The Liuqu Formation in southern Tibet, China, archives the late Palaeocene Liuqu flora (ca. 56 Ma) and represents ancient vegetation on the northern margin of the Indian Plate near the India–Asia collision zone. It therefore provides critical evidence for evaluating early biotic interactions between India and Eurasia. Here, we report on Syzygium (Myrtaceae) fossil leaves from the Liuqu flora. Detailed morphological comparisons suggest that these specimens represent a new fossil species, namely Syzygium ovatum Y. Gao et T. Su sp. nov. By integrating fossil records with deep-time ecological niche modelling, we infer that Syzygium originated on the Indian Plate before or during the Palaeocene. By the middle Eocene, Syzygium had migrated to the northeast along the Asian Pacific coastline to East Asia, consistent with an “Out-of-India” dispersal scenario. Fossil evidence demonstrates that the genus reached New Zealand and Australia by the Early Miocene, likely through a Southeast Asian dispersal corridor. During the Pliocene, the distribution of Syzygium resembled that of its modern range. Although the African fossil record of Syzygium only dates to the early Pliocene, climatic suitability and favourable paleogeographic conditions suggest an earlier arrival: 1) during the Palaeocene via the Kohistan–Ladakh Island Arc and associated island systems or 2) during the Oligocene, when more suitable areas for Syzygium linked Africa and India. Generally, our results suggest a Palaeocene origin of Syzygium on the Indian Plate instead of an early Eocene Australian origin as previously proposed.

Polyploidy is an important evolutionary force increasing plant diversity and environmental resilience. Reconstructing genome size (GS) and ploidy of plant fossils advances our understanding of plant evolution and stress adaptation. Palaeopolyploidy is usually inferred from molecular data, but precise timing of polyploidy events requires improvement. So far there has been no robust fossil evidence for palaeopolyploidy in angiosperms. Here, the GS of late Eocene (similar to 34.6 Ma, the Markam flora) and Middle Miocene (similar to 15 Ma, the Namling flora) sclerophyllous oak (Quercus sect. Heterobalanus) fossils from southern Tibet, and three Late Pliocene fossils from Yunnan, China, were derived using the strong positive correlation between guard cell length (GCL) and GS. The estimated GS of the Namling fossils was approximately double those of late Eocene and Late Pliocene fossils as well as extant samples, indicating that the Namling fossils probably experienced a polyploidisation event. These tetraploids seemingly conferred greater resilience to aridity and cold-induced stress after similar to 15 Ma, reflected by two distinct fossil assemblages preserved in this flora, coincident with uplift of the Gangdese. Our discovery of sclerophyllous oak tetraploids provides compelling fossil evidence for palaeopolyploids in angiosperms, and demonstrates plant adaptation at the genome level to regional climatic change triggered by mountain uplift. GCL analysis serves as a promising tool for investigating GS changes across land plant evolution. Future research of elucidating the drivers of GCL variation is essential for enhancing the precision and reliability of this proxy.

Wildfire exerts significant influences on ecosystem succession, carbon cycles, and climate evolution; therefore, understanding the history of wildfire and its forcing factors in the geological past is of great importance. However, most paleofire records are confined to the Last Deglaciation (after 19 cal kyr BP), with few from earlier periods, hindering understanding of long-term spatiotemporal patterns of regional wildfire and climate. In this study, we reconstruct the relationship between wildfire and climate in southwestern China from similar to 33 to 14 cal kyr BP by analyzing polycyclic aromatic hydrocarbons (PAHs), organic carbon isotopes (delta C-13(org)), and geochemical elements from the Xujiaba (XJB) peatland on the Ailao Mountains in Yunnan Province. Our findings indicate that, on orbital timescales, wildfire activity increased from similar to 33 to 18 cal kyr BP and then decreased after that. Wildfire frequency was higher during Marine Isotope Stage (MIS) 2 than MIS 3. Cross-wavelet transform analysis reveals that wildfire activity was primarily driven by fluctuations in precipitation. Furthermore, by comparing paleofire records from central-eastern and southeastern China, we found an asynchronous pattern of wildfire activity in southern China during the Last Glacial Maximum (LGM). This pattern may be linked to regional hydroclimate heterogeneity between southwestern and central-eastern/southeastern China resulting from a weakened Asian monsoon and El Ni & ntilde;o-Southern Oscillation (ENSO) variability. This study provides important insights for understanding large-scale wildfire patterns, as well as forcing factors, during the LGM.

