Introduction

Biodiversity loss is one of the most pressing environmental issues today1,2. Globally, at least 571 plant species are considered extinct in the wild since 1750, more than twice the combined number of birds, mammals, and amphibians3. About 34% of conifers, 69% of cycads, and 70% of evaluated flowering plant species are ranked as threatened by the International Union for Conservation of Nature (IUCN, https://www.iucnredlist.org/, accessed October, 2022). Limited understanding of extinction processes will seriously hinder efforts to reverse the trend of biodiversity loss by 2030 and impede the UN’s Sustainable Development Goal 15 ‘life on land’, as global change is driving a rapid increase in ‘unpredictable’ extinctions. Therefore, clarifying spatial patterns of extinction risk and their underlying drivers is crucial for developing effective strategies to safeguard, recover, and promote the sustainable use of terrestrial ecosystems, including halting biodiversity loss1.

Extinction risk for plants has been considered to be spatially non-random and has geospatial selectivity4,5, i.e., species with similar geographical distribution ranges tend to suffer similar extinction risks6,7. Numerous comparative studies have provided insights into why some species are more vulnerable than others, linking vulnerability to extinction with specific drivers8. Extrinsic environmental factors, such as climate change, topographic heterogeneity, and anthropogenic pressures have been shown to affect population size and distribution of species8,9,10. In particular, explosive human population growth and anthropogenic environmental deterioration since the second half of the 20th century have led to significant biodiversity loss and ecosystem imbalance2,11. Recent studies suggest that vegetation structure (e.g., proportion of growth forms) and evolutionary dynamics (e.g., divergence time, diversification rate, and weighted evolutionary distinctiveness) also play crucial roles in determining threat status4,12,13,14,15. However, very few investigations have comprehensively incorporated these drivers, especially the evolutionary factors, in the assessment of extinction risks at large extents7,12 (see Fig. 1 and Supplementary Data 1 for more details on hypotheses of extinction drivers).

Fig. 1: Main hypothesized extinction drivers for flowering plants in China.
figure 1

Potential extinction drivers of flowering plants in China were divided into two categories: biodiversity-intrinsic drivers and biodiversity-extrinsic drivers. The former includes evolutionary and vegetation structure drivers, while the latter includes climatic, topographic, and anthropogenic drivers.

Previous studies across large spatial and taxonomic levels have demonstrated that threatening processes, such as specific climatic factors related to extinction risk, are scale or extent dependent11,16. For countries with high climatic and topographic heterogeneity, analysis of drivers of threatening processes has usually proven unreliable or of low predictability when treating the region as a whole16,17. This is because the stability of species’ populations is closely linked to drivers at a local scale or extent, due to regional or small-extent environmental heterogeneity16. Recognizing the indispensable role of spatial scale and/or extent effects is therefore critical in the assessment of extinction risks17 (See Supplementary Note 1 for comparison between scale and extent effects). To address this, when applied to larger spatial extents or morphologically diverse groups of taxa, studies based on multivariate analyses and incorporating scale or extent effects are needed to fully understand the spatial characteristics of extinction risk and their underlying driving forces.

China possesses highly heterogeneous topography, diverse climatic conditions, and varied ecological environments, contributing to its exceptional biodiversity and designation as one of the world’s 17 megadiverse countries (Fig. 2 and Supplementary Fig. 1). However, biodiversity in China is under threat, with a significant proportion of species at high risk of extinction18. According to the IUCN Red List criteria, ca. 11% of China’s flowering plant species had been classified as threatened based on the assessments of Chinese higher plants in 2013 and 202018,19,20. Revisions in the Red List Index reveal that the overall extinction risks for plants in China have not been alleviated21. Some studies suggest that threatened flowering plants in China are primarily affected by climate factors22 or anthropogenic influence23, or both10,24, while others suggest that the underlying drivers may be more complex25,26. Each of these studies usually focused on single drivers22,23, under-sampled specific plant clades24, or high-level taxonomic groups25. Considering the heterogeneous topography and diverse vegetation associations in China, the spatial heterogeneity of extinction risk requires examination in more detail. Key questions that remain unanswered are, how uniform are the threatening processes affecting flowering plants in China at varying spatial extents, and what are the dominant spatial-dependent drivers? Even with comprehensive assessments of environmental and evolutionary drivers, the issue of extent must still be addressed.

Fig. 2: Topography and major vegetation regions in China, highlighting spatial concentration of threatened plants.
figure 2

Black lines on the map represent boundaries of vegetation regions based on the Vegetation Regionalization Map of China, with representative photos for each region shown around the map. The blue box on the map shows the spatial concentration of threatened plants in 22–29°N and 98–110°E. A Venn diagram shows the proportion of threatened species in three spatial dimensions, with different colored circles represent the spatial distribution of threatened species in 22–29°N (green), 98–110°E (blue), and 600–1800 m (yellow), respectively. All photographs published with permission from Dan Xie (I, VI), Bing Liu (II, III, V, VII), and Limin Lu (IV, VIII). The national boundary layer was downloaded from the Standard Map Service Website (Approval Number is GS(2019)1823; http://bzdt.ch.mnr.gov.cn/browse.html?picId=%224o28b0625501ad13015501ad2bfc0256%22, accessed October 2022).

