Southeast Asia (SEA) has seen strong climatic oscillations and fluctuations in sea levels during the Quaternary. The impact of past climate changes on the evolution and distribution of local flora in SEA is still poorly understood. Here we aim to infer how the Quaternary climate change affects the evolutionary process and range shifts in two pine species. We investigated the population genetic structure and diversity using cytoplasmic DNA markers, and performed ecological niche modeling to reconstruct the species past distribution and to project range shift under future climates. We found substantial gene flow across the continuous distribution of the subtropical Pinus yunnanensis. In contrast, the tropical Pinus kesiya showed a strong population structure in accordance with its disjunct distribution across montane islands in Indochina and the Philippines. A broad hybrid zone of the two species occurs in southern Yunnan. Asymmetric introgression from the two species was detected in this zone with dominant mitochondrial gene flow from P. yunnanensis and chloroplast gene flow from P. kesiya. The observed population structure suggests a typical postglaciation expansion in P. yunnanensis, and a glacial expansion and interglacial contraction in P. kesiya. Ecological niche modeling supports the inferred demographic history and predicts a decrease in range size for P. kesiya under future climates. Our results suggest that tropical pine species in SEA have undergone evolutionary trajectories different from high latitude species related to their Quaternary climate histories. We also illustrate the need for urgent conservation actions in this fragmented landscape.

China has the most numerous Danxia and Karst landscapes, which serve as special terrestrial islands harboring ample endemic species, though how did these endemic species spread among those isolated sites is still an unresolved issue. To address this question, we explored the phylogeographical structure and demographic history of Firmiana danxiaensis, a tree species endemic to Danxia and Karst landscapes. We collected 295 samples (28 populations) of F. danxiaensis. Plastid genomes were assembled for 25 representative samples. Sanger sequencing of four plastid regions and restriction-site-associated DNA sequencing were performed on the 28 populations. The phylogenetic tree constructed from plastid genomes and restriction site-associated DNA sequencing (RAD-seq) data supported that F. danxiaensis originated from Mount Danxia and Nanxiong Basin, spread to Karst landscapes near Yingde City, and then back to Danxia Mountain and the Nanxiong Basin. In the Nanxiong Basin, the latter arrivals captured the plastid of the former. Population analyses revealed strong population structure among and within Danxia and Karst landscapes, possibly due to low seed and pollen dispersal abilities of the species. The demographic and ecological niche modeling approaches suggested that F. danxiaensis have widely occurred in the southeast of China during the last glacial period, and later retreated to the cliffs of Danxia and Karst landscapes due to temperature rising and competition failure. The declining of the effective population size of the species throughout the postglacial period suggested that global warming, agriculture, and industrial civilizations could have affected the survival of this species, and more measures should be taken to conserve these species.

The discontinuous geographic distribution pattern of plants in the north temperate zone has been a focus of biogeographic research, especially concerning the mechanisms behind the formation of such a pattern and the spatial and temporal evolution of this intermittent distribution pattern. Hypotheses of boreotropical origin, land bridge migration, and out-of-Tibet have been proposed to explain the formation of the discontinuous distribution pattern. The distribution of Lonicera shows a typical Europe–Asia–North America discontinuous distribution, which makes for a good case study to investigate the above three hypotheses. In this study, we inferred the phylogeny based on plastid genomes and a nuclear data set with broad taxon sampling, covering 83 species representing two subgenera and four sections. Both nuclear and plastid phylogenetic analyses found section Isika polyphyletic, while sections Nintooa, Isoxylosteum, and Coelxylosteum were monophyletic in subgenus Chamaecerasus. Based on the nuclear and chloroplast phylogeny, we suggest transferring Lonicera maximowiczii and Lonicera tangutica into section Nintooa. Reconstruction of ancestral areas suggests that Lonicera originated in the Qinghai–Tibetan Plateau (QTP) and/or Asia, and subsequently dispersed to other regions. The aridification of the Asian interior may have facilitated the rapid radiation of Lonicera in the region. At the same time, the uplifts of the Tibetan Plateau appear to have triggered the spread and recent rapid diversification of the genus on the QTP and adjacent areas. Overall, our results deepen the understanding of the evolutionary diversification history of Lonicera.

