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Our growing understanding of the plant tree of life provides a novel opportunity to uncover the major drivers of angiosperm diversity. Using a time-calibrated phylogeny, we characterized hot and cold spots of lineage diversification across the angiosperm tree of life by modeling evolutionary diversification using stepwise AIC (MEDUSA). We also tested the whole-genome duplication (WGD) radiation lag-time model, which postulates that increases in diversification tend to lag behind established WGD events. Diversification rates have been incredibly heterogeneous throughout the evolutionary history of angiosperms and reveal a pattern of ‘nested radiations’ – increases in net diversification nested within other radiations. This pattern in turn generates a negative relationship between clade age and diversity across both families and orders. We suggest that stochastically changing diversification rates across the phylogeny explain these patterns. Finally, we demonstrate significant statistical support for the WGD radiation lag-time model. Across angiosperms, nested shifts in diversification led to an overall increasing rate of net diversification and declining relative extinction rates through time. These diversification shifts are only rarely perfectly associated with WGD events, but commonly follow them after a lag period.

Aims The tropical niche conservatism (TNC) hypothesis and the out of the tropics (OTT) hypothesis propose mechanisms generating patterns of species diversity across warm‐to‐cold thermal gradients at large spatial scales. These two hypotheses both integrate ecological and biogeography‐related evolutionary factors, but they predict opposite patterns for phylogenetic structure. Mount Namjagbarwa possesses one of the longest elevational gradients for flowering plant diversity in the world. We aim to analyse the elevational patterns of the phylogenetic structure of flowering plants in this mountain, and investigate underlying causes for the emergence of the patterns. Location Mt. Namjagbarwa located at the eastern edge of the Himalaya. Methods Species distribution data of Mt. Namjagbarwa were extracted from specimen records in online sources, literature, herbarium and our fieldwork. Bioclimatic data were extracted from the CHELSA database. Mt. Namjagbarwa was divided into 100‐m elevational belts, which were grouped into three elevation segments (100–2000 m, 2000–4000 m and 4000–5200 m) for data analysis. We calculated phylogenetic metrics for each belt. The relationships of phylogenetic metrics with elevation and climatic factors were analysed using generalized additive models and structural equation models. Results A typical hump‐shaped pattern of species richness was observed along the elevational gradient of Mt. Namjagbarwa. However, the phylogenetic structure showed a zig‐zag pattern with the three elevation segments, each of which has different formation mechanisms. Temperature tolerance played important roles throughout the entire elevational gradient in species richness and phylogenetic structure. Main conclusions Neither TNC nor OTT alone can fully explain the patterns of floristic assembly of the entire elevational gradient of Mt. Namjagbarwa. OTT and TNC are better explanation for the patterns of low and middle elevations respectively. Potential mechanisms for species assembly of different elevation segments in Mt. Namjagbarwa region alternate between niche convergence and niche conservatism. The patterns observed in this study are likely to be common across the entire Himalaya. This is important for preserving the evolutionary potential of mountain biodiversity. However, more studies are needed to determine the underlying mechanisms generating the zig‐zag pattern of the phylogenetic structure in the Himalaya.

Species richness varies dramatically among groups of organisms, yet the causes of this variation remain poorly understood. Variation in species‐level diversification rates may partially explain differential species richness among clades, but older clades should also be more diverse, because they will have had more time to accumulate species. Surprisingly, studies that have investigated this question have reached dramatically different conclusions: several claim to find no such age‐diversity relationship, whereas a recent and more inclusive study reported that clade age and not diversification rate explains the variation in species richness among animal taxa. Here I address the relationship between clade age and species richness using a model‐based approach that controls for variation in diversification rates among clades. I find that species richness is effectively independent of clade age in four of five data sets. Even extreme among‐clade variation in diversification rates cannot account for the absence of a positive age‐diversity relationship in angiosperms, birds, and teleost fishes. I consider two alternative explanations for these results and find that a clade volatility model positing correlated speciation‐extinction dynamics does not underlie these patterns. Rather, ecological limits on clade growth, such as geographic area, appear to mediate temporal declines in diversification within higher taxa.