In this work, we show that potential extinction drivers for flowering plants in China are regionally complex by integrating a 27,185-taxon phylogeny and 2.02 million fine-grained distribution records in comprehensive model-based analyses. Our objectives are (1) to clarify the spatial variability of extinction risk for flowering plants in China; and (2) to identify dominant drivers for flowering plant extictions across different spatial extents to understand the critical spatial differences in extinction risk.

Results

Spatial diversity patterns of extinction risk

We assessed the autocorrelation of diversity measures of flowering plants (i.e., threatened species richness, TR; the proportion of threatened species, propTR) and potential extinction drivers using Moran’s I27. The patterns of TR and propTR were spatially similar (r = 0.75; p < 0.001), and both showed significant spatial concentration (Moran’s I (0.25, 0.49); p < 0.001) (Fig. 3a, b). Threatened species were spatially aggregated by latitude, longitude, and elevation (Fig. 3g–l). Notably, 80.9% of threatened species were concentrated in regions of 22–29°N (Figs. 3g), 81.0% in regions of 98–110°E (Figs. 3i), and 94.5% at elevations of 600–1800 m (Fig. 3k). More than 60% of threatened species were found at the intersection of the above concentrated regions, i.e., the junction of Tibet, Yunnan, and Sichuan provinces (Fig. 2).

Fig. 3: Spatial distribution patterns of different diversity measures for flowering plants in China.
figure 3

The diversity measures are threatened species richness (TR, a), proportion of threatened species (propTR, b), species richness (SR, c), endemic species richness (ER, d), phylogenetic diversity (PD, e), and phylogenetic endemism (PE, f), respectively. The significance level of the degree of spatial clustering for different diversity measures are listed after each Moran’s I. Pointplots on the right are latitudinal (g, h), longitudinal (i, j), and altitudinal patterns (k, l) of TR and propTR, respectively, with the colored bars representing values of propTR (g, i, k) and TR (h, j, l) in counties (n = 2894 counties). Points between two dotted lines in each pointplot are the core latitudinal (g, h), longitudinal (i, j), and altitudinal (k, l) regions of TR and propTR, respectively. ρ is the correlation coefficient between different measures. Colors from blue to red reflect values of different diversity measures from low to high. The national boundary layer was downloaded from the Standard Map Service Website (Approval Number is GS(2019)1823; http://bzdt.ch.mnr.gov.cn/browse.html?picId=%224o28b0625501ad13015501ad2bfc0256%22, accessed October 2022).

Phylogenetic diversity (PD) of threatened flowering plants (Supplementary Fig. 2a) exhibited a spatial pattern similar to that of PD for all flowering plants in China (Fig. 3e). Notably, regions with high PD for threatened species were predominantly located in South China, contrasting with comparatively lower PD in West and North China (Supplementary Fig. 2a). According to the standardized effective size of PD (sesPD), threatened species were phylogentically clustered in West China, while it was phylogenetically overdispersed in selected regions of East and North China, suggesting that threatened species in West China were more closely related than expected, whereas those in East and North China were more distantly related (Supplementary Fig. 2b, c).

Phylogenetic signals of extinction risk

We divided China’s landscape into eight vegetation regions and calculated Fritz’s D values to examine the phylogenetic signals in discrete variables (threatened or not) for each vegetation region. We further compared the observed D values with simulated values under the Brownian motion and random models. Our analyses showed significant phylogenetic signals of extinction risk of flowering plants within each vegetation region (D(0.681, 0.802), p0 < 0.01, p1 < 0.01; Fig. 4; Supplementary Data 2). Significantly heterogeneity has been observed for extinction risk across vegetation regions (q = 0.65, p < 0.001). Generally, the extinction risk was higher in the southern regions than in the north. The Tropical monsoon rainforests (V, see the codes in Fig. 2, hereafter) had the highest proportion of threatened species (propTR = 0.129; Fig. 4), while the Cold temperate coniferous forests (I) had the lowest (propTR = 0.020; Fig. 4).

Fig. 4: Proportions and phylogenetic signals of threatened species in different vegetation regions of China.
figure 4

The names of vegetation regions are shown in Fig. 2 and the background color represents the proportion of threatened species (dividing threatened species richness by total species richness) for each vegetation region. The simulated diagrams of phylogenetic signals of threatened species for eight vegetation regions are shown around the map, with the distribution of D values assumed to be a Brownian motion (gray) and a random model (dark gray), respectively. The red solid lines show the observed D values. p0 and p1 are p-values significantly different from the Brownian motion (D = 0; the dotted line) or random model (D = 1; the dotted line) expectation, respectively. The national boundary layer was downloaded from the Standard Map Service Website (Approval Number is GS(2019)1823; http://bzdt.ch.mnr.gov.cn/browse.html?picId=%224o28b0625501ad13015501ad2bfc0256%22, accessed October 2022).

