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Gene flow between sympatric congeneric plants is thought to be very common and may pose serious threats to endangered species. In the present study, we evaluate the genetic diversity and divergence of three sympatric Rhododendron species in Jiaozi Mountain using newly developed microsatellites through the Illumina MiSeq sequencing approach. Genetic diversity of all three Rhododendron species studied was moderate in comparison to genetic parameters previously reported from species of this genus. Interestingly, genetic structure analysis of the three species identified a possible hybrid origin of the threatened Rh. pubicostatum. This sympatry should be considered a unimodal hybrid zone, since Rh. pubicostatum is predominant here. Unimodal hybrid zones are uncommon in Rhododendron, despite the fact that hybridization frequently occurs in the genus. Issues pertaining to the conservation of Rh. pubicostatum resulting from admixture of genetic material from its parental species are discussed.

Plant diversity is currently being lost at an unprecedented rate, resulting in an associated decrease in ecosystem services. About a third of the world's vascular plant species face the threat of extinction due to a variety of devastating activities, including, over-harvesting and over exploitation, destructive agricultural and forestry practices, urbanization, environmental pollution, land-use changes, exotic invasive species, global climate change, and more. We therefore need to increase our efforts to develop integrative conservation approaches for plant species conservation. Botanical gardens devote their resources to the study and conservation of plants, as well as making the world's plant species diversity known to the public. These gardens also play a central role in meeting human needs and providing well-being. In this minireview, a framework for the integrated missions of botanical gardens, including scientific research, in/ex situ conservation, plant resource utilization, and citizen science are cataloged. By reviewing the history of the development of Kunming Botanical Garden, we illustrate successful species conservation approaches (among others, projects involving Camellia, Rhododendron, Magnolia, Begonia, Allium, Nepenthes, medicinal plants, ornamental plants, and Plant Species with Extreme Small Populations), as well as citizen science, and scientific research at Kunming Botanical Garden over the past 80 years. We emphasize that Kunming Botanical Garden focuses largely on the ex situ conservation of plants from Southwest China, especially those endangered, endemic, and economically important plant species native to the Yunnan Plateau and the southern Hengduan Mountains. We also discuss the future challenges and responsibilities of botanical gardens in a changing world, including: the negative effects of outbreeding and/or inbreeding depression; promoting awareness, study, and conservation of plant species diversity; accelerating global access to information about plant diversity; increasing capacity building and training activities. We hope this minireview can promote understanding of the role of botanical gardens. Keywords: Botanical gardens, Citizen science, Conservation biology, Endangered plants, Germplasm, Horticulture

Manglietia ventii is a highly endangered plant species endemic to Yunnan province in China, where there are only five known small populations. Despite abundant flowering there is very low fruit and seed set, and very few seedlings in natural populations, indicating problems with reproduction. The causes of low fecundity in M. ventii are not known, largely because of insufficient knowledge of the species pollination ecology and breeding system. We conducted observations and pollination experiments, and analyzed floral scents to understand the pollinator–plant interactions and the role of floral scent in this relationship, as well as the species breeding system. Like the majority of Magnoliaceae, M. ventii has protogynous and nocturnal flowers that emit a strong fragrance over two consecutive evenings. There is a closing period (the pre-staminate stage) during the process of anthesis of a flower, and we characterize the key flowering process as an “open-close-reopen” flowering rhythm with five distinct floral stages observed throughout the floral period of this species: pre-pistillate, pistillate, pre-staminate, staminate, and post-staminate. Flowers are in the pistillate stage during the first night of anthesis and enter the staminate stage the next night. During anthesis, floral scent emission occurs in the pistillate and staminate stages. The effective pollinators were weevils (Sitophilus sp.) and beetles (Anomala sp.), while the role of Rove beetles (Aleochara sp.) and thrips (Thrips sp.) in pollination of M. ventii appears to be minor or absent. The major chemical compounds of the floral scents were Limonene, β-Pinene, α-Pinene, 1,8-Cineole, Methyl-2-methylbutyrate, p-Cymene, Methyl-3-methyl-2-butenoate and 2-Methoxy-2-methyl-3-buten, and the relative proportions of these compounds varied between the pistillate and staminate stages. Production of these chemicals coincided with flower visitation by weevils and beetles. The results of pollination experiments suggest that M. ventii is pollinator-dependent, and low seed set in natural populations is a result of insufficient pollen deposition. Thus, conservation of the species should focus on improving pollination service through the introduction of genetically variable individuals and increase in density of reproducing trees.

