BIOGEOGRAPHY AND PHYLOGENETICS OF THE HAWAIIAN ENDEMIC HIBISCADELPHUS, HAU KUAHIWI (MALVACEAE)

Abstract

The endemic Hawaiian flowering plant genus Hibiscadelphus was described by Joseph F. Rock based on two species found on Hawaii island and one species from Maui in 1911. In the years since, five additional species have been described, one from Hawaii island, two from Kauai, and one each from Lanai and Maui. In April 2012, A new species was discovered with a small remote population of ca. 99 mature individuals, the genus as whole is critically endangered. It had been proposed that the island colonization history of species in the genus followed the “Progression Rule”, a well-documented pattern in many Hawaiian taxa of progressive colonization from the older to younger islands, as new islands emerged from the sea. However, no molecular phylogeny has been published that tests this hypothesis for Hibiscadelphus. It is the purpose of this work to generate a phylogenetic hypothesis of Hibiscadelphus and its relationship to other genera of the Malvaceae based on chloroplast and nuclear DNA sequenced from a combination of samples from living plants, herbarium specimens, and accessions from the Hawaiian Plant DNA Library. DNA sequences were examined by both Bayesian and Maximum Likelihood approaches for phylogenetic reconstruction. Further, a fossil and island age calibrated BEAST analysis was performed with a Relaxed Log Normal molecular clock to estimate lineage divergence timing within the Hawaiian archipelago. The molecular clock estimate corroborates generally accepted dates for island ages and supports the hypothesis of the Hibiscadelphus radiation following the Progression Rule. The resulting phylogenies also indicate Hibiscadelphus as a monophyletic clade that is nested within the African Hibiscus section Calyphylli, from which they appear to have diverged approximately 10 mya. These results indicate the relationship of Hibiscus and Hibiscadelphus is paraphyletic and Hibiscadelphus should be reclassified within Hibiscus. This insight further suggests that there were five independent colonization events of Hibiscus to the Hawaiian Islands.