Morphological and DNA analyses identify two new Sutorius species in Guizhou

Researchers have identified and formally described two new species of the bolete mushroom genus Sutorius from Yuxi Town in Daozhen County, Guizhou Province, China. The species, Sutorius yuxiensis and Sutorius rubropurpureus, were recognized through an integrative assessment of their fruiting bodies, microscopic structures and DNA sequences from four gene regions. The research was a taxonomic study of boletoid fungi collected in subtropical forests and shrublands; it did not directly measure the fungi’s ecological effects in the field. Both collections nevertheless add documented diversity to a genus whose members are ectomycorrhizal fungi, a group that forms mutually beneficial associations with woody plants.

The new specimens were collected in an area with a humid subtropical monsoon climate and vegetation consisting mainly of subtropical evergreen broadleaf forests, coniferous forests and secondary shrublands. Each mushroom was photographed and described in situ, with field notes recording its macroscopic features and standardized colour descriptions. The specimens were cut longitudinally to observe discoloration in damaged tissue, then dried in an oven at 45 °C for 10 hours. Sealed with desiccant, they were temporarily stored at 4 °C in a resource-preservation facility. The examined material was deposited in the Herbarium of Cryptogams at the Kunming Institute of Botany, Chinese Academy of Sciences. The holotypes are catalogued as HKAS151561 for S. yuxiensis and HKAS151559 for S. rubropurpureus.

For microscopic examination, the dried fungi were rehydrated, sectioned and mounted in a solution containing 5% potassium hydroxide and 1% Congo red. Investigators examined basidia, basidiospores, cheilocystidia, pleurocystidia, the pileipellis and the stipitipellis, as well as internal tissue from the cap and stipe. Measurements included 30–50 randomly selected basidiospores and 20 additional microscopic structures. The researchers also extracted DNA and amplified the nuclear ribosomal large subunit region, the nuclear internal transcribed spacer, the translation elongation factor 1-alpha gene and the second largest subunit of RNA polymerase II. Their combined alignment contained 2,869 base pairs, including 839 base pairs for nrLSU, 695 for nrITS, 608 for TEF1-alpha and 727 for RPB2, with gaps.

Maximum likelihood and Bayesian inference analyses generated trees that were highly consistent, differing mainly in some statistical support values, so the researchers presented the maximum likelihood tree. Rubroboletus sinicus and Rubroboletus rhodosanguineus were used as outgroups. Sutorius yuxiensis emerged as the sister taxon of S. obscuripellis, including the available type sequences of that species, with maximum likelihood bootstrap support of 100% and a posterior probability of 1.00. S. rubropurpureus was placed within a larger clade that also contains S. rubinus, S. mucosus, S. pachypus and S. australiensis. That major branch likewise received 100% bootstrap support and a posterior probability of 1.00. Support for the specific relationship between S. rubropurpureus and S. rubinus was low, leaving that individual relationship less certain despite support for the broader lineage.

Sutorius yuxiensis has a medium-sized cap measuring 40–65 mm in diameter. Its smooth surface is densely covered with fine hairs and is yellowish-brown, with patchy colour variation, irregularly distributed spots and an occasionally fading margin. The yellowish-white cap flesh contains scattered small groups of dark reddish-brown encrustations and is unchanging or only slightly reddened when cut. Its stipe measures 40–60 by 15–20 mm and is clavate to cylindrical, with a dull violet-grey surface bearing violet-brown granulose squamules. The hymenophore is tubular, with orange-grey tubes and a pale violet-grey pore surface. The smooth, narrowly ellipsoid to subcylindrical basidiospores measure (10.33–)10.49–14.90(–14.95) by (3.13–)3.26–5.40(–5.43) μm, with a mean length-to-width ratio of 2.93 ± 0.41. Both cheilocystidia and pleurocystidia are present.