Magnolia sinica is one of the most threatened trees endemic to Southeast Yunnan. Based on our investigations, only 52 individuals and eight populations are found in the wild. M. sinica has been categorized as Critically Endangered on the IUCN Red List and identified as a “Plant Species with Extremely Small Populations (PSESP)”. Its fruit/seed set is very low and seedlings are rarely found in the wild. It is hypothesized that it may encounter obstacles to reproductive success. This study, therefore, focuses on its reproductive biology, knowledge of which is essential for effective conservation. Flowers of this species are protogynous and nocturnal, and possess a two-day rhythm of sexual presentation. For the first night of anthesis, the flowers are in the pistillate stage during which tepals open at dusk and close approx. 1 h later (except for the open outer ones). They remain closed until the next afternoon, when flowers, now in the staminate stage, re-open and remain so until the tepals drop. Nocturnal beetles enter into the flowers and remain trapped throughout the night as the flower closes, during which time they feed on tepals. Pollen-gathering bees are found to visit the re-opened flowers and the beetles are released during this stage. Two species of Pleocomidae and Curculionidae beetles appear to be effective pollinators. M. sinica is a self-compatible, pollinator-dependent species, and its fruit/seed set can be significantly increased by hand-pollination. No functional seed dispersers have been found in its extant natural habitats. These findings suggest that it may face both pollination and seed disperser insufficiencies in its current fragmented habitats, which may account for its low regeneration. Here we propose conservation strategies based on our findings.

Of the genus Craigia, widespread in the Tertiary, only two relict species survived to modern times. One species is now possibly extinct and the other one, Craigia yunnanensis, is severely endangered. Extensive surveys have located six C. yunnanensis populations in Yunnan province, southwest China. Using fluorescent amplified fragment length polymorphism (AFLP), the genetic diversity and population structure of these populations were examined. It was found that genetic diversity of C. yunnanensis was moderate at the species level, but low at regional and population levels. Analysis of population structure showed significant genetic differentiation between Wenshan and Dehong regions, apparently representing two geographically isolated for long time refuges. There are also clear indications of isolation between populations, which, together with anthropogenically caused decline of population size, will lead to general loss of the species genetic variation with subsequent loss of adaptive potential. To conserve the genetic integrity of C. yunnanensis, we recommend that ex-situ conservation should include representative samples from every population of the two differentiated regions (e.g. Wenshan and Dehong). The crosses between individuals originated from different regions should be avoided because of a high risk of outbreeding depression. As all the extant populations of C. yunnanensis are in unprotected areas with strong anthropogenic impact, there is no alternative to reintroduction of C. yunnanensis into suitable protected locations.

Pollination and seed dispersal in angiosperms have long been investigated in order to understand the coevolution of plants and animals. However, the signals from flowers and/or seeds to attract pollinators and/or seed dispersers have received comparatively little attention. In this study, the pollination biology and seed dispersal of the vulnerable agarwood plant Aquilaria sinensis (Lour.) Gilg, a traditional medicinal plant in China, was studied in its natural distribution range. The reproductive tactics of A. sinensis were studied in detail by employing various tests dealing with fruit set and also seed dispersal. Dynamic headspace extraction followed by GC-MS analysis was also performed in order to reveal the composition of floral scent. The results showed that noctuids and pyralids are the most effective pollinators of pollinator-dependent A. sinensis. The main compounds of the floral scent were (E, E)-α-Farnesene (61.9 ± 3.2%), trans-Ocimene (16.6 ± 1.2%), and Benzyl salicylate (4.6 ± 1.1%). The results obtained from seed dispersal experiments indicate that hornets are effective seed dispersers and they may play an important role in long-distance seed dispersal of A. sinensis. Based on our findings, we recommend several protection methods for this threatened agarwood plant in China.

Approximately one fifth of the world's plants are at risk of extinction. Of these, a significant number exist as populations of few individuals, with limited distribution ranges and under enormous pressure due to habitat destruction. In China, these most-at-risk species are described as ‘plant species with extremely small populations’ (PSESP). Implementing conservation action for such listed species is urgent. Storing seeds is one of the main means of ex situ conservation for flowering plants. Spore storage could provide a simple and economical method for fern ex situ conservation. Seed and spore germination in nature is a critical step in species regeneration and thus in situ conservation. But what is known about the seed and spore biology (storage and germination) of at-risk species? We have used China's PSESP (the first group listing) as a case study to understand the gaps in knowledge on propagule biology of threatened plant species. We found that whilst germination information is available for 28 species (23% of PSESP), storage characteristics are only known for 8% of PSESP (10 species). Moreover, we estimate that 60% of the listed species may require cryopreservation for long-term storage. We conclude that comparative biology studies are urgently needed on the world's most threatened taxa so that conservation action can progress beyond species listing.