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• Premise of the study: The monogeneric family Ruppiaceae is found primarily in brackish water and is widely on all continents, many islands, and from subartic to tropical zones. Ruppia taxonomy has been confusing because of its simplified morphology yet high phenotypic plasticity and the existence of polyploidy and putative hybrids. This study addresses the current classification of species in the genus, the origin of putative hybrids and polyploids, and the distribution of Ruppia species. • Methods: Separate molecular phylogenetic analyses using plastid DNA and nuclear-encoded PHYB data sets were performed after chromosome observations. • Key results: The resultant trees were largely congruent between genomes, but were incongruent in two respects: the first incongruence may be caused by long outgroup branches and their effect on ingroup rooting, and the second is caused by the existence of heterogeneous PHYB sequences for several accessions that may reflect several independent hybridization events. Several morphological species recognized in previous taxonomic revisions appear paraphyletic in plastid DNA and PHYB trees. • Conclusions: Given the molecular phylogenies, and considering chromosome number and morphology, three species and one species complex comprising six lineages were discerned. A putative allotriploid, an allotetraploid, and a lineage of hybrid origin were identified within the species complex, and a hybrid was found outside the species complex, and their respective putarive parental taxa were inferred. With respect to biogeography, a remarkably discontinuous distribution was identified in two cases, for which bird-mediated seed dispersal may be a reasonable explanation. [ABSTRACT FROM AUTHOR]

Two woodyHibiscusspecies co-occur in the Bonin Islands of the northwestern Pacific Ocean:Hibiscus glaberMatsum. is endemic to the islands, and its putative ancestral species,Hibiscus tiliaceusL., is widely distributed in coastal areas of the tropics and subtropics. To infer isolating mechanisms that led to speciation ofH. glaberand the processes that resulted in co-occurrence of the two closely related species on the Bonin Islands, we conducted molecular phylogenetic analyses on chloroplast DNA (cpDNA) sequences. Materials collected from a wide area of the Pacific and Indian Oceans were used, and two closely related species,Hibiscus hamaboSiebold Zucc. andHibiscus macrophyllusRoxb., were also included in the analyses. The constructed tree suggested thatH. glaberhas been derived fromH. tiliaceus,and that most of the modern Bonin populations ofH. tiliaceusdid not share most recent ancestry withH. glaber.Geographic isolation appears to be the most important mechanism in the speciation ofH. glaber.The co-occurrence of the two species can be attributed to multiple migrations of different lineages into the islands. While a wide and overlapping geographical distribution of haplotypes was found inH. tiliaceus, localized geographical distribution of haplotypes was detected inH. glaber. It is hypothesized that a shift to inland habitats may have affected the mode of seed dispersal from ocean currents to gravity and hence resulted in geographical structuring ofH. glaberhaplotypes. [ABSTRACT FROM AUTHOR]