More than a decade of phylogenetic research has yielded a well-sampled, strongly supported hypothesis of relationships within the large (> 4000 species) plant family Acanthaceae. This hypothesis points to intriguing biogeographic patterns and asymmetries in sister clade diversity but, absent a time-calibrated estimate for this evolutionary history, these patterns have remained unexplored. Here, we reconstruct divergence times within Acanthaceae using fossils as calibration points and experimenting with both fossil selection and effects of invoking a maximum age prior related to the origin of Eudicots. Contrary to earlier reports of a paucity of fossils of Lamiales (an order of ~23,000 species that includes Acanthaceae) and to the expectation that a largely herbaceous to soft-wooded and tropical lineage would have few fossils, we recovered 51 reports of fossil Acanthaceae. Rigorous evaluation of these for accurate identification, quality of age assessment and utility in dating yielded eight fossils judged to merit inclusion in analyses. With nearly 10 kb of DNA sequence data, we used two sets of fossils as constraints to reconstruct divergence times. We demonstrate differences in age estimates depending on fossil selection and that enforcement of maximum age priors substantially alters estimated clade ages, especially in analyses that utilize a smaller rather than larger set of fossils. Our results suggest that long-distance dispersal events explain present-day distributions better than do Gondwanan or northern land bridge hypotheses. This biogeographical conclusion is for the most part robust to alternative calibration schemes. Our data support a minimum of 13 Old World (OW) to New World (NW) dispersal events but, intriguingly, only one in the reverse direction. Eleven of these 13 were among Acanthaceae s.s., which comprises > 90% of species diversity in the family. Remarkably, if minimum age estimates approximate true history, these 11 events occurred within the last ~20 myr even though Acanthaceae s.s is over 3 times as old. A simulation study confirmed that these dispersal events were significantly skewed toward the present and not simply a chance occurrence. Finally, we review reports of fossils that have been assigned to Acanthaceae that are substantially older than the lower Cretaceous estimate for Angiosperms as a whole (i.e., the general consensus that has resulted from several recent dating and fossil-based studies in plants). This is the first study to reconstruct divergence times among clades of Acanthaceae and sets the stage for comparative evolutionary research in this and related families that have until now been thought to have extremely poor fossil resources.

We aim to test hypotheses on the patterns of clade age of climbing plants under climatic variations along the latitudinal gradients in China. Specifically, we uncover their general patterns of mean family age (MFA) and their climatic drivers. We evaluate the extents to which both the tropical niche conservatism hypothesis (TNC) and the out of the tropics hypothesis (OTT) can account for the MFA of climbing plants, respectively. A dataset including 2487 climbing species was used to quantify geographical patterns of MFA across China. Spatial regression analyses with information‐theoretical multi‐model selections were performed to estimate the importance of climatic variables. There were generally increasing trends of MFA from low to high latitudes for all types of climbers. For woody climbers, MFA was negatively correlated with minimum temperature and annual mean precipitation but positively correlated with seasonal temperature and precipitation, and was mostly influenced by mean temperature of the coldest quarter. For herbaceous vines, the MFA pattern showed relatively insignificant correlations with all the climatic variables. Our results highlight that the OTT hypothesis offers a promising explanation for the latitudinal MFA gradients of climbers in China (especially for woody climbers), which turn out to be contrary to the TNC predictions. The first survey concerning the geographical patterns of climbers in regional scale (in China). The mean family ages (MFA) of climbers and trees showed opposite trends with increasing latitude. The increasing MFA of woody climbers with increasing latitude could be effectively explained by the ‘out of the tropics hypothesis’.

It has long been known that species should not be distributed randomly in morphospace (a multidimensional trait space), even under simple models of evolution. However, recent studies suggest that position in morphospace can affect aspects of evolution such as the durations of clades and the species richness of their constituent taxa. Here we investigate the dynamics of morphospace occupancy in living and fossil marine bivalves using shell size and aspect ratio, two functionally important traits. Multiple lines of evidence indicate that the center of a family's morphospace today represents a location where taxonomic diversity is maximized, apparently owing to lower extinction rates. Within individual bivalve families, species with narrow geographic ranges are distributed throughout the morphospace but widespread species, which are generally expected to be extinction resistant, tend to be concentrated near the center. The morphospace centers of most species-rich families today (defined as the median value for all species in the family) tend to be close to the positions of the family founders, further suggesting an association between position in morphospace and net diversification rates. However, trajectories of individual subclades (genera) are inconsistent with the center of morphospace being an evolutionary attractor.