Premise of study. Davidia involucrata Baill. (Nyssaceae) is considered a "living fossil" species, with a natural distribution in the mountains of southwestern and central China presently, but its historical distribution is still unclear because of limited fossil records. This study reported Davidia endocarp fossils in appreciable numbers from the early Eocene (similar to 55-52 Ma) sedimentary sequence of India, comprising the first fossil record of this genus in South Asia. Methodology. We determined the studied fossils' taxonomic position based on their detailed morphological features in comparison to modern and fossil endocarps of Cornales. The paleoclimate conditions of Davidia were quantitatively reconstructed using the coexistence approach. Pivotal results. These fossil specimens, characterized by vertically and laterally compressed ellipsoid to obovoid endocarps; five to eight prominent, external, longitudinal, and meridianal ribs; five to seven elliptical locules; and the presence of fibers at the inner endocarp wall, are described as a new species, namely, Davidia indica A. Ali, T. Su et M. A. Khan sp. nov. Conclusions. This discovery supports the close biogeographic lineage between India and other parts of the Northern Hemisphere. This discovery suggests that, like other "living fossil" species, Davidia had a much wider ecological niche in the geological past than it has in the present day, emphasizing the need for further studies regarding the factors in shaping its modern restricted distribution.

Vegetation rarely responds instantaneously to meteorological variations; instead, its adjustment often reflects delayed and accumulated climatic influences. However, these temporal effects have not been comprehensively analyzed at the global scale, particularly with higher-resolution Earth Observation (EO) data and across multiple climate drivers. By leveraging EO datasets and modeling approaches, this study characterizes global trends in vegetation and climate, evaluates time effects, and develops climate–vegetation regression and prediction models. Our results revealed normalized difference vegetation index (NDVI) increase alongside shifts in key climatic variables during the study period. A large proportion of vegetated regions showed temporal responses, with heterogeneity in major climate zones. Incorporating time-effect variables into eXtreme Gradient Boosting (XGBoost) model influenced model performance across regions, while temperature (Tmp) and surface solar radiation downwards (SSRD), together with their corresponding temporal-effect predictors, were identified as the key influential climatic contributors. Among predictive approaches, Long Short-Term Memory (LSTM) showed the highest skill in capturing nonlinear vegetation–climate interactions. These findings underscore that temporal effects are fundamental to global vegetation dynamics and point to the need for EO-based, multivariable modeling frameworks to elucidate ecosystem response under ongoing climate change.

The discovery of fossilised blossoms resembling those of the Australian endemic genus Backhousia Hook. & Harv. (Backhousieae: Myrtoideae: Myrtaceae), in the Eocene sediments (Palana Formation; similar to 55-52 Ma) of the Gurha lignite mine, Rajasthan, India, constitute the first fossil record of Backhousia outside Australia. The taxonomic placement of the fossils was evaluated using a total evidence approach, combining morphological and molecular data in a single matrix to reconstruct phylogenetic relationships. Detailed macromorphological traits were documented and compared with both modern and fossil species of Myrtaceae. The Eocene specimens are characterised by laterally impressed, vertically flattened, long pedicellate, actinomorphic, epigynous flowers with a perianth of five sepals, a gynoecium having a globose inferior summit-domed ovary, a single long style, a capitate stigma, and a thickened cup-shaped hypanthium with a circular nectary at the crest. These fossils point to an ancient Gondwanan presence for Backhousia and may represent a significant biogeographic link back to the time when India and Australia separated in the Cretaceous.