Clear species boundaries are crucial for plans and actions on biodiversity conservation. However, morphological similarities among allied species can result in taxonomic difficulties, thus impeding conservation efforts. In China, Cinnamomum japonicum Siebold is a well-known endangered plant, yet suffers from longstanding taxonomic issues. Here, we explicitly evaluate whether C. japonicum, C. chenii, and C. chekiangense are the same phylogenetic species on the basis of a multi-individual sampling strategy. We identified three sets of low-copy orthologous genes from 19 Lauraceae taxa for phylogenetic inferences. Both the concatenation and coalescent-based phylogenies supported that C. chenii individuals were embedded in the C. japonicum clade, indicating these two taxa are conspecific. Meanwhile, C. chekiangense accessions formed a monophyly which was not sister to C. japonicum. This result, together with the morphological differences that the leaves of C. japonicum are glabrous with a faveolate pattern of venation while those of C. chekiangense have trichomes and inevident lateral veins, led us to consider both as two distinct species. Based on 17 728 neutral single nucleotide polymorphisms (SNPs), the ADMIXTURE analysis suggested that the Chinese C. japonicum populations in Zhoushan Archipelago (=C. chenii) were genetically differentiated from the Japanese and Korean ones. Furthermore, ecological niche modeling predicted that the present distribution area of Chinese C. japonicum is likely to be unsuitable under global warming scenarios. Together with its limited distribution and genetic uniqueness, we recommend that Chinese C. japonicum deserves conservation priorities.

The classification of species in the genus Pterocyclus has been a topic of concern, as they were initially considered members of Pleurospermum (Apiaceae) in the Flora of China. However, the intergeneric and infrageneric classifications of Pterocyclus and its allies, such as Hymenidium and Pleurospermum, have been controversial. To address these issues, we performed phylogenetic analyses using one nuclear marker (nrITS) from 167 accessions, including 137 species (including five species of Pterocyclus), and 105 plastid genes from 82 accessions representing 82 species (including five species of Pterocyclus) of Apiaceae. We used both maximum likelihood and Bayesian approaches to deduce phylogenetic relationships of Pterocyclus and its allies. Furthermore, we conducted morphometric analyses that specifically targeted the mericarp morphology, and compared the structural differences in their plastid genomes. Based on these findings, we suggest the following revisions to the classification of Pterocyclus and its allies: (i) Pterocyclus should encompass five species (Pterocyclus angelicoides, Pterocyclus forrestii, Pterocyclus rotundatus, Pterocyclus tibeticus, and Pterocyclus wolffianus), all of which are all monophyletic and placed in the Komarovieae; (ii) Pterocyclus rivulorum shows both phylogenetic and mericarp morphological similarities to Hymenidium apiolens and Hymenidium dentatum, which belongs to the Hymenidium Clade, thus we provisionally transfer it to Hymenidium; (iii) Pleurospermum longicarpum is considered conspecific with Pterocyclus angelicoides based on morphological descriptions in the Flora Xizangica; (iv) we describe and illustrate Pterocyclus tibeticus as a new species; and (v) Pterocyclus wolffianus should be recognized as a valid species and not considered a synonym of Pterocyclus forrestii.

The genus Impatiens comprises more than 1000 species and displays enormous morphological diversity. As a taxon that is notoriously difficult to classify morphologically, the taxonomic significance of pollen morphology has been discussed in previous studies. However, there was only limited study on the evolution of palynological and macroscopic character in this genus before. In this paper, we observed pollen of 143 species of Impatiens, including all representatives of infrageneric groups and discussed their taxonomic value. Meanwhile, based on the reconstructed phylogenetic framework, we selected five pollen traits, and nine macroscopic traits including both vegetative and reproductive organs for evolutionary analysis. The character reconstruction showed that the morphology and number of aperture, granules in lumina, seed number of per capsule, number of sepals, lateral united petals connate, spur length, and phyllotaxy could be identified as unambiguous, while other characters were ambiguous in the last common ancestor of Impatiens. The results of comprehensively macroscopic characters and palynological evidence suggest that these traits experienced a complicated evolution, exhibit high levels of instability and variability and occur character multiple reversals in the evolutionary processes of Impatiens due to different selection pressures. In addition, we found that there is an evident mosaic evolution in this genus. Pollen and macroscopic character are conserved with a slower evolutionary rate in the I. subgen. Clavicarpa, however, these characters showed higher diversity with a rapid rate of evolution in the I. subgen. Impatiens. Furthermore, the relationship between floral morphology and pollinators was discussed.

Hybrid genomes usually harbor asymmetrical parental contributions. However, it is challenging to infer the functional significance of asymmetrical retention of parental alleles in hybrid populations of conifer trees. Here we investigated the diversity in the glutathione S-transferase (GST) gene family in a hybrid pine Pinus densata and its parents (Pinus tabuliformis and Pinus yunnanensis). Plant GSTs play major roles in protecting plants against biotic and abiotic stresses. In this study, 19 orthologous groups of GST genes were identified and cloned from these three species. We examined their expression in different tissues, and then purified the corresponding proteins to characterize their enzymatic activities and specificities toward different substrates. We found that among the 19 GST orthologous groups, divergence in gene expression and in enzymatic activities toward different substrates was prevalent. P. densata preferentially retained P. yunnanensis-like GSTs for 17 out of the 19 gene loci. We determined the first GST crystal structure from conifer species at a resolution of 2.19 Å. Based on this structure, we performed site-directed mutagenesis to replace amino acid residuals in different wild-types of GSTs to understand their functional impacts. Reciprocal replacement of amino acid residuals in native GSTs of P. densata and P. tabuliformis demonstrated significant changes in enzyme functions and identified key sites controlling GSTs activities. This study illustrates an approach to evaluating the functional significance of sequence variations in conifer genomes. Our study also sheds light on plausible mechanisms for controlling the selective retention of parental alleles in the P. densata genome.