1. The ecological conditions promoting evolutionary priority effects, where the order and timing of ancestral species arrival into a new habitat influences extant community assembly, are poorly understood. Studies in the New Zealand alpine indicated that early-arriving angiosperm lineages dominated communities via niche pre-emption. Forests have a much longer (>60 myr) evolutionary history in New Zealand than alpine communities (<2 myr) and greater structural complexity. 2. Here we ask whether community effects of arrival order persist in cool temperate forest communities in southern New Zealand that have assembled throughout the Cenozoic. Combining phylogenetically derived clade ages and forest vegetation data from across a mountain range, we compare effects of clade age on relative richness and abundance of two taxonomic groups (pteridophytes and angiosperms) along precipitation gradients. 3. We show that older clades of both groups tended to have greater relative abundance and older angiosperm clades had greater relative richness. Relative richness and abundance also increased with regional clade diversity, independent of clade age. 4. The strength of the clade age effect on community dominance changed differently along precipitation gradients depending on the response and taxonomic group. Clade age had a stronger effect on relative abundance of pteridophytes with increasing elevation and westerliness (i.e. as precipitation increased). In contrast, the effect of clade age on relative abundance of angiosperms decreased with westerliness. Precipitation did not alter the clade age effect on relative richness. 5. Synthesis. We show that evolutionary priority effects persist in communities with a longer evolutionary history than has been investigated to date and across physiologically contrasting taxonomic groups, suggesting priority effects are general drivers of community assembly over macro-evolutionary time-scales. Furthermore, the strength of evolutionary priority effects attenuated along a gradient of decreasing resources, at least for pteridophytes, which improves our ability to predict conditions in which the arrival order of lineages influences community assembly.

Penalized likelihood estimated ages of both densely sampled intracontinental and sparsely sampled transcontinental crown clades in the legume family show a mostly Quaternary to Neogene age distribution. The mode ages of the intracontinental crown clades range from 4-6 Myr ago, whereas those of the transcontinental crown clades range from 8-16 Myr ago. Both of these young age estimates are detected despite methodological approaches that bias results toward older ages. Hypotheses that resort to vicariance or continental history to explain continental disjunct distributions are dismissed because they require mostly Palaeogene and older tectonic events. An alternative explanation centring on dispersal that may well explain the geographical as well as the ecological phylogenetic structure of legume phylogenies is Hubbell's unified neutral theory of biodiversity and biogeography. This is the only dispersalist theory that encompasses evolutionary time and makes predictions about phylogenetic structure.

Three types of anatomically preserved vegetative shoots with features that characterize crown group Equisetum have been discovered in Lower Cretaceous deposits ([almost equal to]136 Ma) of British Columbia, Canada, suggesting the genus is much older than currently believed. Specimens include two types of aerial shoots described as E. haukeanum sp. nov. and E. vancouverense sp. nov. and one type of subterranean rhizome. Shoots are 1-2 mm in diameter, jointed, and in cross section have fluted stems with a hollow pith. Distinctive patterns of cortical sclerenchyma and different ridge morphologies characterize each shoot morphotype. Nodes display irregular branching, highly fused leaf sheaths, and a nodal diaphragm. The aerial stem morphospecies have vallecular canals on alternating radii with carinal canals of an equisetostele surrounded by only a few tracheids. No secondary tissues are produced. Bands of surficial stomata flank the furrows of one morphospecies. Rhizomes and aerial shoots are of a similar size, suggesting that the plants were equivalent in stature to the smallest living Equisetum species. These fossils augment our understanding of evolutionary transformations that led from Paleozoic Archaeocalamitaceae and Calamitaceae to crown group Equisetaceae, suggesting that the initial diversification of Equisetum began far earlier than suggested by molecular-clock-based estimates.