The biodiverse forests of southern Indochina face severe anthropogenic pressure, but understanding of their deep-time history remains limited due to the general lack of fossil evidence. Here, we present a new Plio-Pleistocene macrofossil flora from the ing 565 specimens of 44 morphotypes. The assemblage is dominated by dicotyledonous leaves with well-preserved venation or cuticles and is characterized by entiremargined leaves (with only one toothed morphotype) and relatively small leaf sizes (87% microphylls and notophylls). The flora, in rank order, has abundant Syzygium paceae) leaves, along with potential representatives from Fabaceae, Lauraceae, Phyllanthaceae, and Lecythidaceae. Both leaf physiognomy and floristic composition indicate that the Kon Tum flora represents a lowland seasonal tropical broad-leaved forest linked to extant regional forests. The diverse associated palynoflora supports this paleovegetation interpretation with mixed source environments and indicates a Pliocene to early Pleistocene age of deposition in a coastal, fluvial setting with tidal influence. The study site is currently at an elevation of over 500 m, indicating significant uplift since deposition. This study marks the first Cenozoic paleobotanical collection of southern Indochina and presents an ancient analog of the extant regional lowland monsoon forests, one of the world's most threatened forest ecosystems.

Eastern Northwest China (ENC) has experienced pronounced warming and drying, while recent precipitation changes call for a refined understanding of summer drought evolution. This study classifies summer drought (SD) into persistent drought (PD) and episodic drought (ED) based on the temporal evolution of the 3-month Standardized Precipitation Evapotranspiration Index (SPEI-3), and investigates their spatiotemporal characteristics, atmospheric drivers, and oceanic precursors. PD exhibits spatially coherent, season-long negative SPEI-3 anomalies, whereas ED shows a pronounced non-drought-to-drought transition, evolving from near-normal or wet conditions in June to drought in July-August. Although PD and ED affect broadly similar regions, they differ fundamentally in their temporal evolution, indicating that temporal variability provides a more robust basis for classification than spatial patterns alone. PD is maintained by a stable Eurasian wave train and persistent moisture divergence, while ED arises from an intraseasonal circulation shift marked by the weakening and eastward retreat of the western Pacific subtropical high (WPSH), turning moisture conditions from convergence to divergence. Distinct sea surface temperature (SST) precursors further discriminate the two types: PD is linked to a persistent South Indian Ocean Dipole (SIOD), whereas ED is preceded by the tropical North Pacific meridional mode (TNP). In contrast, the conventional SD category is often associated with the transition from La Nina in the preceding winter to El Nino, without distinguishing between persistent and episodic drought evolution. Overall, the persistence and evolution of regional SST anomalies, rather than ENSO background conditions alone, are key to distinguishing drought types in ENC. Monitoring regional SST persistence can extend predictive lead time and improve subseasonal-to-seasonal drought prediction.

The species-rich Polistes Latreille, 1802 is the only cosmopolitan genus among social wasps. In contrast to its extant high diversity and wide distribution, its fossil record is sparse and geographically limited, especially in Asia. Here, we report the discovery of a new species, Polistes tibetensis Xu, Carpenter & Somavilla, sp. nov. from the Upper Eocene Niubao Formation (similar to 39 Ma), in Tibet, documented based on both male and female specimens. It represents both the oldest Polistes and the oldest Polistinae fossil record in Asian deposits to date. It could be confidently assigned to the subgenus Polistes (Polistes) based on cladistic analysis. As a confirmed crown-group fossil, P. tibetensis is expected to refine the temporal calibration of the phylogenetic tree of Polistes. Combining these findings with paleoecological niche modeling suggests that the paleoclimate of Xiede site around 39 Ma was characterized by cold winters and high seasonality. Thus, the discovery of these new fossils could provide insights into the divergence time of crown-Polistes, as well as shed light on the paleoclimate and paleoecology of the central Tibetan Plateau at that time.