We also divided China into three zones according to topography and climate types and calculated Fritz’s D values to further detect phylogenetic signal of extinction risks at larger extents. We found that the extinction risk of flowering plants also showed a significant phylogenetic signal within each zone (D(0.709, 0.812), p0 < 0.001, p1 < 0.001; Fig. 5) and significant heterogeneity has also been observed for extinction risk across zones (q = 0.58, p < 0.001).

Fig. 5: Phylogenetic signals, spatial threatening processes and potential extinction drivers for flowering plants in different zones based on zone-plspms.
figure 5

The map shows the spatial patterns of dominant drivers in three zones under the total effects of zone-plspms. The simulated diagrams of phylogenetic signals of threatened flowering plants for three zones are shown around the map (ac), with the distribution of D values assumed to be a Brownian motion (gray) and a random model (dark gray), respectively. Barchars in boxes (ac) show the total effects of five types of potential extinction drivers. Model name (plspmw, plspmN, and plspmS), sample size (n), value of goodness of fit (GoF), and explanatory power of threatened species (R2) for each zone are shown near the barcharts. The national boundary layer was downloaded from the Standard Map Service Website (Approval Number is GS(2019)1823; http://bzdt.ch.mnr.gov.cn/browse.html?picId=%224o28b0625501ad13015501ad2bfc0256%22, accessed October 2022).

Drivers of extinction risk at national, regional, and zone extents

The values of Moran’s I showed that all diversity measures (Moran’s I (0.16, 0.49); p < 0.001; Fig. 3a–f) and potential extinction drivers (Moran’s I (0.17, 0.69); p < 0.001; Supplementary Data 3) are spatially aggregated. These drivers involved a total of 24 variables (including six vegetation structure drivers), four evolutionary drivers, six climatic drivers, seven topographic drivers, and one anthropogenic driver in the initial partial least squares path model (plspm; see more details in ‘Methods’ section and Supplementary Dataset 1, 3). Different drivers showed varying correlations with the number of threatened species (TR, Supplementary Fig. 3) and the proportion of threatened species (propTR, Supplementary Fig. 4).

We utilized plspm to elucidate the potential pathways by which biodiversity-intrinsic and -extrinsic drivers have contributed to the extinction risks of flowering plants (i.e., extinction risks) in China and in different vegetation regions or zones, respectively. Three different levels of models, national-plspm, regional-plspms, and zone-plspms, were applied for spatial modeling. The combined effects of multiple drivers varied across plspms at national, regional, and zone levels, highlighting the need to understand all threatening processes applicable at different extents.

When China was treated as a single region, the final optimized national-plspm can account for 55.2% of the spatial extinction risk (R2 = 0.552, GoF = 0.629; Supplementary Fig. 5; Supplementary Dataset 47). The primary model of national-plspm consisted of five types of extinction drivers (latent variables) and had sufficient explanatory power (R2) for all latent variables (R2 (0.269, 0.708), Supplementary Data 4). Vegetation structures (i.e., the proportion of herbs) were identified as the dominant drivers at the national extent (negative effect standardized path coefficient, pcoef.std = −0.599, p < 0.001; Supplementary Data 6), under both the total effects (Supplementary Data 6) and direct effects (Supplementary Fig. 5). Climatic (positive effect; pcoef.std = 0.551, p < 0.001; i.e., precipitation, Prec) and evolutionary (positive effect; pcoef.std = 0.499, p < 0.001; i.e., median weighted evolutionary distinctiveness, medianWED) drivers also influenced extinction risks of flowering plants in China (Supplementary Data 6).

The regional-plspms were created to deconstruct the spatial influence of extinction risks for different vegetation regions. All regional-plspms fit very well, and their GoF values mostly meet the requirement (GoF (0.369, 0.622); Fig. 6). Overall, except for plspmVI and plspmVII, most regional-plspms can explain 25.2–53.3% of extinction risks of flowering plants at the regional level (Fig. 6 and Supplementary Dataset 811). While the extinction drivers varied across vegetation regions, some adjacent regions shared similar dominant drivers: vegetation structure drivers for Temperate deserts (VII; positive effect; pcoef.std = 0.324, p < 0.001) and Qinghai-Tibet Plateau alpine vegetations (VIII; positive effect; pcoef.std = 0.612, p < 0.001), evolutionary drivers for Temperate coniferous deciduous broad-leaved mixed forests (II; positive effect; pcoef.std = 0.484, p < 0.001), Warm temperate deciduous broad-leaved forests (III; negative effect; pcoef.std = −0.434, p < 0.001), and Temperate grasslands (VI; negative effect; pcoef.std = −0.195, p < 0.001), and climatic drivers for Subtropical evergreen broad-leaved forests (IV; positive effect; pcoef.std = 0.687, p < 0.001) and Tropical monsoon rainforests (V; positive effect; pcoef.std = 0.755, p < 0.001) (Fig. 6; Supplementary Data 11).

