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Pollinators play an important role in the reproduction of zoophilous plants. A shift in pollinators has often been observed for oceanic island plants, probably because of the differences in fauna. In this study, we obtained data on pollinator shifts from insects to birds in Orobanche boninsimae (Orobanchaceae), a holoparasitic plant species endemic to the Bonin (Ogasawara) Islands, oceanic islands in the Pacific. We observed pollination and measured seed viability in O. boninsimae and its continental sister species O. coerulescens. We found that two passerine birds, the Japanese white‐eye (Zosterops japonicus) and bulbul (Hypsipetes amaurotis squameiceps), visited the flowers and sucked the nectar of O. boninsimae, while only insects visited those of O. coerulescens. Viable seeds were produced under pollinator‐excluded treatments in the two Orobanche species, indicating that the seeds were produced by automatic self‐pollination and/or apomixis. These results suggest that O. boninsimae may be pollinated by birds and can produce seeds by automatic self‐pollination/apomixis. This is the first record of visitation of the genus Orobanche by birds. Studies of pollination systems in native plants on the Bonin Islands are few compared to those on other oceanic islands, and O. boninsimae may provide a valuable example of pollinator shifts in the Bonin Islands. [ABSTRACT FROM AUTHOR]

Molecular phylogenetic studies have greatly improved our understanding of phylogenetic relationships of non-photosynthetic parasitic broomrapes ( Orobanche and related genera, Orobanchaceae), but a few genera have remained unstudied. One of those is Platypholis, whose sole species, Platypholis boninsimae, is restricted to the Bonin-Islands (Ogasawara Islands) about 1000 km southeast of Japan. Based on overall morphological similarity, Platypholis has been merged with Orobanche, but this hypothesis has never been tested with molecular data. Employing maximum likelihood and Bayesian analyses on a family-wide data set (two plastid markers, matK and rps2, and three nuclear markers, ITS, phyA and phyB) as well as on an ITS data set focusing on Orobanche s. str., it is shown that P. boninsimae Maxim. is phylogenetically closely linked to or even nested within Orobanche s. str. This position is supported both by morphological evidence and by the newly obtained chromosome number of 2 n = 38, which is characteristic for the genus Orobanche s. str. [ABSTRACT FROM AUTHOR]

The Bonin (Ogasawara) Islands are subtropical oceanic islands in the northwestern Pacific. Reflecting their ancient origins, previous studies on plants of the Bonin Islands reported evolutionary phenomena that are common to oceanic islands, such as high endemism and accelerated diversification. In this article, we demonstrate the first example of loss of seed dispersibility during the evolutionary processes of the plants of the Bonin Islands. Seed buoyancy and morphology of Hibiscus glaber, a tree endemic to the Bonin Islands, and H. tiliaceus, a pantropic species, were examined. The latter is the progenitor species of H. glaber. Average ratios of floating seeds per tree were 0.2 and 0.8 for H. glaber and H. tiliaceus, respectively, in a 3% NaCl solution. There was considerable variation among individual H. glaber trees, ranging from 0 to 0.89. The air space inside the seed coat was generally smaller in H. glaber than in H. tiliaceus. Loss of seed buoyancy in H. glaber is due to decreased air space in the seeds. It is plausible that loss of seed buoyancy occurred in response to the habitat shift inland during the speciation process of H. glaber from the coastal species H. tiliaceus. [ABSTRACT FROM AUTHOR]

The complete chloroplast genome sequence of a hemiparasitic plant Santalum boninense (Santalaceae) was determined and described in this study. The chloroplast genome was 144,263 bp in length, consisting of a large single-copy region (83,912 bp), a small single-copy region (11,349 bp), and inverted repeats (24,501 bp). The chloroplast genome contained 124 genes including 72 protein-coding genes, 35 tRNA genes, eight rRNA genes, and nine pseudogenes. All the ndh genes and infA gene were found to lose function by gene loss or pseudogenization. GC content of the whole chloroplast genome was 38.0%. [ABSTRACT FROM AUTHOR]

