Increases in drought-induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P50 ) of 13 woody species endemic to New Caledonia and with different xylem conduit morphologies. We examined the relation between P50 , along with other leaf and xylem functional traits, and a range of habitat variables. Selected species had P50 values ranging between -4.03 and -2.00 MPa with most species falling in a narrow range of resistance to embolism above -2.7 MPa. Embolism vulnerability was significantly correlated with elevation, mean annual temperature and percentage of species occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P50 . Commonly used functional traits such as wood density and leaf traits were not related to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as a major driver of species environmental distribution. Drought-induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rain forest woody species.

Gaps between molecular ages and fossils undermine the validity of time-calibrated molecular phylogenies. An example of the time gap surrounds the age of angiosperm's origin. We calculate molecular ages of the earliest flowering plant lineages using 22 fossil calibrations (101 genera, 40 families). Our results reveal the origin of angiosperms at the late Permian, ~275 million years ago. Different prior probability curves of molecular age calculations on dense calibration point distributions had little effect on overall age estimates compared to the effects of altered calibration points. The same is true for reasonable root age constraints. We conclude that our age estimates based on multiple datasets, priors, and calibration points are robust and the true ages are likely between our extremes. Our results, when integrated with the ecophysiological evolution of early angiosperms, imply that the ecology of the earliest angiosperms is critical to understand the pre-Cretaceous evolution of flowering plants.

Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals incorporated into plant organic matter and atmospheric gases. Models describing evaporative enrichment of leaf water have become increasingly complex over time, reflecting enhanced spatial and temporal resolution. We recommend that practitioners choose a model with a level of complexity suited to their application, and provide guidance. At the same time, there exists some lingering uncertainty about the biophysical processes relevant to patterns of isotopic enrichment in leaf water. An important goal for future research is to link observed variations in isotopic composition to specific anatomical and physiological features of leaves that reflect differences in hydraulic design. New measurement techniques are developing rapidly, enabling determinations of both transpired and leaf water δ 18 O and δ 2 H to be made more easily and at higher temporal resolution than previously possible. We expect these technological advances to spur new developments in our understanding of patterns of stable isotope fractionation in leaf water.

Canellales, a clade consisting of Winteraceae and Canellaceae, represent the smallest order of magnoliid angiosperms. The clade shows a broad distribution throughout the Southern Hemisphere, across a diverse range of dry to wet tropical forests. In contrast to their sister-group, Winteraceae, the phylogenetic relations and biogeography within Canellaceae remain poorly studied. Here we present the phylogenetic relationships of all currently recognized genera of Canellales with a special focus on the Old World Canellaceae using a combined dataset consisting of the chloroplast trnK-matK-trnK-psbA and the nuclear single copy gene mag1 (Maigo 1). Within Canellaceae we found high statistical support for the monophyly of Warburgia and Cinnamosma. However, we also found relationships that differ from previous studies. Cinnamodendron splitted into two clades, a South American clade and a second clade confined to the Antilles and adjacent areas. Cinnamodendron from the Antilles, as well as Capsicodendron, South American Cinnamodendron and Pleodendron were not monophyletic. Consequently, Capsicodendron should be included in the South American Cinnamodendron clade and the genus Pleodendron merged with the Cinnamodendron clade from the Antilles. We also found that Warburgia (restricted to mainland eastern Africa) together with the South American Cinnamodendron and Capsicodendron are sister to the Malagasy genus Cinnamosma. In addition to the unexpected geographical relationships, both biogeographic and molecular clock analyses suggest vicariance, extinction, and at least one intercontinental long-distance-dispersal event. Our dating result contrasts previous work on Winteraceae. Diversification of Winteraceae took place in the Paleocene, predating the Canellaceae diversification by 13 MA in the Eocene. The phylogenetic relationships for Canellaceae supported here offer a solid framework for a future taxonomic revision of the Canellaceae.

Premise of the study: Phylogenetic incongruence between "gene trees" and "species trees" has been widely acknowledged in phylogenetic research. Conflicts may emerge from several processes including paralogy, hybridization, and incomplete lineage sorting. Although phylogenetic incongruence appears common, its impact on many phylogeny-based analyses remains poorly understood.Methods: We examined the occurrence of phylogenetic conflict between nuclear (ribosome ITS) and plastid (rbcL, trnL-F, rpl20-rps12, and rps16 intron) loci in the ancient angiosperm family Chloranthaceae. Then we investigated how phylogenetic conflict bears on taxonomic classification within the family as well as on inferences on biogeographical history, floral evolution, and measures of phylogenetic diversity (PD).Key results: We found evidence for significant phylogenetic incongruence between plastid and nuclear data in the genus Hedyosmum. Within Hedyosmum, our results did not support previous subgeneric classification of the genus. Division of sections within subgenus Tafalla was supported by the ITS data but not by the plastid data set. As a consequence, we showed that inferring the evolution of key floral characters and geographical history within Hedyosmum depends on the phylogenetic data used. Both data sets yielded similar PD measures across genera, but we found contrasting PD measures in Hedyosmum, even after correcting for rate heterogeneity.Conclusions: Our study demonstrated that phylogenetic conflict not only affects the inference of organismal relationships but also impacts our understanding of biogeographical history, morphological evolution, and phylogenetic diversity.