Fig. 6: Spatial threatening processes and potential extinction drivers of flowering plants in different vegetation regions based on regional-plspms.
figure 6

The map shows the spatial patterns of dominant driver for each vegetation region under the total effects of regional-plspms. Barchars with different colors show the total effects of five types of drivers for vegetation regions II, III, IV, V, VI, VII, and VIII, respectively. The black stars show the dominant driver for each region. Model name (plspmII–plspmVIII), sample size (n), value of goodness of fit (GoF), and explanatory power of threatened species (R2) for each vegetation region are shown above the barcharts. The national boundary layer was downloaded from the Standard Map Service Website (Approval Number is GS(2019)1823; http://bzdt.ch.mnr.gov.cn/browse.html?picId=%224o28b0625501ad13015501ad2bfc0256%22, accessed October 2022).

Dominant extinction drivers based on the well-fitted zone-plspms (GoF (0.438, 0.619), R2 (0.139, 0.543); Fig. 5) were consistent with those revealed by the regional-plspms, with vegetation structure drivers dominanting West China (including vegetations VII and VIII; negative effect; pcoef.std = −0.239, p < 0.001), evolutionary drivers dominanting North China (including vegetations II, III and VI; positive effect; pcoef.std = 0.431, p < 0.001), and climatic drivers dominanting South China (including vegetations IV and V; positive effect; pcoef.std = 0.869, p < 0.001) (Fig. 5; Supplementary Dataset 1215), further supporting spatial heterogeneity of extinction risk for flowering plants across China.

Discussion

Using a species-level phylogeny and fine-grained county-level distribution records, we find that threatened flowering plants are significantly geospatially aggregated, and the core regions are located between 22–29°N, 98–110°E, and 600–1800 m elevation (Figs. 2, 3). Spatial concentration of high extinction risk areas are in the Nyainqêntanglha Mts (36), Boshula Mts (38), Gaoligong Mts (39), Taniantaweng Mts (40), Nushan Mts (41), Yunling Mts (42) and Shaluli Mts (43), as well as in West Sichuan, including the Daxue Mts (44) and Qionglai Mts (45) (Supplementary Fig. 1). These areas contain not only the highest plant diversity and endemism, but are also recognized as evolutionary cradles in China (r (0.67, 0.90), Fig. 3d–f)28,29. There are two potential explanations for the above pattern. (1) The evolution of traits associated with extinction risks (e.g., morphology, habitat type, and chemical composition) each follows a degree of non-random evolutionary trajectories, and taxa with these traits are usually phylogenetically related and more likely to adapt to similar environmental and climatic conditions6,30. (2) Geological history theories generally assume that the spatial distribution of a species and its concordant extinction risk in southwest mountainous areas of China are mainly shaped by topographic heterogeneity9. Topographic heterogeneity within these areas has led to the formation of a variety of small, complex ecological climate and related dispersal barriers, which might have influenced gene exchange between populations and species31. When a suitable external environment appears, localized species may diverge and radiate rapidly. But species that evolve in this manner are usually specifically adapted to local environments, and most of them are naturally vulnerable to even small environmental disturbances5,9,25. Therefore, during the evolutionary process of speciation, the conservatism of specific intrinsic traits and a species’ strict requirements for complex ecological environments may both drive a concentration of species within specific ranges of latitude, longitude, and elevation32,33. These long-term aggregation processes continuously contribute to both the concentration of threatened flowering plants and their phylogenetic endemism.

We find that spatial extinction risks of flowering plants in China are driven by multiple potential drivers and are also extent dependent. At the national level, vegetation structures, represented by the proportions of herbs (R_herb) or trees (R_tree), are the direct dominant drivers of extinction risk, followed by climatic drivers (i.e., precipitation, Prec) and evolutionary drivers (i.e., median divergence time, medianDT) (Supplementary Figs. 35). While extinction drivers vary across vegetation regions, a clear geographical continuity can be observed with some adjacent regions sharing similar dominant drivers (Fig. 6). Moreover, such geographical continuity in extinction drivers has been confirmed by patterns of the zone-level analyses, with West China dominated by vegetation structure drivers, South China by climatic drivers, and North China by evolutionary drivers (Fig. 5; Supplementary Data 15).

In West China, vegetation structure represents the strongest extinction threat of many localized plant species. The proportion of herbs in this region is significantly higher than trees and shrubs (Supplementary Fig. 6), probably resulting in an imbalance in “tree-shrub-herb” ecotypes and compositional instability in most local communities, but also reflecting the adaptive potential for herbs to speciate in such environments34. These ecologically fragile ecosystems, coupled with extreme habitats, might have led to a decline in phylogenetic diversity and possibly functional diversity of local communities. In such circumstances, localized adaptation may optimize reproductive strategies while simultaneously increasing long-term extinction risk in these harsh environments. For instance, Saussurea, a genus of the family Asteraceae with a diversity center in Qinghai-Tibet Plateau alpine vegetations, maximizes resource allocation to seed production to enhance reproductive output and therefore evolutionary longevity35. However, the extremely fragile vegetation composition, dramatically changeable temperature, and long seasonal drought in West China, may make these ‘trade-offs’ in survival strategy for herbaceous flowering plants only alleviate, rather than prevent, their tendency toward extinction.

