New evidence of ectomycorrhizal fungi in the Hawaiian Islands associated with the endemic host Pisonia sandwicensis (Nyctaginaceae)

Ectomycorrhizal plants and fungi are ubiquitous in mainland forests, but because of dispersal limitations are predicted to be less common on isolated islands. For instance, no native ectomycorrhizal plants or fungi have ever been reported from Hawaii, one of the most remote archipelagos on Earth. Members of the plant tribe Pisonieae are common on many islands, and prior evidence shows that some species associate with ectomycorrhizal fungi. However, until now, the Pisonieae species of Hawaii had yet to be examined for their mycorrhizal status. Here we sampled roots from members of the genus Pisonia growing on the Hawaiian islands of Oahu, Maui and Hawaii. We used molecular and microscopic techniques to categorize trees with respect to their mycorrhizal associations. We report that the Hawaiian endemic Pisonia sandwicensis forms ectomycorrhizas with at least five fungal operational taxonomic units (corresponding closely to species) belonging to four genera. We also report that this tree species is monophyletic with other ectomycorrhizal Pisonia species. We suggest that in light of the newly discovered Hawaiian ectomycorrhizal fungal community and other island ectomycorrhizal communities, dispersal limitations do not prevent the colonization of remote islands by at least some ectomycorrhizal fungi.