Genetics and germination of the endangered bog bird's-foot trefoil (Hosackia pinnata; Fabaceae) in Canada

Hosackia pinnata (bog bird’s-foot trefoil) is an endangered legume in Canada that is restricted to Vancouver Island, British Columbia, but populations exist in western U.S.A. We provide the first status update for this species in Canada since 2003 and the first evaluation of genetic diversity. Germination trials tested the efficacy of soil type, cold stratification, and heat shock treatments. Genetic analyses, using 3,811 SNPs across 53 samples, estimated genetic diversity, differentiation, inbreeding, kinship and population genetic structure. Two subpopulations had declined by 78-92%. Germination rates were low (2.75%) but long periods of cold stratification, and heat shock were beneficial. Genetic diversity and differentiation were moderate for the larger subpopulations around Harewood Plains. Several subpopulations exhibited inbreeding. Genetic clustering consistently separated subpopulations in the Extension, Harewood Plains and Woodley areas, with K=3 or 4 appearing optimal in explaining the data. Our genetic data suggest H. pinnata may have been introduced into Canada, historically. However, this hypothesis requires further testing across the geographic range of the species. Our work serves as a baseline for future studies and management, and indicates that ex situ germination may be used as a means of preventing continued decline of Canadian H. pinnata populations.