Subtropical evergreen broad-leaved forests represent one of the world’s major biodiversity hotspots. Compared with trees and shrubs, however, the evolutionary history of understory herbs remains poorly understood, particularly for mycoheterotrophic plants that rely on fungi for nutrition. These plants lack photosynthetic capacity and depend heavily on specific fungal partners and intact forest ecosystems, making them highly sensitive to environmental changes. Despite their ecological and evolutionary significance, the processes shaping their population history and genetic structure have long remained unclear.A research team from the South China Botanical Garden (SCBG), Chinese Academy of Sciences, investigated the fully mycoheterotrophic species Burmannia nepalensis to address this knowledge gap. By integrating plastome, nuclear microsatellite data, and species distribution modelling, the study comprehensively examined its genetic structure, demographic history, and the key drivers shaping its phylogeographic patterns across subtropical China. The results showed that: (1) B. nepalensis exhibits low genetic diversity within populations but strong genetic differentiation among populations, primarily driven by geographic isolation and historical climatic fluctuations; (2) both molecular data and species distribution models support the existence of multiple glacial refugia during the Last Glacial Maximum, mainly located in the Nanling Mountains, Wuyi Mountains, and southwestern karst regions, thereby challenging the classical model of “southward contraction during glaciations followed by northward expansion”; and (3) demographic analyses indicate post-glacial population expansion, followed by a marked decline in effective population size around 3,000 years ago, likely associated with human-induced habitat fragmentation.This study highlights the combined roles of geographic isolation and historical climate dynamics in shaping the genetic structure of B. nepalensis, and provides empirical evidence for the presence of multiple northern glacial refugia in subtropical China. The findings also suggest that understory herbs dependent on stable forest habitats are highly vulnerable to environmental changes and anthropogenic disturbance, underscoring the urgent need for habitat conservation to ensure their long-term persistence.The study, entitled “Historical Climatic Fluctuations and Geographic Isolation Shaped the Phylogeographic Patterns of a Mycoheterotrophic Species in Subtropical China,” was published in Biological Diversity. Dr. SHI Miaomiao from SCBG is the first author, and Prof. TU Tieyao and Prof. ZHANG Dianxiang are the corresponding authors. This work was supported by the National Natural Science Foundation of China, the Guangdong Provincial Special Fund for Natural Resource Affairs on Ecology and Forestry Construction, and the Fund of the Guangxi Key Laboratory of Plant Conservation and Restoration Ecology in Karst Terrain. Article link: https://doi.org/10.1002/bod2.70021Figure 1. Habitat and morphology of Burmannia nepalensis.（Image by SHI et al.）Figure 2. Predicted potential distribution of suitable habitats for Burmannia nepalensis during the Last Glacial Maximum (LGM), the mid-Holocene (MH), and the present.（Image by SHI et al.）Figure 3. Genetic structure of Burmannia nepalensis inferred from nuclear microsatellite markers, together with haplotype distribution and phylogenetic relationships based on plastome data.（Image by SHI et al.）