Approximately 50% of the native vascular plant flora of the Hawaiian Islands is threatened or endangered. Primary threats are from habitat conversion and the introduction and spread of alien plants, animals, and various pathogenic organisms. Native Hawaiian fern species comprise about 17% of the native vascular plant flora and they dominate some ecosystems. Although fern species do not generally suffer any unusual threats relative to those experienced by other plants, they are subject to the same stresses and threats that are leading to the demise of many plant taxa. We have conducted population genetic studies of 15 Hawaiian fern species in the genera Adenophorus, Asplenium, Dicranopteris, Odontosoria, and Sadleria. From those surveys we inferred levels and patterns of genetic diversity at three geographic scales: within populations, within islands, and across islands. Although there was some variation across species, we generally found that individual local populations and/or island-populations exhibited genetic endemism in the form of unique alleles. This genetic uniqueness suggests that conspecific populations on different islands should be managed as distinct conservation-management units. In addition, we infered that most species reproduced sexually and that most individual sporophytes were produced via outcrossing. In the face of shrinking population sizes, such historically outcrossing taxa are likely to suffer from inbreeding depression due to the increased expression of deleterious alleles normally masked from expression in heterozygotes. Estimates of minimum-viable-population size for the rare species Adenophorus periens suggested that the only large, remnant population of this species may no longer have enough individuals to maintain current levels of genetic diversity over time. These genetic studies are providing insight into 1) evolutionary patterns and processes and 2) the potential impact of alternative conservation management strategies.

Key words: conservation, ferns, Hawaii, population genetics