Seed dormancy and germination of an endangered coastal plant Eryngium maritimum (Apiaceae)

Eryngium maritimum is a coastal plant of the Apiaceae family. This species is threatened in several countries where it reaches the northern limits of its distribution area. Existing populations in the Baltic Region and Scandinavia are potentially affected by the low efficiency of its generative reproduction. We studied physiological aspects of its germination and dormancy breaking requirements using seeds collected from two Latvian populations. Seeds were subjected to cold and warm stratification and treatment with gibberellic acid. We monitored the development of seed embryos throughout the process of stratification at different temperatures and built a size-class structure of embryo development within a batch of seeds to visualize the developmental progress and to compare different treatments. The final germination percentage and germination rate increased after cold stratification at 5 °C in seeds germinated at 25/10 °C. Maximum germination was achieved after four months of cold stratification. Treatment with gibberellic acid had a similar dormancy breaking effect that was enhanced by previous warm stratification. The relative size of embryos increased during cold stratification, although this increase was not uniform. We conclude that in seeds of E. maritimum, embryo growth during stratification is required before germination can start and that growth is enhanced by warm stratification. Breaking the physiological component of seed dormancy requires cold stratification that can be substituted by treatment with gibberellic acid. We suggest that germination characteristics of seeds and the structure of embryo development within seeds in a particular population may reflect the state of the plant population itself and provide valuable information for research on the biology of this species.