Three new species of Colletotrichum (Glomerellales, Glomerellaceae) associated with walnut (Juglans regia) anthracnose from China Author Li, Yixuan https://orcid.org/0009-0007-6862-9605 State Key Laboratory of Efficient Production of Forest Resources, Beijing Forestry University, Beijing 100083, China Author Lin, Lu 0000-0003-3456-3760 State Key Laboratory of Efficient Production of Forest Resources, Beijing Forestry University, Beijing 100083, China Author Cao, Jing Key Laboratory for Silviculture and Conservation of the Ministry of Education, Beijing Forestry University, Beijing 100083, China Author Gan, Mingxu Ankang Forestry Technology Promotion Centre, Ankang, Shaanxi 725099, China Author Fan, Xinlei 0000-0002-4946-4442 State Key Laboratory of Efficient Production of Forest Resources, Beijing Forestry University, Beijing 100083, China text MycoKeys 2024 2024-09-03 108 147 167 journal article 302170 10.3897/mycokeys.108.125382 075e3ed0-d39a-42ac-8440-ea366739f8b6 Colletotrichum siamense Prihastuti, L. Cai & K. D. Hyde , Fungal Divers. 39: 98 (2009) Materials examined. China . • Sichuan Province , Guangyuan City , Chaotian District , Zhongzi Town , 32 ° 41 ' 05 " N , 106 ° 02 ' 08 " E , from leaf of Juglans regia L. , 10 Oct. 2023 , Y. X. Li , L. Lin & X. L. Fan ( BJFC - S 2231 , living culture CFCC 59601 ; BJFC - S 2233 , living culture CFCC 59625 ; BJFC - S 2235 , living culture CFCC 59964 ) ; • 32 ° 41 ' 34 " N , 106 ° 02 ' 23 " E , from leaf of Juglans regia L. , 10 Oct. 2023 , Y. X. Li , L. Lin & X. L. Fan ( holotype BJFC - S 2234 , living culture CFCC 59909 ) Notes. Colletotrichum siamense was first described as a species in association with Coffea arabica by Prihastuti et al. (2009) . The broader concept of C. siamense sensu lato has been a subject of considerable debate, as noted by Weir et al. (2012) and Sharma et al. (2015) , due to the application of the Genealogical Concordance Phylogenetic Species Recognition ( GCPSR ) approach. Liu et al. (2016) concluded that C. siamense is a single species, not a species complex. Based on phylogenetic evidence, Zhang et al. (2022) proposed that C. menglaense , C. pandanicola , and C. parvisporum are synonyms of C. siamense . More recent studies have further synonymized the closely related species C. rhizophorae and C. thailandica with C. siamense , considering morphological characteristics, phylogenetic analyses, and GCPSR ( Aumentado et al. 2024 ). In this study, C. siamense was isolated from walnut leaf spots affected by walnut anthracnose. The four isolates our study examined while forming a distinct lineage were found within the C. siamense clade in our phylogenetic analysis. Moreover, our isolate ( CFCC 59909) is similar to the holotype of C. siamense ( ICMP 18578). While the conidia of our isolate ( CFCC 59909) are wider than strain ICMP 18578 (12.3–14.5 × 4.9–6.4 vs. 7–18.3 × 3–4.3 μm) ( Prihastuti et al. 2009 ). Based on this evidence, we identify our isolate as C. siamense .