Understanding Germination Cues and Seed Viability for Rare Plant Taxa on California’s Channel Islands

Background/Question/Methods

California’s Channel Islands are a biodiversity hotspot and include many rare and endemic species. In recent history, humans have altered these island plant communities by introducing non-native species. As a result, rare plants on the Channel Islands have reduced in distribution and remain threatened. Due to the inherent nature of rare plants, understanding their unique attributes proves difficult for long term conservation. To better understand rare species and maximize their re-establishment, this study investigates germination cues for the seeds of 5 rare plant taxa from the Channel Islands: Boechera hoffmannii, Gilia tenuiflora ssp. hoffmannii, Berberis pinnata ssp. insularis, Malacothrix foliosa ssp. polycephala and Dudleya traskiae. Seeds were obtained from the Santa Barbara Botanic Garden’s Conservation Seed Bank or collected from the museum’s living collection. Boechera hoffmannii and Gilia tenuiflora ssp. hoffmannii were studied in a time series with accessions of various collection dates to better understand their success after long term storage across different times in history. Berberis pinnata ssp. insularis, Malacothrix foliosa ssp. polycephala and Dudleya traskiae underwent initial germination tests. Germination was recorded daily until all or most seeds germinated while remaining seeds underwent cut tests to account for their initial viability.

Results/Conclusions

Our results indicate that seeds from ⅘ accessions for Boechera hoffmannii have high rates of germination, indicating their potential success in future restoration efforts as well as their viability success in long term storage. Gilia tenuiflora ssp. hoffmannii, Malacothrix foliosa ssp. polycephala and Dudleya traskiae experienced higher rates of germination when seeds underwent cold stratification, inferring that the germination of these species are induced by cold temperatures. Berberis pinnata ssp. insularis underwent 4 treatments: cold stratification, clipping, cold stratification + clipping, and boiling. Preliminary results indicate that cold stratification and clipping of the seed coat induce germination at a greater rate. These results can facilitate future restoration efforts and inform management for rare plants on the Channel Islands in the face of climate change.