Phylogenomics enhances our understanding of plant radiations in the biodiverse Andes. Our study focuses on Puya, primarily Andean and a part of the Bromeliaceae family. Using a phylogenomic framework based on the Angiosperms353 probe set for 80 species, we explored Puya′s phenotypic evolution and biogeography. Divergence time analyses and ancestral area estimations suggested that Puya originated in Central Coastal Chile around 9 million years ago (Ma). Subsequently, it dispersed to the dry valleys of the Central Andes and Puna regions between 5–8 Ma, leading to the emergence of major lineages. Key events in the last 2–4 million years include the recolonization of Chilean lowlands and dispersal to the northern Andes via Peru's Jalcas, facilitating passage through the Huancabamba depression. This event gave rise to the high-elevation Northern Andes clade. Using phylogenetic comparative methods, we tested the hypothesis that adaptation to the Andes' island-like high-elevation ecosystems was facilitated by unique leaf and floral traits, life history, and inflorescence morphology. Our findings suggest correlations between inflorescence axis compression, protective bract overlap, and high-elevation living, potentially preventing reproductive structure freezing. Semelparity evolved exclusively at high elevations, although its precise adaptive value remains uncertain. Our framework offers insights into Andean evolution, highlighting that lineages adapted to life in dry ecosystems can easily transition to high-elevation biomes. It also underscores how the island-like nature of high-elevation ecosystems influences phenotypic evolution rates. Moreover, it opens avenues to explore genetic mechanisms underlying adaptation to extreme mountain conditions.

Scots pine (Pinus sylvestris L.) is one of the most important tree species of the temperate and boreal zones in Eurasia. Its wide distribution range and current patterns of genetic variation have been influenced by Quaternary climatic oscillations and the demographic processes connected to them. In order to better understand the relationship between evolutionary history and demographic factors in a widespread species with a large genome, we used the single-nucleotide polymorphism (SNP) array to genotype thousands of SNP markers across 62 natural populations (N = 686 trees) of Scots pine in Eurasia. This provides the largest range-wide SNPs' genetic diversity assessment of Scots pine to date. Our findings show evidence of past admixture events between genetic clusters that were retained despite the potential for effective pollen-mediated gene flow across the species' distribution range. We also examined the contemporary population structure of the species and analyzed the range-wide genetic diversity patterns. Phylogenetic analyses and demographic modeling suggest that the observed divergence patterns between genetic lineages likely predate the last glaciation events. Two of the most distinctive groups are represented by trees from the eastern parts of Fennoscandia and Eastern Russia, which have remained separated since the mid-Pleistocene. The patterns of genetic variation also confirm the dual colonization of Fennoscandia and the existence of an admixture zone in Central Europe that was formed during multiple waves of postglacial recolonization. This study provides insights into the genetic relationships of Scots pine populations from Europe and Asia and offers a more comprehensive understanding of the species' history.

Chinese Tajiks are an Indo-Iranian-speaking population in Xinjiang, northwest China. Although the complex demographic history has been characterized, the ancestral sources and genetic admixture of Indo-Iranian-speaking groups in this region remain poorly understood. We here provide the genome-wide genotyping data for over 700 000 single-nucleotide polymorphisms (SNPs) and mtDNA multiplex sequencing data in 64 Chinese male Tajik individuals from two dialect groups, Wakhi and Selekur. We applied principal component analysis (PCA), ADMIXTURE, f-statistics, treemix, qpWave/qpAdm, Admixture-induced Linkage Disequilibrium for Evolutionary Relationships (ALDER), and Fst analyses to infer a fine-scale population genetic structure and admixture history. Our results reveal that Chinese Tajiks showed the closest affinity and similar genetic admixture pattern with ancient Xinjiang populations, especially Xinjiang samples in the historical era. Chinese Tajiks also have gene flow from European and Neolithic Iran farmers-related populations. We observed a genetic substructure in the two Tajik dialect groups. The Selekur-speaking group who lived in the county had more gene flow from East Asians than Wakhi-speaking people who inhabited the village. These results document the population movements contributed to the influx of diverse ancestries in the Xinjiang region.

