Foliar flavonoids distinguish cryptic species from the <i>Sorbus commixta</i> Hedl. complex in the Korean Peninsula

From the survey of 15 flavonoids across 20 Asian taxa of Sorbus, we found that flavonols were present in most taxa, while flavones were only detected in S. wilsoniana, S. amabilis in China, and unknown Korean rowan in Korea. This chemical dichotomy proved taxonomically significant within the genus. Korean rowan, a member of the S. commixta complex, exhibited distinctive flavonoid profiles that suggest it may be a cryptic species more closely related to Chinese S. amabilis than to Japanese S. commixta or S. aucuparia subsp. pohuashanensis from northeastern China. Notably, while S. ulleungensis can be morphologically distinguished from S. commixta, both share identical chemical profiles. The parallel distribution of flavone-type taxa from central China (S. wilsoniana) through eastern China (S. amabilis) to Korea suggests an early chemical divergence in eastern Asia, likely occurring during the mid-Tertiary period. This study demonstrates the utility of flavonoid analysis in resolving taxonomic relationships within the Sorbus commixta complex morphologically, particularly in cases where traditional morphological approaches have proven insufficient for species delimitation.