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.

Published as part of Li, Yixuan, Lin, Lu, Cao, Jing, Gan, Mingxu & Fan, Xinlei, 2024, Three new species of Colletotrichum (Glomerellales, Glomerellaceae) associated with walnut (Juglans regia) anthracnose from China, pp. 147-167 in MycoKeys 108 on pages 147-167, DOI: 10.3897/mycokeys.108.125382