Polyploids are common in Camellia sect. Paracamellia, which contain many important oil crop species. However, their complex evolutionary history is largely unclear. In this study, 22 transcriptomes and 19 plastomes of related species of Camellia were sequenced and assembled, providing the most completed taxa sampling of Camellia sect. Oleifera and C. sect. Paracamellia. Phylogenetic trees were reconstructed with predicted single-copy nuclear genes and plastomes. Phylogenetic trees with nuclear genes demonstrated that C. sect. Oleifera should be merged into C. sect. Paracamellia. Cytonuclear discordance and network analyses suggested hybridizations among polyploid species and relatives. The divergence of major clades in C. sect. Paracamellia was dated to be during the middle to late Miocene from the ancestral Lingnan region, and a rapid diversification during the Quaternary was found, probably through hybridization and polyploidization. The tetraploid Camellia meiocarpa Hu may have originated from hybridization between closely related diploid species. The hexaploid Camellia oleifera C. Abel probably originated from hybridization between closely related diploid and tetraploid (e.g., C. meiocarpa) species. The octoploid Camellia vietnamensis T. C. Huang ex Hu could have originated from hybridization between hexaploid C. oleifera and the closely related diploid species. Hybridization and polyploidization played an important role in generating the rich variation of important fruit traits, especially increased fruit size in polyploid species.

Habitat stability is important for maintaining biodiversity by preventing species extinction, but this stability is being challenged by climate change. The tropical alpine ecosystem is currently one of the ecosystems most threatened by global warming, and the flora close to the permanent snow line is at high risk of extinction. The tropical alpine ecosystem, found in South and Central America, Malesia and Papuasia, Africa, and Hawaii, is of relatively young evolutionary age, and it has been exposed to changing climates since its origin, particularly during the Pleistocene. Estimating habitat loss and gain between the Last Glacial Maximum (LGM) and the present allows us to relate current biodiversity to past changes in climate and habitat stability. In order to do so, (i) we developed a unifying climate-based delimitation of tropical alpine regions across continents, and (ii) we used this delimitation to assess the degree of habitat stability, that is, the overlap of suitable areas between the LGM and the present, in different tropical alpine regions. Finally, we discuss the link between habitat stability and tropical alpine plant diversity. Our climate-based delimitation approach can be easily applied to other ecosystems using our developed code, facilitating macro-comparative studies of habitat dynamics through time.

Transposable elements (TEs) are prevalent components of diverse genomes, and play an important role on the genomic stability and expression regulation of their adjacent genes. It is interesting to know the variation of TE expression and the effects of the presence/absence of TEs on gene expression after hybridization. Here we assessed the expression variation of TEs and the impacts of TEs on expression of nearby genes after hybridization based on comparisons of three pairs of reciprocal F₁ hybrids and four parents in Capsella rubella. Of the 480 TE families expressed in all the four parents and six F₁ hybrids, 7–23 (1.5%–4.2%) TE families were significantly differentially expressed between in silico and real F₁ hybrids, indicating the expression levels of these TE families were affected during hybridization. In particular, there was a Copia TE superfamily and a non-long terminal repeat (non-LTR) TE differentially expressed between the reciprocal F₁ hybrids of 879 and 86IT1, indicating maternal effects may have impacts on expression of TEs in these F₁ hybrids. Besides the impacts on the expression of TE families of the hybridization, genes adjacent to polymorphic TEs tended to show a higher proportion (24.83%) of allele-specific expression (ASE) in F₁ hybrids. Overall, our results highlight the impacts of hybridization on the expression level variation of TEs, and the effects of TEs on ASE after hybridization.

The big-bracted dogwood clade Benthamidia of Cornus is a typical example of the well-known eastern Asia (EA) and North America (NA) floristic disjunction, with greater species diversity in EA than in NA. The lineage provides an opportunity to explore factors contributing to the plant diversity unevenness between EA and NA and test hypotheses on the origin of disjunct distribution from a phylogenetic perspective. We generated RAD-seq data, conducted phylogenomic and biogeographic analyses for the clade with sampling of all species (9) and subspecies (10) currently recognized in floras. We also assessed species delineation and calculated phylogenetic diversity to evaluate the diversity unevenness between EA and NA. Finally, we examined variation of diversification rates and ecological niches on the phylogeny to explore potential causes underlying the observed diversity pattern. Our results revealed phylogenetic relationships congruent with previous studies and suggested a trans-Beringian ancestral distribution of the clade Benthamidia in the mid-Oligocene, dispersal from Mexico to eastern United States in the mid-Miocene, and early diversification of the EA clade in SW China. Our results also confirmed greater phylogenetic diversity and diversification rate of the EA clade. Species delimitation analysis suggested 17 species in the clade Benthamidia, including all recognized subspecies. By integrating the results of molecular data with morphology, we proposed to retain the subspecies without changing their ranks. Our data suggested increased diversification rate in EA as an intrinsic factor explaining the greater species diversity in the region driven mainly by biogeographic isolation and partially by niche divergence.

