Using a combined DNA dataset built from three nuclear gene regions — the internal transcribed spacer (ITS) region and partial sequences of the tef1 and tub2 genes — the team placed all six isolates into four species. Two of these proved to be undescribed: Sirococcus euryicola, isolated from healthy leaves of Eurya japonica in Yunnan Province, and Sirococcus linderae, found on healthy leaves of Lindera aggregata in Fujian Province. The remaining two isolates matched known species in new contexts: Sirococcus fujianensis was recovered from tea plant (Camellia sinensis) leaves in Fujian, a host family not previously documented for this fungus, and Sirococcus mengyinensis was found on chestnut leaves in Tai’an City, Shandong, extending its known range roughly 110 kilometres northwestward from its original discovery site in Mengyin.

The phylogenetic backbone of the study was substantial. The final alignment comprised 110 taxa and 2,474 nucleotide characters, partitioned by gene as ITS, tef1, and tub2. The researchers inferred trees using both maximum likelihood and Bayesian inference, and the two approaches produced highly consistent topologies. Within the resulting tree, the genus Sirococcus formed a well-supported monophyletic clade with full statistical support in both analyses. The new species each occupied their own distinct, highly supported branches: S. euryicola was sister to S. mengyinensis, and S. linderae was sister to S. lanceolatae. The isolates identified as S. fujianensis and S. mengyinensis each clustered tightly with the ex-type strains of their respective species, confirming their identities.

The taxonomic context of the work matters as much as the new species themselves. Sirococcus was established in 1855 and was historically known almost exclusively from asexual forms infecting coniferous trees, while a separate genus, Gnomoniopsis, described in 1893, accommodated sexual forms on broadleaf hosts. For over a century the two were treated as distinct. Molecular phylogenetics gradually undermined this split, and a recent comprehensive re-evaluation using the same three-locus dataset showed that all Gnomoniopsis species nest within Sirococcus, forming a single robustly supported lineage with indistinguishable asexual morphology. Under the principle of nomenclatural priority, Gnomoniopsis was formally synonymised under Sirococcus, with 38 new combinations proposed. The present study works within that revised framework and, together with the two new species, brings the worldwide count of Sirococcus species to approximately 40.

Describing the new species required careful morphological work alongside the genetics. Sirococcus euryicola produces pycnidial conidiomata that are yellowish-brown and solitary, with hyaline, guttulate conidia measuring (5.3–)6.2–7.8(–9.4) × (1.4–)1.6–2.0(–2.2) micrometres. On potato dextrose agar its colonies reach 73–74 millimetres in diameter after seven days in darkness. Sirococcus linderae, by contrast, has reddish-brown conidiomata and smaller conidia of (3.8–)4.8–6.0(–6.5) × (2.0–)2.2–2.6(–2.8) micrometres, with slower-growing colonies of 45–50 millimetres over the same period. Both species were distinguished from their closest relatives by a combination of sequence divergence and conidial shape and size. S. euryicola differs from S. mengyinensis by 1.9 percent in ITS, 11.5 percent in tef1, and 6.8 percent in tub2, while S. linderae differs from S. lanceolatae by 8.5, 39.2, and 28.1 percent at the same three loci respectively.

The two new records were confirmed with equally conservative criteria. The S. fujianensis strain from tea leaves showed 0 percent ITS divergence from the ex-type strain, 0.64 percent in tef1, and 0.23 percent in tub2 — all far below the interspecific thresholds commonly applied in the genus — and its conidial dimensions overlapped completely with the type. The S. mengyinensis strain from Shandong chestnut leaves showed similarly small intraspecific differences. Notably, both the original isolate and the new one came from symptomatic chestnut leaves, suggesting an association with chestnut leaf lesions, although the authors caution that the species’ precise pathogenic potential and ecological niche remain to be elucidated.

Beyond describing new taxa, the study tackled a persistent problem in delimiting Sirococcus species on Chinese chestnut (Castanea mollissima). The phylogenetic tree recovered a poorly supported clade containing four species: S. xishuangbannaensis, S. yunnanensis, S. taishanensis, and S. chinensis, arranged in two pairs. A critical evaluation showed that S. xishuangbannaensis and S. yunnanensis differ by 8 out of 502 sites in ITS — exceeding the interspecific threshold — along with stable differences in conidial size, so both were retained as distinct. The pair S. taishanensis and S. chinensis presented the opposite puzzle: near-identical sequences at all three loci, yet consistent differences in conidiomata form, conidial dimensions, colony appearance, and the tissues from which each was originally isolated. Lacking additional intermediate isolates and experimental evidence on phenotypic plasticity, the authors refrained from synonymising them and flagged the pair as needing further sampling.

Ecologically, the findings reshape the picture of where Sirococcus occurs and what it does. The genus is now known to associate with at least ten plant families, including Fagaceae, Rosaceae, Pinaceae, Theaceae, Lauraceae, and Melastomataceae. Some species are strict host specialists, such as S. chamaemori on cloudberry, while others are generalists; the new host record of S. fujianensis on tea represents a jump across distantly related plant families from its original Castanopsis host. Many species are endophytic or latent pathogens — the two new species were both isolated from healthy leaves — whereas others cause shoot blight, leaf spots, or nut rot, with S. smithogilvyi threatening chestnut production across Europe, North America, and Oceania. The authors note that endophytic species may become pathogenic under stress or favourable conditions, and that host shifts could lead to emerging diseases, although the pathogenic potential of most isolates in this study remains uncharacterised.

To aid future identification, the authors compiled a dichotomous key to all approximately 40 known Sirococcus species, incorporating characters such as perithecia, asci, ascospores, conidiomata, conidiogenous cells, conidia, and host association. Holotype and paratype specimens are deposited in the Herbarium of Shandong Agricultural University, with ex-type cultures preserved in the Shandong Agricultural University Culture Collection and the China General Microbiological Culture Collection Center. The team concludes that large-scale surveys covering broader geographical ranges, more host groups, and diverse plant tissues are needed to uncover the genus’s cryptic diversity and clarify its ecological functions — a reminder that even well-studied fungal orders still hold substantial undiscovered diversity in China’s forests.

Subject of Research: Diversity and taxonomy of the fungal genus Sirococcus on woody hosts in Fujian, Shandong, and Yunnan, China

Article Title: Morphological and multilocus phylogenetic analysis of Sirococcus ( Diaporthales , Gnomoniaceae ) on woody hosts from Fujian, Shandong, and Yunnan, China: Two new species and two new records

Article References: Wang, Y., Liu, Q., Zhang, M., Zhang, Z., Zhang, X., & Li, Z. (2026). Morphological and multilocus phylogenetic analysis of Sirococcus (Diaporthales, Gnomoniaceae) on woody hosts from Fujian, Shandong, and Yunnan, China: Two new species and two new records. MycoKeys, 142, 239–264. https://doi.org/10.3897/mycokeys.142.207158

Image Credits: AI Generated

DOI: 10.3897/mycokeys.142.207158

Keywords: Sirococcus, Diaporthales, Gnomoniaceae, new fungal species, China, endophytic fungi, plant pathogens, multilocus phylogeny, chestnut, Castanea mollissima, Camellia sinensis, fungal taxonomy