Origin of Hawaiian ferns of the genus Ctenitis (Dryopteridaceae)

The Hawaiian Islands are an emblematic field to study evolution, with their very high rates of endemism and spectacular cases of insular speciation. Nevertheless, many Hawaiian lineages still deserve investigation, such as in the fern lineage. In this study, we address the question of the origin of the fern genus Ctenitis, which is present in the archipelago with two endemic species, Ctenitis squamigera and C. latifrons. Using a taxonomic sampling covering the pantropical distribution of the genus and three chloroplast DNA regions, we provide evidence that the genus in the Hawaiian Islands originated from a single long-distance dispersal from the Neotropics. This area is less represented than Asia and the South Pacific in the origin of Hawaiian ferns, but a Neotropical origin may be explained by the transportation of spores by tropical storms originating near Central America. Furthermore, the colonization of the Hawaiian Islands is estimated to have occurred between 4 [9-2] and 3 [7-1] mya. This timing is consistent with the ages of all main and extant islands of the archipelago, which already provided habitats for the establishment of the initial Ctenitis colonizer. In turn, this relatively late arrival to the islands and the related potentially low availability of ecological niches may have hampered diversification of the genus beyond the two extant species.

Automated summary

This study investigates the origin of the fern genus Ctenitis in the Hawaiian Islands and suggests a single long-distance dispersal event from the Neotropics. The colonization of the islands is estimated to have occurred around 3-4 million years ago, consistent with the ages of the main islands. The late arrival and potential limited ecological niches may have hindered diversification of the genus.