Fossil wood from the Late Miocene of Manchar Formation in the Lower Indus Basin, the Sindh Province, Pakistan has been attributed to Terminalioxylon sp. (cf. T. eo-olivari Harsh, Sharma & Suthar) (Combretaceae). This is the first fossil evidence of this family from the Manchar Formation, exposed in the Lower Indus Basin. Terminalioxylon sp. (cf. T. eo-olivari) is characterised by the combination of the lack of growth rings, small to large intervessel pits, abundant aliform and aliform-confluent axial parenchyma, the lack of septate fibres, exclusively uniseriate rays, and the occurrence of prismatic crystals in ray cells. The mesomorphic wood traits, including vessels (75-173 mu m in tangential diameter, 6.4-7.2 per mm2) and abundant axial parenchyma, suggest that T. sp. (cf. T. eo-olivari) might be a large tropical or subtropical forest tree species. This fossil wood species provides new evidence for the forest vegetation in what is now Sindh Province during the Late Miocene. Forests predated the expansion of grassland, which occurred about 8 Mya in this region, due to global cooling and local aridification after the Middle Miocene Climatic Optimum.

Fossil leaves from the early Eocene sediments (similar to 55-52 Ma; Palana Formation) of Gurha Lignite Mine, Rajasthan, western India, provide a valuable window into ancient plant-insect associations, offering critical insights into trophic interactions within tropical rainforests of India during the early Cenozoic. A systematic analysis of insectmediated foliar damage was conducted on fossil leaves representing thirteen plant families. Damage types (DTs) were identified and classified into five major functional feeding groups (FFGs). The frequency and diversity of damage were quantified to reconstruct the nature of plant-insect interactions and infer palaeoenvironmental conditions. Fifty-four distinct DTs were documented, indicating interactions with at least four insect orders: Coleoptera, Blattodea, Hemiptera, and Hymenoptera. Within the early Eocene Rajasthan flora, hole feeding (29.4%) represents the most prevalent feeding strategy, whereas skeletonization (2.9%) is the least common across different plant families. When viewed in a broader palaeolatitudinal context, the Palana assemblage exhibits patterns consistent with the latitudinal herbivory hypothesis, showing higher frequencies and a greater diversity of specialized damage types (e.g., galls, mines, and polylobate holes) than contemporaneous higherlatitude floras. These patterns indicate complex and specialized plant-insect interactions consistent with sustained warm and humid conditions in western India during the early Eocene. By filling a major geographic gap in the early Eocene herbivory record, this study provides a valuable baseline for comparing trophic interactions across palaeoenvironments and enhances our understanding of how climatic signals shaped the plant-insect relationships during the early Eocene hothouse.

Premise of research. Fabaceae fossil leaf records are abundant, but their identification within the family is challenging because of the lack of distinctive leaf architecture in many genera. Sindora (Fabaceae, Detarioideae, Detarieae) is a genus of paleotropical trees distributed mainly in Southeast Asia. Previous macrofossil records are limited to questionable leaves and woods. We report fossil leaflets with diagnostic characters of Sindora in a newly discovered early Pleistocene flora from Kon Tum, central Vietnam. Methodology. We collected 37 fossil fabaceous leaflets from the Kon Tum Formation at the Hung Phat site in Kon Tum City, Quang Ngai Province, Central Highlands region of Vietnam. Leaf architecture was compared with extant species by consulting digitized herbarium collections and the literature. Pivotal results. Diagnostic characters of the fossil leaflets include the pulvinulate petiolule, retuse to emarginate apex, wavy margin, convex to cuneate base, curved midvein, craspedodromous or semicraspedodromous secondary venation, and subapical midvein gland. The geologically recent age, morphological similarity, and overlapping ex tant and fossil distributions with extant S. siamensis all support assignment to Sindora cf. S. siamensis. Conclusions. The new specimens represent the first unequivocal macrofossil record for Sindora, confirming the genus's presence in Indochinese forests by the early Pleistocene. As the first deciduous taxon recognized in the Kon Tum flora, the Sindora cf. S. siamensis occurrence supports a monsoonal regional climate, as found today. The con trast between the fossil abundance and current endangered status of S. siamensis in Vietnam provides paleobotanical insights for conservation planning.

