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Genetic diversity is a critical resource for species’ survival during times of environmental change. Conserving and sustainably managing genetic diversity requires understanding the distribution and amount of genetic diversity (in situ and ex situ) across multiple species. This paper focuses on three emblematic and IUCN Red List threatened oaks (Quercus, Fagaceae), a highly speciose tree genus that contains numerous rare species and poses challenges for ex situ conservation. We compare the genetic diversity of three rare oak species—Quercus georgiana, Q. oglethorpensis, and Q. boyntonii—to common oaks, investigate the correlation of range size, population size, and the abiotic environment with genetic diversity within and among populations in situ, and test how well genetic diversity preserved in botanic gardens correlates with geographic range size. Our main findings are: (1) these three rare species generally have lower genetic diversity than more abundant oaks, (2) in some cases, small population size and geographic range correlate with genetic diversity and differentiation, and (3) genetic diversity currently protected in botanic gardens is inadequately predicted by geographic range size and number of samples preserved, suggesting non-random sampling of populations for conservation collections. Our results highlight that most populations of these three rare oaks have managed to avoid severe genetic erosion, but their small size will likely necessitate genetic management going forward.

Tissue culture using mature-phase plant material is a useful tool for species conservation, but can be a challenge with oak (Quercus) species, often resulting in low growth and survival. Two different tissue culture media were compared and used to determine whether there was a survival, growth, or contamination response pattern in species representing three North American oak taxonomic sections: red oaks (section Lobatae), white oaks (section Quercus), and golden oaks (section Protobalanus). Mature phase cuttings were harvested in springtime from 12 oak species: arkansas oak (Q. arkansana), canby oak (Q. canbyi), slender oak (Q. graciliformis), nuttall oak (Q. texana), boynton sand post oak (Q. boyntonii), california scrub oak (Q. dumosa), engelmann oak (Q. engelmannii), gambel oak (Q. gambelii), canyon live oak (Q. chrysolepis), palmer oak (Q. palmeri), island oak (Q. tomentella), and huckleberry oak (Q. vacciniifolia). Excised shoot-tip explants were placed onto either Lloyd and McCown woody plant (WP) medium or Gresshoff and Doy (GD) medium. More growth responses and longer survival times were seen on explants grown on the WP medium than GD medium. Explants originating from species native to xeric habitats or those with smooth, glabrous young leaves had significantly higher contamination rates. Although no significant differences were found when grouped by taxonomic section, survival, growth, and contamination varied significantly by species. These findings contribute to the process of establishing tissue culture methods using mature oak material, particularly in relation to medium selection and sterilization protocols, which is critical to the conservation of this iconic group of species.

Genetic diversity provides the essential basis for the adaptation and resilience of tree species to environmental stress and change. The genetic conservation of tree species is an urgent global necessity as forest conversion and fragmentation continue apace, damaging insects and pathogens are transported between continents, and climate change alters local habitat suitability. Effective and efficient genetic conservation of tree species presents a substantial challenge because of the lack of basic information about many species, inadequate resources, and a historical lack of coordination within and between conservation sectors. Several cooperative efforts are already under way and are achieving conservation success, but much work remains. The Gene Conservation of Tree Species—Banking on the Future workshop in 2016 enabled the exchange of information and the creation of collaborations among tree conservation stakeholders. Several key themes emerged during the meeting’s presentations and dialogue, which are further explored in this paper. In situ conservation of species is the long-term goal and is often the most efficient approach for preserving the genetic diversity of many forest tree species. Whether existing reserves adequately protect species and are sufficient for future conservation needs is uncertain. Ex situ conservation is an important complement to in situ efforts, acting as an insurance measure against extinction, providing material for restoration, enabling additional research opportunities, and educating the public. Networks of botanic gardens, government agencies, and non-governmental organizations must continue to coordinate ex situ and in situ efforts to improve the efficiency and effectiveness of tree conservation efforts. Assessing and prioritizing which species and populations require genetic conservation and prioritizing among them is a critical need. Two key tree restoration needs are for wider dissemination of planting stock, particularly stock with resistance to insects and pathogens, and for specific silvicultural prescriptions that facilitate restoration efforts. Effective genetic conservation of forest trees will require ongoing cooperation among widely diverse groups of scientists, managers, and policymakers from the public and private sectors.

Effectively conserving biodiversity with limited resources requires scientifically informed and efficient strategies. Guidance is particularly needed on how many living plants are necessary to conserve a threshold level of genetic diversity inex situcollections. We investigated this question for 11 taxa across five genera. In this first study analysing and optimizingex situgenetic diversity across multiple genera, we found that the percentage of extant genetic diversity currently conserved varies among taxa from 40% to 95%. Most taxa are well below genetic conservation targets. Resampling datasets showed that ideal collection sizes vary widely even within a genus: one taxon typically required at least 50% more individuals than another (thoughQuercuswas an exception). Still, across taxa, the minimum collection size to achieve genetic conservation goals is within one order of magnitude. Current collections are also suboptimal: they could remain the same size yet capture twice the genetic diversity with an improved sampling design. We term this deficiency the ‘genetic conservation gap’. Lastly, we show that minimum collection sizes are influenced by collection priorities regarding the genetic diversity target. In summary, current collections are insufficient (not reaching targets) and suboptimal (not efficiently designed), and we show how improvements can be made.

