Extreme Reproductive Constraints Under Pollinator Scarcity in the Endangered Orchid Calanthe aristulifera: Five-Year Preliminary Monitoring in South Korea

Calanthe aristulifera is an endangered terrestrial orchid that has historically suffered from severe illegal poaching. However, little is understood regarding population dynamics for remaining C. aristulifera populations. This study presented the first record on the size, reproduction rate, and insect visitors of C. aristulifera populations on an oceanic island from 2021 to 2025, to identify threatening factors and provide conservation implications. Throughout the study period, complete absence of fruit set of C. aristulifera was found (natural fruit set ratio: 0%). This reflects the reproductive failure as an on-going threatening factor, regardless of the yearly variations in total number of C. aristulifera individuals (198–253) and flowering rate (62.2–87.4%). The known pollinators (Eucera nipponensis and Lasioglossum occidens) were undetected near C. aristulifera populations, which coincided with complete reproductive failure. Insects like Callipora lata, Episyrphus balteatus, and Bibio tenebrosus visited to C. aristulifera flowers, but direct field and photographic observations showed no pollinia removal by such insects. Overall results highlight that conservation programs should adopt management practices to attract effective pollinators to C. aristulifera populations. Ex situ conservation may also be an option to facilitate in vitro propagation experiments, and help the remaining C. aristulifera to avoid severe reproductive constraints.