Tracing the Biogeographical Origins of a Clade of Island-Hopping Hibiscus
Islands are known for their unique biodiversity which largely arose through dispersal from mainlands and subsequent allopatric speciation. The Island Biogeography Theory posits that mainlands nearest to islands should contribute the most to the composition of island floras, a pattern that has often been demonstrated. An alternative history for the origin of island taxa is that some groups have evolved to be island specialists, dispersing between distant islands while skipping nearby mainlands. An ideal system to study this alternative pattern is an enigmatic group of island specialists in the genus Hibiscus section Lilibiscus. Section Lilibiscus contains ~23 species found principally on islands from Madagascar, the Mascarene Islands, Fiji and Vanuatu, to the Hawaiian archipelago. The most famous of these species is the horticulturally important Hibiscus rosa-sinensis. Species in this group are also culturally important in many Melanesian and Polynesian societies. The overarching goals of our project are to: 1) confirm the biogeographic origins of sect. Lilibiscus; 2) test the hypothesis that the group originated in Madagascar and subsequently colonized oceanic islands globally; 3) assess the genetic diversity among wild populations of as many species as possible; 4) assess the genetic diversity of ex-situ collections with the intent of augmenting both in-situ and ex-situ diversity.
The taxonomic history of Hibiscus sect. Lilibiscus make it a difficult group to study. Due to the considerable beauty and ease of cultivation of species in sect. Lilibiscus, many early European explorers brought propagules back to their country of origin. Some of these collections were brought into cultivation with incomplete, incorrect, or speculative information about their origins. Species in sect. Lilibiscus also hybridize easily, leading to species names being misused for interspecific hybrids or propagated sports. In addition, habitat loss on the islands where these species occur has resulted in seven species now being listed by the IUCN as critically endangered or even extirpated from the wild. For example, Hibiscus denisonii is known only from cultivation, but has a proposed Fijian origin. It is possible that this species is actually a hybrid from the mid-nineteenth century. Finally, sect. Lilibiscus has been little sampled in recent phylogenies of Hibiscus, so the relationships of many species and the boundaries of the group are difficult to define.
In order to achieve each of our goals, our research group has organized systematic collections of Hibiscus sect. Lilibiscus species across the group’s range. However, certain species are difficult to access or are known only in cultivation. Currently, we are requesting samples from two species for which we have poor sampling: H. denisonii, discussed above, and H. insularis, from Phillip Island (a tiny island south of Norfolk Island in the South Pacific Ocean). Acquiring samples of these two species will complete our sampling of Hibiscus sect. Lilibiscus, allowing us to accomplish goals 1 & 2, and make progress in goals 3 & 4. If you have any information or questions about our research, feel free to contact Brock Mashburn.
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