Seed dormancy break and germination by a rare relict of the Wurmian glaciation in the Iberian Peninsula: Euonymus latifolius (Celastraceae)

Southern European peninsulas have repeatedly played notable roles as refuges in the natural history of flora during periods of glaciation. Euonymus latifolius (Celastraceae) is a relict species from the last Wurmian glaciation in the Iberian Peninsula. It still lives with isolated populations in favourable, cool mountainous microhabitats, being an extremely rare, critically endangered species. These Iberian populations are often high-priority targets for conservation due to their long-term persistence and unique evolutionary trajectory. Previously, it has not been feasible to promote significant programmes for reintroduction and/or population reinforcement of this singular plant species due to the great difficulties of conventional propagation. In this study, we analysed the effects of temperature, light and gibberellic acid (GA(3)) on the germination responses of E. latifolius to develop an effective protocol for seed germination as a main outcome. The results are coherent with the climatic temperature conditions recorded broadly in the Iberian Peninsula in the past and in the current refuge locations for the taxon. The germination responses of E. latifolius are compatible with those of seeds with intermediate physiological dormancy. In particular, the seeds required a 10-week warm period (20/7 degrees C + 15/4 degrees C) followed by 20 weeks of cold period (5 + 1.5 degrees C) to break dormancy and achieve germination values over 90%. GA(3) also promoted germination (80%). Therefore, we developed the first effective protocol for promoting E. latifolius seed germination and, thus, sexual propagation, to facilitate urgent ex situ actions in the current climate change context.

Automated summary

Southern European peninsulas have historically served as refuges for flora during glaciation periods, and Euonymus latifolius (Celastraceae) is a critically endangered species that has persisted in isolated populations in the Iberian Peninsula. Previous attempts to reintroduce and reinforce populations of this species were hindered by difficulties in conventional propagation methods. This study developed an effective protocol for seed germination of E. latifolius through an analysis of temperature, light, and gibberellic acid (GA(3)). The results align with past and current climate conditions in the Iberian Peninsula, and provide a strategy for ex situ actions in the face of climate change.