The name Sutorius yuxiensis refers to Yuxi Town, where the holotype was collected at 28°50′42″N, 107°37′32″E and an elevation of 1,184.74 m. The species can be distinguished from its closest phylogenetic relative, S. obscuripellis, by several characters. S. yuxiensis has smaller cheilocystidia and possesses pleurocystidia, whereas S. obscuripellis lacks pleurocystidia. Its pileipellis comprises brown to dark brown hyphae that are colorless to brownish-yellow or pale brown in potassium hydroxide; in S. obscuripellis, the corresponding tissue comprises brown to pale-yellow hyphae in water and shows slight extracellular brown pigmentation. The cap of S. yuxiensis is yellowish-brown, whereas S. obscuripellis has the darker brown cap. The stem cross-section of S. yuxiensis also has a dark-brown margin, a feature lacking in S. obscuripellis.

The second new species, Sutorius rubropurpureus, has a cap 40–80 mm in diameter. When young, the cap is purplish-red and tomentose, with a slightly subrugulose surface; with age, it becomes purplish-grey to brown and gradually becomes paler toward the margin. Its stipe is 30–50 by 10–20 mm, reddish-brown, cylindrical to subclavate or tapering downward, and sometimes sub-bulbous at the base. Grayish-white granulose squamules densely cover the finely scabrous surface, with white to off-white basal tomentum. The tube surface is dark purple, while the tubes are orange-brown. The cut stipe does not change colour when injured. The specific epithet refers to the conspicuous reddish-purple coloration of the pileus and stipe surfaces.

Microscopic characters further distinguish S. rubropurpureus from close relatives. Its smooth, subfusoid basidiospores measure (9.85–)9.90–15.20(–15.48) by (3.57–)3.60–5.50(–5.86) μm, with a mean length-to-width ratio of 2.86 ± 0.37. Narrowly fusiform cheilocystidia occur frequently, and spindle-shaped pleurocystidia are also present. The pileipellis is an intricate trichoderm or a slightly gelatinized version of that structure, while the stipe surface has a thin gluten layer composed of erect, thin-walled hyphae with brown extracellular pigment. These traits help distinguish the species from S. rubinus, which lacks pleurocystidia; S. mucosus, which lacks both cheilocystidia and pleurocystidia and has a waxy or subviscid cap; S. pachypus, which typically has a broader stipe; and S. australiensis, which has dark violet-brown pores when young and a differently patterned stipe surface.

The authors note that Sutorius has been taxonomically unstable since its establishment in 2012 and that superficially similar mushrooms can conceal substantial genetic differences. The type species, S. eximius, is understood to represent a complex of closely related taxa rather than a single, uniformly distributed species. Some Asian collections that resemble Sutorius in appearance have grouped within the Tylopilus lineage in molecular analyses, potentially reflecting convergent evolution or cryptic speciation. Sutorius and Neoboletus can also overlap in colour and spore ornamentation, making morphology alone unreliable in some comparisons. The study therefore used integrative identification across multiple loci, with TEF1-alpha and RPB2 providing especially useful discrimination. The authors describe Boletaceae diversity in tropical and subtropical Asia as still substantially underestimated and conclude that the two new taxa expand the known diversity of Sutorius in Guizhou’s subtropical karst forest ecosystems.

Subject of Research: Taxonomic identification of two new ectomycorrhizal Sutorius species in Guizhou, China

Article Title: Morphological and molecular evidence reveal two new species of Sutorius ( Boletaceae , Basidiomycota ) from Guizhou Province, China

Article References: Xu, X.-H., Mo, X., Chen, A.-M., Li, Y.-D., Pei, Y., Li, J.-W., Wen, T.-C., Karunarathna, S. C., Tarafder, E., & Zhang, W.-P. (2026). Morphological and molecular evidence reveal two new species of Sutorius (Boletaceae, Basidiomycota) from Guizhou Province, China. MycoKeys, 134, 275-290. https://doi.org/10.3897/mycokeys.134.192749

Image Credits: AI Generated

DOI: 10.3897/mycokeys.134.192749

Keywords: Sutorius, new species, fungal taxonomy, Boletaceae, phylogenetics, mushroom morphology, Guizhou, forest fungi, ectomycorrhizal fungi, molecular identification, Morphological, molecular