The fern genus Didymoglossum (Hymenophyllaceae) is not so diverse in Africa with seven species at most. However, its local taxonomy is surprisingly still strongly debated, in particular within the Didymoglossum erosum complex interpreted either as a single polymorphic species or as a group of at least three distinct but morphologically very close taxa (D. erosum, Didymoglossum chamaedrys, and Didymoglossum benlii). Investigating these taxonomic issues and more generally the diversity of the genus in Africa and its origin, we conducted a complete anatomo–morphological analysis coupled with a molecular phylogenetic work based on rbcL. Our results support the recognition of all seven species, including Didymoglossum robinsonii that is likely distinct from the Neotropical Didymoglossum reptans to which the African populations were traditionally attributed. We here propose new characters and a novel key to distinguish the seven African species which also include Didymoglossum ballardianum, Didymoglossum lenormandii, and Didymoglossum liberiense. Once the taxonomy is clarified with respect to the distinct evolutionary lineages evidenced, the biogeographic history of the genus in Africa is discussed based on a divergence time estimation and the reconstruction of the ancestral geographic areas. These analyses reveal a Mesozoic (Cretaceous) vicariance event within Didymoglossum which is the second one hypothesized for the family Hymenophyllaceae.

Phylogenetics is crucial in the study of evolutionary processes and events transpiring in the course of species diversification. Phylogenetic studies within kingdom Plantae often reveal hybridization and introgression. Here, we study a subsection rife with historic hybridization and discuss the impacts of such processes on evolutionary trajectories. Aliciella subsection Subnuda comprises seven species of herbaceous plants occurring in Utah, the Navajo Nation, and the Four Corners region of North America. Previous molecular and morphological work left relationships in the subsection unresolved. Here, we use comparative DNA sequencing of nuclear ITS and chloroplast DNA regions and genome-wide RAD-seq data to clarify phylogenetic relationships and examine the role of hybridization in the subsection. We construct haplotype and nucleotype networks from chloroplast and nuclear ITS sequence matrices and compare nuclear and chloroplast phylogenies to identify multiple putative chloroplast capture events. The RAD-seq maximum likelihood phylogeny and multispecies coalescent species tree robustly resolve relationships between six species-level clades. We use STRUCTURE and HyDe on the RAD-seq data to evaluate the influence of hybridization within the subsection. The HyDe results suggest that hybridization has occurred among all species in the subsection at some point in their history. Cytonuclear discordance reveals historic chloroplast capture, and we discuss potential causes of the observed discordance. Our study robustly resolves relationships in Aliciella subsection Subnuda and provides a framework for discussing its speciation despite a history of hybridization and introgression.

A fundamental question in speciation genomics is how evolutionary processes shape the genomic landscape of differentiation between species. Regions of elevated differentiation, referred to as genomic islands, could be shared among closely related species (shared islands) or specific to a lineage (lineage-specific islands). Shared islands are typically assumed to result from background selection. However, simulations and empirical studies have suggested that positive selection contributes to both shared and lineage-specific islands. Here, we utilized comparative population genomics to examine the contributions of different evolutionary processes to patterns of genetic differentiation when gene flow and incomplete lineage sorting are minimal. We used whole-genome resequencing data for 135 individuals from four oak species, including two independent species pairs, Quercus variabilis Blume and Quercus acutissima Carruth. in the subgenus Cerris, and Quercus dentata Thunb. and Quercus griffithii Hook.f. & Thomson ex Miq. in the subgenus Quercus. We found that both shared and subgenus-specific islands were caused by positive selection, including selective sweeps in current populations and in their most recent common ancestors. Moreover, the recombination rate was a better predictor of genomic differentiation than gene density. Overall, our results reveal that recombination and positive selection impacted genomic differentiation considerably and provide a more precise grasp of how genomic islands formed in Quercus.

Obtaining reliable species identification of the legume genus Caragana has been challenging. Until now, species identification was mostly carried out utilizing diagnostic morphological characteristics, in addition to some successful applications of secondary chemical compounds. This study was designed to establish a DNA barcoding protocol enabling unambiguous identification of 238 accessions belonging to 67 species of Caragana. The performance of four DNA barcoding regions nrITS, trnH-psbA, matK, and rbcL was explored using three analytical approaches, Pairwise Genetic Distance, Sequence Similarity and Phylogenetic Tree method. The chloroplast regions rbcL and matK showed lower discriminatory power compared with the nuclear region internal transcribed spacer (ITS) and the chloroplast region trnH-psbA. The nrITS outperformed the other regions in the resolution rate. The present study brings forth an efficient barcode locus for Caragana. A barcode based either on a single-locus nrITS or the combination of nrITS and trnH-psbA was found to be most suitable for species discrimination with distinctive barcoding gaps. An attempt has also been made to resolve taxonomic issues in the Caragana opulens complex. DNA barcoding tools when complemented with alpha taxonomic evidence can aid in solving complex systematic problems, especially when taxa are characterized by overlapping traits, such as species belonging to the Fabaceae family.