With 10% of trees (> 8,000 species) threatened with extinction there is an urgent need for botanical gardens to protect threatened trees in dedicated conservation collections. Species conservation is mentioned in the mission statements of most major botanical gardens, yet the actual conservation value of existing ex situ tree collections is low. We conducted interviews with members of the botanical garden community and organized a symposium at the 5th Global Botanic Gardens Congress to identify challenges and collect recommendations to improve living ex situ tree collections. We summarize and evaluate this information to facilitate gardens becoming more effective agents for global tree conservation. Experts agree that gardens offer valuable strengths and assets for tree conservation. Some challenges exist, however, including a lack of strategic conservation focus, collection management limitations, gaps in fundamental biological information for trees, and a lack of global coordination. Solutions are offered to facilitate gardens and arboreta of all sizes to participate more effectively in tree conservation. Prioritizing genetically diverse tree collections, participating in conservation networks, developing tree-specific conservation models and guidelines, and strengthening tree science research efforts are a few examples. Most importantly, a more coordinated global effort is needed to fill knowledge gaps, share information, and build conservation capacity in biodiversity hotspots to prevent the loss of tree species.

Diverse forms of nanoscale architecture generate structural colour and perform signalling functions within and between species. Structural colour is the result of the interference of light from approximately regular periodic structures; some structural disorder is, however, inevitable in biological organisms. Is this disorder functional and subject to evolutionary selection, or is it simply an unavoidable outcome of biological developmental processes? Here we show that disordered nanostructures enable flowers to produce visual signals that are salient to bees. These disordered nanostructures (identified in most major lineages of angiosperms) have distinct anatomies but convergent optical properties; they all produce angle-dependent scattered light, predominantly at short wavelengths (ultraviolet and blue). We manufactured artificial flowers with nanoscale structures that possessed tailored levels of disorder in order to investigate how foraging bumblebees respond to this optical effect. We conclude that floral nanostructures have evolved, on multiple independent occasions, an effective degree of relative spatial disorder that generates a photonic signature that is highly salient to insect pollinators. Disordered nanoscale striations on petals, tepals and bracts have evolved multiple times among flowering plants and provide a salient visual signal to foraging bumblebees (Bombus terrestris). The natural world is always a bit fuzzy at the edges, but the fuzziness has a purpose. The surfaces of petals of many flowers have striations or ridges, which scatter light. But these arrays of ridges are not always arranged in a regimental order. In this paper, Beverley Glover and colleagues find that all of the flowering plants that they examined whose petals have such striations always display the same degree of disorder. This creates a 'blue halo' around the petals that pollinators find attractive. The authors find that similarly disorderly conduct happens in all flowering plants that are pollinated by insects or other animals, whereas the most primitive flowers, which are not pollinated by animals, seem not to have this capacity for orderly disorder.

Montane cloud forests (MCFs), with their isolated nature, offer excellent opportunities to study the long-term effects of habitat fragmentation and the impacts of climate change. Quercus arbutifolia is a rare oak in MCFs of southern China and Vietnam. Its isolated populations, small population size and unique ecological niche make this species vulnerable to climate change and habitat loss. In this study, we used chloroplast (cpDNA) and nuclear (ITS) DNA sequences to investigate genetic divergence patterns and demographic history of five of the six known populations of Q. arbutifolia. Considering its small population size and fragmentation, Q. arbutifolia has unexpectedly high genetic diversity. The time since the most recent common ancestor of all cpDNA haplotypes was c. 10.25 Ma, and the rapid diversification of haplotypes occurred during the Quaternary. The maximum clade credibility chronogram of cpDNA haplotypes suggests that the DM population (Daming Mountain, Guangxi province) diverged early and rapidly became isolated from other populations. The Pearl River drainage system may have been the main geographic barrier between DM and other populations since the late Miocene. ITS data suggests that population expansion occurred during the last interglacial of the Quaternary. The combined effects of pre-Quaternary and Quaternary climatic and geological changes were the main drivers to the current genetic diversity and distribution pattern of Q. arbutifolia. Because of the high between-population genetic differentiation and high within-population genetic diversity of Q. arbutifolia, conservation efforts should be implemented for all populations, but if conservation resources are limited, populations DM, YZ (Mang Mountain, Hunan province) and ZZ (Daqin Mountain, Fujian province) should have priority.

Historical geoclimatic events have shaped the distribution patterns and intraspecific divergence of plants. Numerous phylogeographical studies in China have focused on the Qinghai-Tibetan Plateau and surrounding areas due to the complex topography and high species diversity, but the impact of Neogene events and Quaternary climatic change on the flora of subtropical China remains poorly understood. Quercus glauca, a widespread tree of East Asian subtropical evergreen forests, has rich fossil records dating back to the Neogene, and it provides a good model to explore the impact of paleogeoclimate changes on East Asian subtropical forests. We used three chloroplast DNA (cpDNA) intergenic spacer regions and ecological niche modeling (ENM) to analyze the divergence pattern and demographic history of Q. glauca in China and Japan. A total of 33 haplotypes were detected. The phylogenetic analysis revealed two major haplotype lineages (Southwest China vs. Southeast China and East China Sea). The limited dispersal ability of seeds and complex topography resulted in the high total, inter- and intrapopulation haplotype diversity. The fossil-constrained BEAST analysis revealed a lineage diversification in the late Miocene-Pliocene. The formation of complex topography changes since Miocene in east Himalaya and adjacent area might be the key factor that triggered the intraspecific divergence of Q. glauca. Haplotype spatial distribution, ENM, mismatch distribution, and neutrality tests suggest that Q. glauca in Southeast China experiences expansion, and the current distribution in region III might be shaped by southward expansion from regions I and II after last glacial maximum (LGM). Regions I and II were the potential glacial refugia of Q. glauca.