In the humid regions of South China, climatic drivers dominate the high-risk extinction of local flowering plants. The extinction risks increase with greater annual total precipitation (Prec) and average annual optimal temperature (Topti) (Supplementary Data 14). Mountainous areas (e.g., Subtropical evergreen broad-leaved forests) tend to form microclimates and unique habitats that constrain population migration and gene flow, leading to unstable populations and loss of genetic variation9,36. Furthermore, persistent global warming and increasing anthropogenic pressures are driving an upward migration and even local extinction of montane flowering plants9,37.

Another important finding is that evolutionary drivers dominate the high-risk extinction of flowering plants in North China. The flora of this region has a unique and ancient evolutionary history29 and the Changbai Mountain range has been recognized as a center of paleo-endemism28. The extinction risk of flowering plants in this region is primarily influenced by their divergence time, diversification rate, and weighted evolutionary distinctiveness. We find numerous relict plants in this region that belong to isolated lineages in the phylogenetic tree and are at high risk of extinction, including Schisandra chinensis, Caldesia parnassifolia, and Asarum sieboldii, indicating the high weighted evolutionary distinctiveness of this region. Our finding suggests that evolutionary drivers have played a significant role in promoting the spatial extinction risks of flowering plants in North China, which have been largely overlooked in previous studies24,25,38,39.

Moreover, due to the intricate nature of extinction risks and extent effect of extinction drivers, partition analyses at different levels are necessary to accurately comprehend the characteristics of individual drivers. For instance, the effects of anthropogenic drivers are almost all insignificant in the national-plspm (Supplementary Data 6) and zone-plspm (Supplementary Data 15), but are variably significant in specific vegetation regions based on regional-plspms (i.e., VIII; Supplementary Data 11). This indicates that elucidating the spatial threatened processes by treating large-extent areas as a single region cannot accurately unravel the actual state of biodiversity with highly heterogeneous extinction risks. Therefore, it is essential to divide a large area into smaller regions or zones with significant internal consistency and external disparities in vegetation characteristics.

Understanding the spatial variability of extinction risk and its underlying drivers is crucial for predicting future range shifts and extinction tendencies for extant biodiversity. In particular, identification of the spatial heterogeneity of extinction risk across different spatial extents can inform targeted and cohesive conservation and recovery strategies. Protected areas that conserve vulnerable species and significant evolutionary lineages in China should be created in a timely manner according to these spatial characteristics of extinction risk.

In the sparsely populated region of West China, extinction risk of biodiversity is dominated by vegetation structure drivers and establishing large-scale protected areas is considered appropriate. In addition to protecting ecosystem integrity and community stability, large-scale protected areas can provide windows of time and space for ecological restoration of fragile and degraded habitats. In North China, which is home to many highly evolutionarily distinct species, high-risk extinction of flowering plants is driven mainly by evolutionary drivers. To mitigate the irreversible loss of evolutionarily ancient and distinct lineages facing unpredictable extinctions, we recommend establishment of comprehensive protected areas. Much of South China is characterized by highly heterogeneous climate and topography22,37, including localized regions with high species diversity, threatened species diversity, species endemism, and phylogenetic diversity (Figs. 2, 3 and Supplementary Figs. 1, 7)28,29. Here, protection networks connected by ecological corridors should be established to promote migration among populations of species. This approach would not only preserve current living conditions of more than 80% of the Chinese human population40 but also facilitate in situ protection as much as possible.

The strong spatial heterogeneity of threatening processes on flowering plants in China calls for the development of varying conservation strategies according to the dominant threatening factors within each region. Understanding the spatial characteristics of extinction risk, and their underlying drivers, is critical to developing multidimensional conservation strategies that can link biodiversity loss and risks to the attainment of sustainable development41.

Methods

Phylogeny and extinction risk

The phylogeny used in this study was based on an existing species-level tree of life of flowering plants in China29. The original phylogeny was reconstructed by Hu et al. 42, which included 13,321 species (12,160 native to China) and 2991 genera (2743 native to China). The phylogeny was dated by Lu et al. 29. with 138 calibrations, using the penalized likelihood (PL) approach as implemented in treePL43. Complete species trees were then generated by inserting 13,864 additional species without sequence data into the randomly selected nodes below the corresponding genera of the backbone tree with the “V.PhyloMaker”44 package in R45, according to available taxonomic information. Finally, a set of complete species trees that include 27,185 species representing 2859 genera from 252 families of flowering plants native to China were generated. In this study, we selected the first complete species tree in 10_species_trees_27,185sp_s2.tre (https://doi.org/10.5061/dryad.6m905qg2w) for downstream analyses.