Rhododendron is the largest genus in Ericaceae and is well known for its diversity and beauty of flowers present in different species, making it a much-revered lineage of ornamental plants. Many species of Rhododendron are intolerant of high temperatures, which are becoming more common and intense in urban areas under global climate change. Therefore, the discovery and description of genes from heat-tolerant Rhododendron lineages are essential in the development of new climate-resilient cultivars. One such species known to be heat tolerant is Rhododendron × pulchrum Sweet. To better understand the genomics of heat tolerance in this species, we assembled a haplotype-resolved and chromosome-scale genome for R. × pulchrum, which had a genome size of 509 Mb; a scaffold N50 of 37 251 370 bp; and contained 35 610 genes. In addition, based on the same reannotation pipeline, we conducted pan-genomic analyses for all seven available chromosome-scale Rhododendron genomes and found 14 415 gene groups shared across all species and 18 018 gene groups distributed in the other species, including 1879 gene groups found in only a single species. Finally, we analyzed the transcriptomic data from heat-treated and non-heat-treated R. × pulchrum plants to quantify the genes that are most important during heat stress in an effort to inform the development of climate-resilient cultivars. This study provides insight into the genome diversity in Rhododendron and targets several genes related to agronomic traits that may help in further analysis.

Having a comprehensive understanding of genetic differentiation, responses to environmental change and demographic history is critical for genetic improvement and conservation efforts. Forest trees are an excellent resource for understanding population differentiation and adaptive genetic variation due to their ability to adapt to different climates and environments. Cephalotaxus oliveri is a relict conifer endemic to China. In this study, we generated transcriptome data and identified 17 728 high-quality single-nucleotide polymorphisms (SNPs) from 18 populations. We found significant negative correlations between expression diversity and nucleotide diversity within and among populations, suggesting that gene expression and nucleotide diversity have a reciprocal relationship when the species adapts to the environment. The analyses of population structure showed that C. oliveri displayed a striking genetic structure with four groups. BayeScEnv and RDA methods detected the signatures of local adaptation, and identified that 738 outlier SNPs were associated with precipitation, temperature and soil conditions across heterogeneous environmental conditions. Approximate Bayesian computation analyses showed that the first and second divergence occurred in the late Miocene (c. 10.075 million years ago [Ma]) and the middle Pleistocene transition (c. 0.815 Ma), respectively. Ecological niche modeling of C. oliveri revealed signs of westward expansion after the last glacial maximum, while it was predicted to experience significant range contractions in future climate change scenarios. Geographical factors and environmental factors in southern China have played a critical role in establishing the current genetic diversity and population structure of C. oliveri. This study provides an important reference for forest resource management and conservation for C. oliveri.

The general dynamic model (GDM) of oceanic island biogeography views oceanic islands predominantly as sinks rather than sources of dispersing lineages. To test this, we conducted a biogeographic analysis of a highly successful insular plant taxon, Cyrtandra, and inferred the directionality of dispersal and founder events throughout the four biogeographical units of the Indo-Australian Archipelago (IAA), namely Sunda, Wallacea, Philippines, and Sahul. Sunda was recovered as the major source area, followed by Wallacea, a system of oceanic islands. The relatively high number of events originating from Wallacea is attributed to its central location in the IAA and its complex geological history selecting for increased dispersibility. We also tested if diversification dynamics in Cyrtandra follow predictions of adaptive radiation, which is the dominant process as per the GDM. Diversification dynamics of dispersing lineages of Cyrtandra in the Southeast Asian grade showed early bursts followed by a plateau, which is consistent with adaptive radiation. We did not detect signals of diversity-dependent diversification, and this is attributed to Southeast Asian cyrtandras occupying various niche spaces, evident by their wide morphological range in habit and floral characters. The Pacific clade, which arrived at the immaturity phase of the Pacific Islands, showed diversification dynamics predicted by the island immaturity speciation pulse model (IISP), wherein rates increase exponentially, and their morphological range is controlled by the least action effect favoring woodiness and fleshy fruits. Our study provides a first step toward a framework for investigating diversification dynamics as predicted by the GDM in highly successful insular taxa.

Despite representing a fraction of the global terrestrial surface area, oceanic islands are disproportionately diverse in species, resulting from high rates of endemicity. Island plants are thought to share a unique phenotype—referred to as an island syndrome—which is thought to be driven by convergent evolution in response to selection by shared abiotic and biotic factors. One aspect of the island plant syndrome that has received relatively little research focus is that island plants are expected to have converged on conservative resource use associated with slow growth rates and weak competitive abilities. Here we tested whether native, woody Hawaiian plant species are phenotypically distinct—with more resource-conservative leaf traits—compared to a globally distributed sample of continental species. Using an archipelago-wide trait data set, we detected that on average, native Hawaiian species had lower leaf nutrient concentrations overall, and lower nutrient concentrations at high leaf mass per area, but no other phenotypic differences compared with continental plants. There was also considerable overlap in the trait spaces of native Hawaiian species and continental species. Our findings indicate that an island plant syndrome for leaf traits is not present in the Hawaiian flora, and that island species can demonstrate extensive variation in their resource-use strategies, on a scale that is comparable with that of continental species worldwide.

