Hong Kong orchids on the EDGE: a phylogenetic framework for conservation planning, trade mitigation and population...

Hong Kong, a vital part of the Indo-Burma Biodiversity Hotspot, harbours a significant portion of China's orchid diversity within a limited area. This unique flora faces severe treats from habitat degradation, illegal collection and trade, placing many species disproportionately at risk at the local level. Effective conservation prioritization is urgently needed. This study applies the latest EDGE framework to Hong Kong's orchids, integrating phylogenetic distinctiveness with extinction risk to identify conservation priorities and establishing a scientific basis for targeted protection and rescue.

We compiled a comprehensive checklist of Hong Kong orchids and constructed a time-calibrated phylogeny using nuclear (ITS) and plastid (trnL-F, matK, trnH-psbA) sequence data. The EDGE2 metric, integrating Evolutionary Distinctiveness (ED) and extinction risk from regional and national Red Lists, was applied to identify conservation priorities. Correlations between threat status and four traits (habit, habitat specificity, mating system and occurrence in trade) were also examined.

Our assessment revealed that a significantly higher proportion of Hong Kong's 138 native orchid taxa, comprising 134 species and four varieties, are threatened locally (76 taxa in the Hong Kong Red List) compared to nationally (43 taxa in the China Red List). Phylogenetic analysis of 134 taxa (130 species and four varieties) revealed a significant correlation between ED and Hong Kong Red List status, and EDGE2 analysis using local Red List data highlighted Vanilla shenzhenica, Nervilia plicata, Apostasia nipponica, Bletilla striata and Acanthophippium gougahense as the greatest priorities. Moreover, local threat status exhibited significant positive correlations with habit, habitat specificity, mating system and trade.

The EDGE2 framework effectively balances immediate extinction risk with the preservation of evolutionary history, revealing critical disparities between local and national threat assessments. Importantly, it identifies evolutionarily distinct species overlooked by threat-based methods alone. Positive correlations corroborate an association between threat status and certain ecological traits. Altogether, these findings advocate for the integration of phylogenetic and trait-based approaches into regional conservation strategies to effectively safeguard Hong Kong's unique orchid diversity and its evolutionary heritage, offering a model for other regions globally.