The IUCN Red List Categories and Criteria represent an easily and widely understood system for evaluating the threatened status of species46. We herein quantified the extinction risk of flowering plants in China according to the Red List of Higher Plants of China (https://www.mee.gov.cn/xxgk2018/xxgk/xxgk01/202305/t20230522_1030745.html)19. Species were classified as Extinct (EX), Extinct in the wild (EW), Regional extinct (RE), Critically endangered (CR), Endangered (EN), Vulnerable (VU), Near threatened (NT), Least concern (LC) and Data deficient (DD)46. Species ranked as CR, EN, and VU were considered threatened species (i.e., high-risk flowering plants in this study), which represent about 9.8% (2659 species) of the total flowering plants of China.

Distribution records

Species distribution records were obtained from two primary sources, i.e., literature and public databases. About 1.69 million county-level distribution records were obtained from Flora Republicae Popularis Sinicae (FRPS, http://www.iplant.cn/frps, accessed October, 2022), Flora of China (FOC, http://www.efloras.org/flora_page.aspx?flora_id=2, accessed October, 2022) and available regional floras (Supplementary Data 16). An additional 6.85 million collection records were obtained from the Chinese Virtual Herbarium (CVH, https://www.cvh.ac.cn/, accessed October, 2022) and the Global Biodiversity Information Facility (GBIF, https://www.gbif.org/47, accessed January, 2021). After removing invalid and duplicate records and and outliers, about 0.84 million county-level distribution records were retained in the specimen database.

We combined the literature database with the specimen database to form a comprehensive distribution database and followed the flowchart in Supplementary Fig. 8 to process the distribution records. We (1) standardized the taxonomic names of distribution records according to the checklist of native flowering plants of FOC; (2) standardized the county names of records according to codes available at http://www.mca.gov.cn/ (total number of counties: 2894); (3) combined the distribution records of infraspecific taxa into corresponding species; and (4) removed duplicate records to ensure that only one distribution record per species per county was retained. Ultimately, 2.02 million county-level distribution records were retained for further analyses. It should be noted that in addition to man-made and historical influences, the division of administrative counties in China is also closely related to environmental factors such as topography, geomorphology, and climate.

Measures of spatial diversity patterns

We defined the species diversity of flowering plants, endemic flowering plants, and threatened flowering plants in each county as species richness (SR), endemic species richness (ER), and threatened species richness (TR) for each county, respectively. The proportion of threatened species (propTR) for each county was calculated by dividing TR by SR in each county. Faith’s phylogenetic diversity (PD), defined as the total branch length spanned by the tree including all species in a local community48, was used to estimate the evolutioanry history of flowering plants in each county. We calculated the standardized effective size of PD (sesPD) using “Picante”49 package in R45 to test the phylogenetic relatedness of threatened species within counties. We generated null distributions of PD for each county by shuffling taxa labels 999 times while threatened species occurrence frequency and sampled species richness remained constant. We compared the observed PD to the mean of the null distribution by calculating a standardized effective size (sesPD) using the values of (PD-mean(null))/SD(null). Negative values of sesPD indicate phylogenetic clustering (i.e., threatened species are more closely related than expected), whereas positive values indicate phylogenetic overdispersion (i.e., threatened species are less closely related than expected). We also followed the method of Rosauer et al. to calculate phylogenetic endemism (PE) for each county by summing the valuses of PD/distribution range of a clade50.

Extinction drivers

According to the hypotheses outlined in Fig. 1 and Supplementary Data 1, the potential extinction drivers for flowering plants in China were calculated below.

Evolutionary drivers

Divergence time (DT) is the time since a species divided from its closest sister group7. We used the median divergence time (medianDT) of flowering plants in a county to measure its divergence time. Divergence time for each species was extracted from a dated phylogeny of flowering plants in China, as previous studies have revealed that it is reasonable to compare divergence times from taxon-rich regional phylogenies within regions and in a relative manner51. We used diversification rate (DR) of the terminal species, i.e., representing present-day species, to describe the geographic patterns of diversity52,53,54. We followed Jetz et al.’s method to measure the species-level lineage diversification rate (DR) for each species based on the equal-splits metric53. Specifically, it was calculated as the number of nodes that separate each species from the root of the tree weighted by the length of the branch, i.e., the distance of each node to the present53. We also defined the median diversification rate of terminal species within a county (medianDR) to measure the diversification rate of the county according to Jetz et al. 53. Evolutionary distinctiveness (ED) of a species was calculated by dividing the total PD of a clade among its members. This method can measure how isolated a species is on the phylogenetic tree55.

To obtain the weighted evolutionary distinctiveness (WED) of each species, we calculated the accumulated area of each species by dividing its area of distribution into different altitude belts at 300 meter intervals and removed unoccupied belts according to the actual altitudinal distribution of each species (Supplementary Note 2 and Supplementary Data 17). We then constrained the accumulated area of the remaining belts of each species to be its suitable geographic range size. WED (Ma/10,000 km2) refers to its ED divided by its total geographic range size54. Median weighted evolutionary distinctiveness (medianWED) of all flowering plants within a county was used to represent each county’s WED in our analyses. We calculated PE and ED in the packages of “canaper”56 and “Caper”57 in R45, respectively.