Climate change is promoting global declines in plant diversity, which are expected to be more critical in islands or island-like ecosystems due to environmental constraints and isolation. The species' vulnerability to climate change (VUL) depends on their ability to cope with changes or mitigate them. Therefore, we investigate the influence of growth and dispersal strategies of species from the Sugarloaf Rock Complex, Brazil, an island-like ecosystem, on their niche breadth (NB), long-dispersal (LD) capacity, and geographical range (GR). Besides, we evaluate the potential use of these strategies as indicators of species' VUL. We found that rock specialists exhibit narrower NB, lower LD capacity, and a more restricted GR when compared to other species. We also found that 63% of rock specialists are found in conservation red-lists and they are more vulnerable to climate change than woody plants. Conversely, self-dispersed plants are expected to be less vulnerable to climate change when compared to species with other dispersal mechanisms. Species vulnerable to climate change are 14 times more likely to be included in conservation red lists, and it might indicate that the species' VUL might also describe the species' vulnerability to other anthropogenic threats. Still, we suggest conservation attention on some species that are expected to be vulnerable to climate change but were not yet included in conservation red lists. We advocate for more efforts to ensure the conservation aspects of different functional groups in which inselbergs might not only offer isolation but also a refuge opportunity.

Interspecific trait divergence may reflect adaptation and reproductive isolation, particularly after the rapid differentiation that may follow the colonization of new environments. Although new lineages are generally expected to be morphologically and ecologically similar to their ancestors, environmental forces can also drive adaptive differentiation along specific phenotypic axes. We used climate niche models and comparative analyses based on a previously inferred phylogeny to examine the history of ecological and morphological divergence of Neotropical firs (Abies Mill., Pinaceae), a group of conifers that have recently colonized and diversified in the mountains of Mexico and northern Central America. We inferred past secondary contact zones by comparing current and past climate niche projections and looked for evidence of recent interspecific gene flow using genomic data. Neotropical firs have similar niches to each other and show a strong phylogenetic signal for most evaluated morphological traits. Analyses based on individual variables suggested a random walk model of differentiation. However, early adaptation to tropical conditions is inferred in the ancestor of the southernmost firs, as all modern southern taxa are differentiated climatically from Abies concolor, the northernmost species. In addition, observed autapomorphic traits for soil properties and the number of resin ducts in needles are consistent with possible species-specific adaptations. Thus, a combination of nonadaptive and adaptive processes along different phenotypic axes, some related to the environment, likely operated after the southward migration of this plant lineage from North America and its subsequent radiation in the Neotropics.

Newly investigated leafy twigs bearing axillary fruits from the Eocene Parachute Creek Member of the Green River Formation in eastern Utah, USA, have provided more information on the species previously attributed to the Proteaceae as Banksia comptonifolia R.W.Br. The leaves are simple, estipulate with short petioles, and elongate laminae with prominent angular nonglandular teeth. The laminae have a thick midvein and pinnate craspedodromous secondaries, and are distinctive in the presence of a thick, often coalified, marginal rim. Vegetative and reproductive buds occur in the axils of the leaves. These features indicate that the species belongs to Palibinia Korovin—an extinct Eudicot genus previously known only from the Paleogene of Asia and Europe. Small pedicellate ovoid fruits 1.5–2.2 mm wide are borne in fascicles of three and are seen to be capsules with four apical valves. Despite the specific epithet referring to similarity of the foliage to that of Comptonia (Myricaceae), the fasciculate inflorescence organization with axillary flowers is quite distinct from the catkins characteristic of that family. Assignment to Banksia or other Proteaceae with complex inflorescences and follicular fruits is also problematic. Additionally, MacGinitie′s transfer of the species to Vauquelinia of the Rosaceae is contradicted by the lack of stipule scars on the twig and by differences in leaf venation and floral morphology. We transfer the species to Palibinia comptonifolia (R.W.Br.) comb. nov., but its familial affinity within the Pentapetalae remains uncertain. This new occurrence augments records from the Paleogene of Turkmenistan, Kazakhstan, China, England, and Germany.

