Mind the gap: global targets and strategies for ex situ conservation of critically endangered plants

Abstract An estimated 45% of plants are threatened with extinction, with those classified as “Critically Endangered” (CR) by the International Union for Conservation of Nature at the highest risk and in urgent need of ex situ conservation. We performed a gap analysis of CR plants stored in in the Millennium Seed Bank Partnership (MSBP), a global network spanning 101 countries and territories, to assess their current conservation status and guide future seed collection priorities. The MSBP currently holds 2,507 accessions of 474 CR taxa, representing 0.9% of the 52,874 taxa banked and 7.21% of all CR taxa. While most collections have relatively good general information available (information index = 0.81), key aspects such as viability (viability index = 0.31) and genetic diversity (genetic diversity index = 0.31) remain poorly documented. Only 9.49% of conserved CR taxa have sufficient seed numbers (≥ 1,050 seeds from ≥ 50 individuals) for restoration research, and just 5.49% have been collected from ≥ 5 populations and ≥ 50 individuals across their native distribution. Overall, 6,120 CR plant taxa remain unbanked, of which 11.58 to 17.17% (depending on model) require alternative conservation methods due to desiccation-intolerant seeds. However, the majority (23.32–68.74% taxa) are likely suitable for traditional seed banking techniques (drying to 15% relative humidity and freezing at -20℃). The desiccation sensitivity of 14.02–65.16% taxa remains unknown, requiring urgent research. Ensuring comprehensive ex situ conservation of CR taxa will require strategic investment and capacity building to meet global biodiversity conservation needs.