Rubus boninensis is a rare endemic species found on the Bonin Islands with a very restricted distribution. It is morphologically most closely related to Rubus trifidus, occurring widely in the southern Korean peninsula and Japan. This species pair provides a good example of anagenetic speciation on an oceanic island in the northwestern Pacific Ocean—R. trifidus as a continental progenitor and R. boninensis as an insular derivative species. In this study, we firstly characterized the complete plastome of R. boninensis and R. trifidus and compared this species pair to another anagenetically derived species pair (R. takesimensis–R. crataegifolius). The complete plastome of R. trifidus was 155,823 base pairs (bp) long, slightly longer (16 bp) than that of R. boninensis (155,807 bp). No structural or content rearrangements were found between the species pair. Eleven hotspot regions, including trnH/psbA, were identified between R. trifidus and R. boninensis. Phylogenetic analysis of 19 representative plastomes within the family Rosaceae suggested sister relationships between R. trifidus and R. boninensis, and between R. crataegifolius and R. takesimensis. The plastome resources generated by the present study will help elucidate plastome evolution and resolve phylogenetic relationships within highly complex and reticulated lineages of the genus Rubus. [ABSTRACT FROM AUTHOR]

Since floras of oceanic islands are distinct from those of the closest continents, islands can serve as useful systems for understanding the evolution of host specificity during speciation of parasitic plants. Orobanche boninsimae (Orobanchaceae) is a holoparasitic plant species endemic to the isolated Bonin (Ogasawara) Islands; previous observations suggested several possible host species for O. boninsimae. In this study we sought to provide more definitive identification of O. boninsimae host plants through DNA analyses of host plant roots. We investigated nine populations of O. boninsimae from Chichijima and Hahajima Islands and determined their hosts by DNA barcoding of the chloroplast trnH-psbA region. We determined that three endemic woody species, Ochrosia nakaiana (Apocynaceae), Melicope grisea (Rutaceae), and Melicope nishimurae (Rutaceae), and one exotic tree, Bischofia javanica (Phyllanthaceae), were host species of O. boninsimae. These three families are newly recorded as hosts for the genus Orobanche , suggesting that O. boninsimae might have developed these unique host specificities in the islands. In addition, we established that O. boninsimae parasitizes completely different species between the islands, even though all available host species of O. boninsimae execpt for M. nishimurae were commonly distributed throughout these islands. This result suggests that intraspecific differentiation for host preference and possibly cryptic speciation has occurred between isolated islands. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ochrosia is widely distributed genus from the West Indian Ocean to the Middle Pacific. • Phylogeny of Ochrosia focused on the biogeography of island endemics is presented. • Two endemic species on the Bonin Islands had distinct phylogenetic origins. • The two endemic species were independently derived about 1–2 million years ago. • Complex origins of flora in oceanic islands are demonstrated. The genus, Ochrosia , is widely distributed from the West Indian Ocean throughout tropical Asia to the Middle Southern Pacific region. Ochrosia comprises many island-endemic species, suggesting that long-distance dispersal and isolation after migration are key factors for clarifying the diversification process. However, the phylogeny and biogeography of endemic Ochrosia species have not been evaluated well due to the difficulty of adequate sampling from the entire distribution range of the genus. In this study, we focused on two Ochrosia species endemic to the Bonin (Ogasawara) Islands in the northwest Pacific. The Bonin Islands are of volcanic origins and consist of two islands groups, the Ogasawara and Volcano Islands groups, approximately 300 km apart. Ochrosia nakaiana is endemic to the Ogasawara Islands group, whereas O. hexandra is endemic to the Volcano Islands group. To elucidate the phylogenetic positions of these two endemic Ochrosia species, we conducted molecular phylogenetic studies with dating and biogeographic analyses including other Ochrosia species. The phylogenetic trees showed that the two endemic species had distinct origins; O. nakaiana was closely related to O. oppositifolia and O. iwasakiana , whereas O. hexandra was related to O. mariannensis. Based on the chloroplast DNA phylogeny, the genus, Ochrosia , divided into two major lineages 36.6 million years ago. Further, the two endemic species of the Bonin Islands were independently derived approximately 1–2 million years ago. Ochrosia nakaiana originated from the Southeast Asia, New Caledonia, or other Pacific Islands, while O. hexandra derived from O. mariannensis in Micronesia. We demonstrated different origins of the two endemic Ochrosia species on the Bonin Islands. This study provided an excellent example of the complex origins and speciation of flora in the oceanic islands. [ABSTRACT FROM AUTHOR]