Fossil records of Fagaceae have been widely reported in the Northern Hemisphere including many findings from East Asia. However, the history of their diversification within tropical Asia remains poorly understood, primarily constrained by the paucity of relevant fossil records from this region. In this study, we report well-preserved fossil leaves of Quercus section Cyclobalanopsis from the late Oligocene to Early Miocene of the Li Basin, northern Thailand. This new record comprises leaves with an acuminate apex, serrate margin (half-toothed in upper part of lamina), craspedodromous secondaries in the toothed part, opposite or alternate percurrent intercostal tertiary, anomocytic stomata and unicellular trichomes on abaxial epidermis. We assign these fossil leaves to a new species, Quercus liensis N. Thongsangtum, J. Huang et T. Su nov. sp., belonging to Quercus section Cyclobalanopsis. Detailed morphological comparisons indicate that the nearest living relative (NLR) of Q. liensis nov. sp. is most closely allied with Q. shennongii, a species currently distributed in the subtropical regions of southeastern China. In conjunction with previous palynological studies, this discovery suggests that a subtropical evergreen broad-leaved forest dominated by Fagaceae existed in northern Thailand during the late Oligocene–Early Miocene, which differs from the present-day tropical monsoon forest there, reflecting a significant change from warm-humid to modern seasonally hot-dry climate. We propose that the dramatic climate change and restructuring of vegetation composition were driven by several factors, including the Oligocene global cooling event and the tectonic southward extrusion of the Southeast Asian landmass, which imposed a long-term latitudinal shift.

Sequoia was widely distributed across the Northern Hemisphere during the Cenozoic, yet our understanding of its biogeographic history remains limited due to relatively scarce fossil records in certain regions, particularly East Asia. A new Sequoia leaf fossil record from the Late Eocene to Early Oligocene in Yunnan Province of southwestern China displays morphological similarity to the fossil species S. maguanensis, such as an alternate leaf arrangement with a decurrent base, straight epidermal cell walls, and stomata surrounded by four subsidiary cells. Using the MaxEnt model and S. sempervirens (the only extant species of Sequoia) as a reference, we identified optimal potential distribution areas for Sequoia from the Palaeocene to the Pliocene. Our results indicate that Sequoia, which thrived in warm and humid conditions, progressively shifted its range southward as global temperatures declined from the Eocene to the Pliocene, contracting its habitat towards lower latitudes. Our analysis suggests that Sequoia likely originated in East Asia during the Early Cretaceous and subsequently spread to North America via the Bering Land Bridge. During the Palaeocene, it extended its range to Greenland and Svalbard, eventually reaching western Europe during the Eocene. In the Oligocene, Sequoia was widespread across Europe and reached Siberia, later expanding from East Asia to the Mediterranean and northern Thailand by the Miocene. Quaternary glaciations led to its near-complete disappearance in Eurasia and North America, with only remnant populations surviving along the western coast of the United States. This study also highlights the role of morphological stasis in Sequoia alongside the intensification of the monsoon climate as key factors contributing to its eventual disappearance in southwestern China.

