Dwiki Prasetiyap1, Kyong-Sook Chung2, and Hyosig Won1

1Department of Biological Science, Daegu University, Gyungsan, Gyungbuk, South Korea; 2Department of Medicinal Plant Science, Jungwon University, Goesan, Chungbuk, South Korea

Carex sect. Siderostictae, an early-diverging lineage within Carex (Cyperaceae), is of particular interest due to its restricted distribution in East Asia. Of the 13 recognized species, four occur in South Korea: C. siderosticta, C. ciliatomarginata, C. okamotoi, and C. splendentissima. While C. siderosticta and C. ciliatomarginata are widespread across East Asia, C. okamotoi and C. splendentissima are endemic to Korea and exhibit narrower, partly sympatric distributions. Previous molecular phylogenetic analyses based on nuclear rITS sequences suggested parallel speciation events between widespread and Korean-endemic species pairs (e.g., C. siderosticta sister to C. okamotoi, and C. ciliatomarginata sister to C. splendentissima). However, the sister relationship between the C. siderosticta and C. okamotoi remained ambiguous, as C. okamotoi was nested within the C. siderosticta clade, likely due to sequence heterogeneities in nrITS. Here, we reconstructed the phylogenetic relationships among the four Korean Siderostictae species by cloning the nrITS region to resolve intragenomic variation. We also investigated the ecological drivers of speciation in the two species pairs using species distribution models (SDMs). The cloned nrITS sequences of C. siderostica formed several distinct clusters, while C. okamotoi formed a single cluster nested within the C. siderosticta clade, supporting a scenario of parapatric speciation from C. siderosticta. In contrast, C. ciliatomarginata and C. splendentissima exhibited a pattern consistent with typical cladogenetic speciation. Ecological niche modeling indicated that niche divergence in these pairs is shaped primarily by ecological filtering and local adaptation rather than by geographic isolation, likely reflecting parapatric and/or sympatric speciation processes. Paleodistribution models revealed substantial range shifts and expansion from the Last Glacial Maximum to the present, while future projections under climate change scenarios predicted species-specific range expansions or contractions. Overall, this study highlights the value of integrating phylogenetic data with SDMs to refine species boundaries and elucidate the evolutionary and ecological dynamics of Carex sect. Siderostictae.