Quantifying the relative strength of isolating barriers is a major focus of research on plant speciation. Contrasting life histories and mating systems have the potential to limit gene exchange between closely related populations growing in sympatry. However, few studies have quantified reproductive isolating barriers between conspecific annual and perennial populations and their contributions to total reproductive isolation (RI). Incarvillea sinensis Lam. (Bignoniaceae) is an insect-pollinated herb with largely allopatric annual and perennial populations that differ in mating systems. The perennial populations are primarily outcrossing whereas annual populations are predominantly selfing. At a rare sympatric site in northern China we estimated prezygotic and postzygotic barriers to gene exchange between annual and perennial plants and found complete RI between the two life histories. Annuals exhibited significantly higher ecogeographic isolation than perennials whereas perennials experienced more isolation through pollen–pistil interactions than annuals. Crosses between annuals and perennials demonstrated that postzygotic barriers influencing fruit and seed formation, F₁ germination and survival were negligible for annuals but played a small role for perennials. However, F₁ hybrids of crosses between annuals and perennials produced no pollen and their ovules were largely sterile. Our study provides insight into the relative importance of prezygotic and postzygotic isolating barriers between closely related annual and perennial populations of I. sinensis and some of these barriers could have been involved with speciation. Annuals and perennials of I. sinensis represent two biological species and thus deserve to be recognized as distinct taxonomic species.

The adaptive significance of phenotypic differences between females and males can provide insights into sex-specific selection and the evolution of sexual dimorphism. Dioecious plants commonly exhibit sexual dimorphism in height, although its ecological and evolutionary significance have rarely been examined experimentally. Here, we investigate the functional consequences of the temporal reversal of height dimorphism for pollen and seed dispersal in dioecious Rumex hastatulus Baldw., a species in which males are taller than females at flowering and the reverse pattern occurs at fruiting. Populations of this colonizing weed are wind-pollinated and seeds are wind-dispersed. In a glasshouse experiment we manipulated the height of pollen donors and using sex-specific genetic markers compared the paternal success of males of contrasting height and investigated whether seed families showed evidence of sexual dimorphism in early life-history traits. In a second glasshouse experiment using fruiting plants we also examined how female height influenced the distance that seeds were dispersed. We found that taller males had significantly higher siring success than males of equivalent height to flowering females. Similarly, taller females dispersed fruit to greater distances than shorter females. Female seeds were significantly heavier than male seeds and germinated more rapidly, although early seedling growth was greater in males. Our study suggests that the striking sex reversal of height in R. hastatulus likely functions to optimize the contrasting reproductive functions of the sexes by promoting increased pollen and seed dispersal distances. Improved dispersal quality could limit inbreeding and reduce local mate and resource competition within populations.

Islands in the tropical Pacific Ocean are renowned for high biodiversity and endemism despite having relatively small landmasses. However, our knowledge of how this biodiversity is formed remains limited. The taxon cycle, where well-dispersed, earlier colonizers become displaced from coastal to inland habitats by new waves of colonizers, producing isolated, range-restricted species, has been proposed to explain current biodiversity patterns. Here, we integrate the outcomes of phylogenetic studies in the region to investigate the sources, age, number of colonizations, and diversification of 16 archipelagos in the tropical and subtropical South Pacific. We then evaluate whether the results support the taxon cycle as a plausible mechanism for these observations. We find that most species in the Pacific arrived less than 5 Mya from geographically close sources, suggesting that colonization by new taxa is a frequent and ongoing process. Therefore, our findings are broadly consistent with the theory of the Taxon Cycle, which posits that ongoing colonization results in the gradual displacement of established lineages. Only the oldest archipelagos, New Caledonia and Fiji, do not conform to this trend, having proportionally less recent colonization events, suggesting that the taxon cycle may slow on older islands. This conclusion is further validated by New Caledonia having lower diversification rate estimates than younger islands. We found that diversification rates across archipelagos are negatively correlated with area and age. Therefore, a taxon cycle that slows with island age appears to be a suitable concept for understanding the dynamic nature and biodiversity patterns of the Pacific Islands.

Tsuga (hemlock) is a small genus of 10 extant species in the Pinaceae, with a disjunct distribution in East Asia and eastern and western North America. Reliable species-level identification of Tsuga fossils depends on the discovery of seed cones with intact bracts, but such cones are rare in the fossil record. Here we describe a new fossil species of hemlock as T. weichangensis sp. nov. based on exquisitely preserved seed cones with nearly complete bracts from the Lower Miocene of Weichang, Hebei Province, North China. This fossil species displays a mosaic of characters between Tsuga and Nothotsuga. The well-developed and slightly exserted bract scales of T. weichangensis are reminiscent of Nothotsuga, but other characters, such as nonleaved peduncles and tongue-shaped bract scales, in addition to monosaccate pollen found at the same fossil locality, suggest an affinity closer to Tsuga. Cladistic analysis based on 15 morphological characters and a molecular backbone constraint supports the assignment of these fossil cones to Tsuga rather than Nothotsuga, and places the fossil species of T. weichangensis in an unresolved polytomy within the genus Tsuga. The occurrence of Tsuga seed cone fossils indicate the paleoclimate in the Miocene of Weichang was warmer and more humid than today's climate, which is consistent with the paleoclimate reconstructed by paleopalynology.