reference strain of A. cupreus by only two single-nucleotide mutations and was morphologically indistinguishable. By contrast, Chaetomium microthecium, which sometimes nests inside the broad C. globosum complex in some gene trees, was deliberately retained as a distinct species pending a comprehensive revision of that complex.

Beyond the novelties, the study delivered a cascade of first records. Arcopilus aureus, the type species of its genus, and A. cupreus were both documented as orchid endophytes for the first time, as was A. macrostiolatus, previously known from Nigerian forest soil. Chaetomium coarctatum, C. cochliodes, C. pseudocochliodes, and C. tenue were all newly recorded for Brazil and as orchid endophytes, while Dichotomopilus variostiolatus was reported for the first time inside orchid roots. Two previously known Pseudohumicola species gained richer descriptions: the acremonium-like synanamorph of Ps. cinnamomeobrunnea, originally described from volcanic soil in the Canary Islands, and the sexual morph of Ps. pulvericola, originally found in house dust in Mexico, which revealed itself as homothallic when cultivated on oatmeal agar under a sterile paper filter.

The broader significance is twofold. Ecologically, the findings reveal that chaetomium-like fungi form complex communities inside wild orchid roots across three different plant lifestyles and two major Brazilian biomes, even though the precise function of these associations remains unclear. Economically, Chaetomiaceae are already prized for degrading cellulose-rich substrates and producing secondary metabolites with agricultural, pharmaceutical, and industrial applications, and endophytic Arcopilus and Humicola isolates have shown antifungal, antibacterial, antioxidant, and pigment-producing capabilities. With only 22 species identified here from limited sampling, almost half of them new to science, the study makes a vivid case that Brazil’s orchid roots are a frontier of fungal discovery, and that taxonomic exploration of these partnerships is the essential first step toward understanding them and harnessing their potential.

Subject of Research: Diversity and taxonomy of endophytic Chaetomiaceae fungi associated with roots of wild Brazilian orchids

Article Title: Diversity and taxonomy of endophytic Chaetomiaceae ( Sordariales ) associated with roots of wild Orchidaceae in Brazil

Article References: Ramos, D. O., Nogueira, P. T. S., Condé, T. O., dos Santos Santana, J., & Pereira, O. L. (2026). Diversity and taxonomy of endophytic Chaetomiaceae (Sordariales) associated with roots of wild Orchidaceae in Brazil. IMA Fungus, 17, Article e192047. https://doi.org/10.3897/imafungus.17.192047

Image Credits: AI Generated

DOI: 10.3897/imafungus.17.192047

Keywords: Chaetomiaceae, endophytic fungi, Orchidaceae, Brazil, taxonomy, new species, multigene phylogeny, Atlantic Forest, Cerrado, mycology, Arcopilus, Chaetomium