Vegetation structure drivers

In this study, all potential drivers applying to localized flowering plants that are caused by narrow ecological factors, including vegetation composition and types, are collectively referred to as vegetation structure drivers (Supplementary Data 1). We followed previous large-scale studies to define the proportions of species with different growth forms in a county to quantify regional vegetation structure58. We extracted the proportions of herbs (R_herb), trees (R_tree) and shrubs (R_shrub) of all flowering plants in each county from the datasets of Qin59 and Chen et al. 60. To avoid bias caused by incomplete sampling, the relative proportions of lianas, aquatic and epiphytic plants were not considered.

To further clarify the drivers of different vegetation structures on the extinction risks for flowering plants in China, we extracted vegetation types (vegType) and vegetation groups (vegGroup) for each county according to the 1:1,000,000 Chinese Vegetation Atlas61, which has divided China’s vegetation communities into 58 types (Supplementary Fig. 9a) and 11 groups by merging similar vegetation types (Supplementary Fig. 9b). We also merged adjacent patches of the same vegetation type together in the layer of 1:1,000,000 Chinese Vegetation Atlas to ensure that patches of the same vegetation type are not adjacent within a county61. We then defined the number of vegetation patches in the county as the degree of vegetation fragmentation (vegFrag) to quantify the fragmentation of environments facing biodiversity loss.

Climatic drivers

The datasets of average annual minimum temperature (°C), average annual maximum temperature (°C) and average annual total precipitation (mm) from the Climatic Research Unit (GRU-TS 4.03) on the platform of WorldClim 2.1 for nine years (2010–2018) were selected to quantify the impact of climate on spatial threatening processes of flowering plants62,63. Based on the three datasets described above, we first calculated annual minimum temperature (Tmin), annual maximum temperature (Tmax) and annual total precipitation (Prec) for each county, respectively. Then we defined half of the sum of Tmin and Tmax and the difference between Tmin and Tmax as the average annual optimal temperature (Topti) and the range of different temperatures (Trang) for flowering plants in each county, respectively. Finally, we extracted the average temperature vegetation dryness index (TVDI) from all pixels in each county to quantify the impact of drought on extinction risks of flowering plants (see Supplementary Data 2, Supplementary Note 2 and Supplementary Fig. 10).

Topographic drivers

Topographic drivers in this study mainly include topography and spatial location (Supplementary Data 1). We identified several potential topographic drivers based on SRTM30 digital elevation model (DEM, version 2, https://www2.jpl.nasa.gov/srtm/). We defined the average elevation (avgElev) of all sampling points in each county as the county’s elevation and the difference between the maximum elevation (maxElev) and the minimum elevation (minElev) as the county’s elevation variation (variElev) (Supplementary Note 2). The degree of surface roughness in a county was defined as topographic roughness (topoRough) (Supplementary Fig. 11). We also used the longitude (Long) and latitude (Lat) of the geometric center of each county to represent the spatial locality of each species within that county.

Anthropogenic driver

In this study, the global human footprint was selected to measure direct impact of anthropogenic effects on flowering plants of China (Supplementary Data 1 and Supplementary Fig. 12)64. The county-level human footprint (HFP) was extracted from the global human footprint database (https://doi.org/10.5061/dryad.052q5) according to the county-level boundaries.

Phylogenetic signals

Fritz’s D statistic was used to measure phylogenetic signals of extinction risks for flowering plants in China (threatened were marked with 1 and otherwise with 0)65,66 among vegetation regions and zones, respectively. We used phylo.D function in R package “caper”57 to calculate Fritz’s D value, which compares the sum of changes in estimated nodal values of a binary trait (threatened or not) along branches of the phylogeny against the random and Brownian expectations. D = 1 suggests that the trait (threatened or not) has evolved randomly with respect to the phylogeny, and D > 1 suggests that the trait is more overdispersed than the random expectation. D = 0 indicates that the trait has evolved following the Brownian model, and D < 0 indicates that the trait is more phylogenetically conserved than the Brownian expectation. D (0, 1) indicates a gradient of possible scenarios between pure Brownian and pure random evolution65. Two p-values are further calculated based on the simulations with 999 permutations, where p1 (D < 1) and p0 (D > 0) respectively indicate the probability of the D value of the binary trait resulting from a random or Brownian phylogenetic structure. We reported the exact values of Fritz’s D statistic directly, as categorizing the strength of a phylogenetic signal as strong, moderate, or weak is considered subjective and contentious66.

Spatial analyses

To test whether the spatial extinction risks of flowering plants within the same region are more similar than those among regions, we used the q statistic to quantify the degree and significance of spatial heterogeneity for different diversity measures. The value of q ranges from −1 to 1; the larger the q is, the more significant the spatial heterogeneity is67.