The Eocene-Oligocene transition (EOT) represents a critical period in Earth's climate system, marked by a shift from a "warmhouse" to a "coolhouse" climate. This critical interval, spanning approximately 34 million years ago, was primarily characterised by a rapid decline in atmospheric CO2 concentrations. This decline ultimately triggered pronounced global cooling, aridification and the initial development and growth of the Antarctic ice sheet, all of which profoundly influenced the evolution, distribution, and diversity of vegetation. While there is a consensus regarding the decline in sea surface temperatures during the EOT, the terrestrial temperature response to the EOT remains a subject of ongoing debate, particularly concerning spatial heterogeneity and latitudinal gradients. The primary drivers of the EOT are also under active investigation. Although various hypotheses-including orbital forcing, a drop in CO2 concentrations, and thermal isolation-have been supported by numerical simulations, a single dominant forcing factor has yet to be identified. The global vegetation response to the EOT is evident in the retreat of forests, a decrease in thermophilic flora, and the expansion of drought-tolerant species. However, significant regional variations exist in species diversity. Currently, systematic research is still relatively sparse regarding how EOT global climate change comprehensively drove the co-evolution of terrestrial ecosystems across broader spatial and continuous temporal scales. Currently, spatiotemporal uncertainty in palaeovegetation data makes it difficult to link the co-evolution of ecosystems with climate change across the EOT. To better resolve this, we integrate palaeo-vegetation proxies with palaeoclimate simulations from HadCM3 with interactive vegetation, as well as an offline vegetation model (SDGVM). Our analysis indicates that consistent global terrestrial cooling across all latitudes (high, mid, and low) during the EOT drove changes in ecosystem development, with high latitudes experiencing more pronounced seasonal temperature variations. The vegetation simulations reveal trends of forest opening and the expansion of C-4 grasses, although these findings occasionally show local inconsistencies with fossil records. To bridge these gaps, future research should integrate big data with numerical simulations, establish high-precision spatiotemporal frameworks, and develop more reliable climate and vegetation models. This approach will enhance our understanding of the co-evolutionary mechanisms between climate and vegetation during the EOT. This review offers a deep-time perspective for predicting how terrestrial ecosystems may respond to future climate change. By integrating multi-source data and models, we can unravel the complexities of climate-biosphere interactions, thereby providing crucial theoretical support for global change research.

As anthropogenic carbon emissions continue to rise, global temperatures are experiencing unprecedented increases. In response to the looming threats of climate change, the Paris Agreement proposed the goal of limiting global warming to 1.5-2.0 degrees C and advocated for global emission reductions. However, recent studies suggest that even if these targets are met, internal feedback mechanisms within the climate system could still propel global warming beyond critical thresholds, potentially shifting Earth's climate from cyclical glacial-interglacial alternation to a hothouse state. Notably, 2024 was the hottest year on record, with the global average surface temperature 1.55 degrees C higher than pre-industrial levels, making it the first calendar year since the Industrial Revolution to exceed 1.5 degrees C of warming. If the current warming trend observed in recent decades continues, the Earth's average temperature could reach 20 degrees C by similar to 2300, resulting in a permanent hothouse state. This alarming prospect raises concerns within both the scientific community and the general public about the potential for catastrophic outcomes. The Cretaceous-Paleogene period represents Earth's most recent prolonged hothouse state, characterized by sustained high temperatures and elevated atmospheric CO2 concentrations. Understanding this period offers critical insights into future climate scenarios. This study synthesizes current knowledge of the Cretaceous-Paleogene hothouse Earth, exploring its driving mechanisms, environmental characteristics, ecological responses, and ultimate termination. Key findings include: (1) through integrated analysis of carbon emission patterns from mid-ocean ridges, continental rifts, large igneous provinces, and continental arcs, coupled with paleoclimatic records, we propose that continental arc magmatism was likely the primary driver of the Cretaceous-Paleogene hothouse conditions. (2) Multiple episodes of carbon cycle perturbations, lasting 10(4)-10(5) years, characterized the hothouse climate regime, driving rapid climatic warming events. These include the Cretaceous Oceanic Anoxic Events (OAEs) and the Paleogene hyperthermal events (e.g., the Paleocene-Eocene Thermal Maximum (PETM)). The OAEs are characterized by extensive black shale deposition, with distinct positive carbon isotope excursions observed during OAE1a, OAE1d, and OAE2, while OAE1b is marked by a notable negative excursion. In contrast, the Paleogene hyperthermal events consistently exhibit negative carbon isotope excursions with limited black shale deposition. This pronounced dichotomy in geochemical signatures and depositional patterns between these events can be primarily explained by fundamental differences in both the nature of carbon sources and the underlying perturbation mechanisms. (3) Hyperthermal events, characterized by pronounced negative carbon isotope excursions, occurred during prolonged periods of warming, indicating increased vulnerability of Earth's surface organic carbon reservoirs to increases in global temperature. OAE1b, PETM, and subsequent Eocene hyperthermal events were likely triggered by perturbations in these reservoirs, highlighting the necessity for comparative studies on their respective carbon emission fluxes and associated environmental impacts. (4) The hyperthermal events were associated with intensified hydrological cycles, characterized by enhanced high-latitude precipitation and complex spatial variability in mid-to low-latitude rainfall patterns. (5) The hothouse climate facilitated the expansion and diversification of thermophilic plant groups, promoting the spread of forest from low to middle and high latitudes and enhancing terrestrial plant diversity. In marine environments, there was also an increase in the diversity of dinoflagellate cysts, calcareous nannofossils, and planktic foraminifera. This synthesis highlights that the Cretaceous-Paleogene hothouse state was fundamentally maintained by deep Earth carbon emissions, while its termination was governed by carbon sequestration through enhanced chemical weathering and organic matter burial. However, significant uncertainties remain regarding quantitative carbon fluxes, spatial patterns of hydrological changes, and ecosystem responses to rapid warming. Future research directions should emphasize integrated Earth system approaches to better constrain these critical aspects of hothouse Earth dynamics.

