Remarkable Longevity of Herbarium-Derived Seeds of the Rare and Threatened Annual Legume Astragalus contortuplicatus L.: Germination After More Than 142 Years of Dry Storage

Seed longevity plays a crucial role in the persistence of plant populations, particularly in short-lived species inhabiting unpredictable environments. However, empirical data on long-term seed viability remain scarce, especially for rare and poorly known taxa. Astragalus contortuplicatus is a threatened annual species of periodically flooded habitats, characterized by sporadic occurrence and limited ecological knowledge; based on its annual life cycle and the temporal unpredictability of its habitat, its long-term population persistence is likely facilitated by persistent seed banks. In a previous study, we demonstrated that seeds of this species stored in herbarium collections can retain the ability to germinate for more than a century. Here, we reassess seed germination capacity after an additional 11.5–12 years of dry storage, using the same germination protocol, and analyse temporal changes based on repeated measurements of the same herbarium specimens. Germination data from 2014 and 2026 were evaluated using binomial models, and the relationship between seed age and germination capacity was examined using linear and non-linear approaches. Paired analyses revealed a significant overall decline in germination probability over time, although responses varied among specimens. Despite this decline, seeds from the oldest available sample (collected in 1883) still retained the ability to germinate, with 20% germination after approximately 142.5 years of storage. Across the full dataset, seed age had a significant negative effect on germination, and non-linear models provided a better fit than simple linear regression, indicating that the loss of germination capacity does not follow a strictly linear pattern. Our results confirm the exceptional longevity of seeds in this rare species while also demonstrating that germination capacity declines over time under continued dry storage. These findings are consistent with the ecological expectation that long-lived, dormant seeds may contribute to population persistence in unpredictable habitats, while underlining the potential of herbarium collections as valuable resources for the conservation and possible restoration of threatened plant species. Notably, seeds in the oldest sample retained the ability to germinate, emphasizing the exceptional longevity of seeds in this species.