To reduce the inconvenience and bias caused by numerous factors, we used two analyses to filter extra factors in the modeling. The modified t-test in the “SpatialPack” package of R68 was used to check the spatial consistency between diversity measures (i.e., TR and propTR) and potential extinction drivers (r). The value of r, ranges from −1 to 1, was used to quantify the degree of spatial consistency; and the larger the r is, the higher the spatial consistency of biodiversity measures is68. The Moran’s I was used to examine the spatial autocorrelation of diversity measures (i.e., TR and propTR) and potential extinction drivers, respectively. The value of I ranges from −1 to 1. The closer I is to 1 (high z-scores and appropriate p value), the more clustered the spatial distribution of a diversity measure is; the closer I is to −1, the more discrete the measure is; the closer I is to 0, the more random the measure is27.

Spatial modeling

Plspm (partial least squares path model) has been widely used to assess complicated environmental impacts in studies such as species richness, ecological environment, agri-tourism and sustainability69,70,71. In this study, plspm was used to investigate how biodiversity-intrinsic and -extrinsic factors have contributed to the spatial extinction risks of flowering plants (propTR) in China at varying spatial extents. The latent variables in our plspms here included evolution, climate, topography, vegetation and anthropogenic effects. Generally, the nested phylogenetic relationships between clades should be taken into consideration in models that treated extinction risks of evolutionary clades as the response variables. However, in our spatial threatened modeling, the response variables were the extinction risks of flowering plants of different geographic units, rather than extinction risks of different evolutionary clades. Nested phylogenetic relationships between clades were taken into a consideration when we quantified potential evolutionary drivers (i.e., medianDT, medianDR, and medianWED). The values of these evolutionary drivers with nested phylogenetic relationships of each geographic unit was calculated and mapped into corresponding units in each layer as a type of spatial driver prior to modeling. Therefore, it was not necessary to consider the nested phylogenetic relationships of clades again in the modeling. This spatial mapping method of evolutionary properties has been applied in many biodiversity conservation studies12,54.

Several steps are necessary in spatial modeling (Supplementary Data 7). Variable detection. If the potential driver has an important influence on a diversity measure, the spatial pattern should also be similar to this measure27,67. We identified potential drivers by Moran’s I of spatial autocorrelation and removed the randomly distributed drivers. Variable standardization and null value processing. All potential drivers (measured variables) were divided into five types: evolutionary, climatic, topographic, anthropogenic, and vegetation structure drivers (Fig. 1, Supplementary Fig. 13, and Supplementary Dataset 1, 3). Null values of some original layers were estimated by the random forest prediction method provided by the “MISSFOREST” package in R72. Spatial model construction. We designed a metamodel containing five types of extinction drivers (latent variables), whose inner model and outer model consisted of the latent variables and extinction risk (such as TR) and the latent variables and their relevant specific factors, respectively (Supplementary Fig. 13). In plspm, each latent variable could include one or more manifest variables. The path coefficients represented the directions and strength of relationships among latent variables, and the explained variability (R2) was also estimated.

To explore potential drivers of extinction risk for flowering plants in China, a region with high climatic and topographic heterogeneity, and to elucidate the extent-dependent characteristics of extinction risk, we constructed three sets of models tailored to different spatial extents: national-plspm for the whole of China, regional-plspms for the vegetation regions, and zone-plspms for zones. We first constructed a national-plspm to explain the spatial extinction risk (propTR, hereafter) affecting all flowering plants in China based on the metamodel (Supplementary Fig. 13). Due to the significant heterogeneity of extinction risk for flowering plants, we then divided China into eight distinct regions (Fig. 2) based on the Vegetation Regionalization Map of China (1: 6,000,000) (from Resources and Environmental Sciences and Data Center, http://www.resdc.cn/, accessed October, 2022). We then constructed eight regional-plspms to explain the spatial extinction risks of flowering plants for each vegetation region (Supplementary Data 2). The plspmII, plspmIII, plspmIV, plspmV, plspmVI, plspmVII, and plspmVIII were names of models for the eight vegetation regions. The model for Cold temperate coniferous forests (plspmI) cannot be implemented because it does not meet the requirement of a minimum sample size ( > 30). We further constructed three zone-plspms by dividing China into three zones, West China, North China, and South China, according to precipitation, climate types and incorporating vegetation boundaries, to further test whether spatial extinction risks of flowering plants in China are extent-dependent. The plspmW, plspmN, and plspmS were names of models for three zones, i.e., West China, North China, and South China, respectively.

We then evaluated the reliability of all models by verifying the one-dimensionality of latent variables, the validity of inner and outer models, and the significance of path coefficients (representing the direction and strength of relationships between latent variables) of different models based on a bootstrap resampling. Lastly, we continuously optimized these models until these parameters meet the requirements (Supplementary Note 3 and Supplementary Data 7). The construction and verification of each model was conducted using the “plspm” package in R (9999 bootstraps)73.

Reporting summary

Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.