Relict plants are those that once had a wide distribution but are now restricted to small areas. It is important to study the process of their distribution in the geological past to better understand the climatic factors that shape their current distribution. Metasequoia is one of the best-known genera of relict plants in Asia, with rich fossil records dating back to the Late Cretaceous. In this study, we used Deep-time Ecological Niche Modelling (DENM) and 755 Cenozoic megafossil records of Metasequoia to understand the pattern of its historical distribution and driving factors. The results showed that Metasequoia was widely distributed across mid-high-latitude regions during the Paleogene. Its distribution range contracted toward lower latitudes during the Neogene due to global aridification and cooling. Our results indicate that mean annual precipitation was the key factor shaping the distribution of Metasequoia during the Paleogene and Neogene. Later during the Pleistocene, a dramatic contraction of its distribution occurred due to glaciations, which also shaped the modern distributions of many relict plants in China. Our study supports that climate change is the main factor driving the distribution of relict plants and therefore provides crucial evidence for understanding their biogeographic histories and future conservation under climate change.

The Cenozoic development of the monsoon system in Asia drove major biome shifts, however early plant responses to its seasonality remain obscure. Ring-porosity, a functional trait of woody angiosperms associated with deciduousness and seasonal water demand, provides a profound insight into how xylem formation was influenced by monsoon-driven precipitation seasonality. Here, we report the oldest known Cenozoic ring-porous wood in tropical Asia, Parasalicaceoxylon naduongensis Nguyen et Oskolski gen. et sp. nov. (Salicaceae) from the upper Eocene of the Na Duong Basin, northern Vietnam. The fossil wood exhibits distinctive ring porosity, indicating deciduous phenology and seasonal growth in a tropical environment. HadCM3BL paleoclimate simulations reveal strong precipitation seasonality driven by latitudinal migration of the Intertropical Convergence Zone (ITCZ), consistent with an ITCZ monsoon affecting northern Vietnam during the late Eocene. Combined with extant and fossil ring-porous wood records from Asia, this suggests that evolution of deciduousness and ring porosity in East Asia was driven by monsoon seasonality.