Summary The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves. A well‐known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water). We tested this safety–efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species. Safety was considered at three levels: the xylem water potentials where 12%, 50% and 88% of maximal conductivity are lost. Although correlations between safety and efficiency were weak ( r 2 < 0.086), no species had high efficiency and high safety, supporting the idea for a safety–efficiency tradeoff. However, many species had low efficiency and low safety. Species with low efficiency and low safety were weakly associated ( r 2 < 0.02 in most cases) with higher wood density, lower leaf‐ to sapwood‐area and shorter stature. There appears to be no persuasive explanation for the considerable number of species with both low efficiency and low safety. These species represent a real challenge for understanding the evolution of xylem.

Aim In New Caledonia, relictual angiosperm lineages are over-represented. However, the mechanisms responsible for such a distribution remain unclear. Two key hypotheses are that: (1) the diversity reflects adaptation to ultramafic substrates that ecologically filtered plant colonists; and (2) the diversity stems from wet climatic conditions that have persisted in New Caledonia during the late Quaternary while Australia and some nearby islands experienced widespread extinction events. Here, we investigate which hypothesis better explains the disharmony of relict angiosperms in New Caledonia.Location New Caledonia (South West Pacific Ocean).Methods We built species distribution models from herbarium data to determine the environmental correlates for 60 relict angiosperm taxa. Environmental variables used to characterize habitats included vegetation, substrate, and climate variables. We then tested whether the variety of xylem conduit structures borne by New Caledonian relict angiosperms, which is expected to affect plant hydraulic capacity, was correlated with habitat preference. Finally, we analysed species prevalence on different substrates and projected habitat size and distribution to the Last Glacial Maximum (LGM).Results We found a clear habitat preference among relict angiosperms for rain forests located on non-ultramafic substrates, with the exception of taxa bearing true vessels with simple perforation plates, which harboured a wider habitat breadth. We also showed that these rain forest habitats experienced a range reduction and an eastward shift during the LGM, forming two refugial areas located on the warm and rainy east coast of Grande Terre.Main conclusions Prevalence of relict angiosperms in habitats characterized by low evaporative demand appears to be related to xylem hydraulic limitations. The disharmony of relict angiosperms in New Caledonia therefore arose from the persistence of rain forests in the island despite global fluctuations in climate during the Quaternary that affected floras in the region. Our study offers a new model to explain why certain angiosperm families are disharmonically represented in New Caledonia.

Chapter 17 The evolution of angiosperm lianescence: a perspective from xylem structure-function Sandrine Isnard, Sandrine Isnard IRD, UMR AMAP, Laboratoire de Botanique et d'Écologie Végétale Appliquées, Nouméa, Nouvelle-CalédonieSearch for more papers by this authorTaylor S. Feild, Taylor S. Feild James Cook University, Townsville, Queensland, AustraliaSearch for more papers by this author Sandrine Isnard, Sandrine Isnard IRD, UMR AMAP, Laboratoire de Botanique et d'Écologie Végétale Appliquées, Nouméa, Nouvelle-CalédonieSearch for more papers by this authorTaylor S. Feild, Taylor S. Feild James Cook University, Townsville, Queensland, AustraliaSearch for more papers by this author Book Editor(s):Stefan A. Schnitzer, Stefan A. Schnitzer University of Wisconsin–Milwaukee, WI, USASearch for more papers by this authorFrans Bongers, Frans Bongers Wageningen University and Research Centre, The NetherlandsSearch for more papers by this authorRobyn J. Burnham, Robyn J. Burnham University of Michigan, MI, USASearch for more papers by this authorFrancis E. Putz, Francis E. Putz University of Florida, FL, USASearch for more papers by this author First published: 18 October 2014 https://doi.org/10.1002/9781118392409.ch17Citations: 12 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onEmailFacebookTwitterLinkedInRedditWechat Summary The evolution of lianas has punctuated the history of land plants, with the angiosperm lineages representing the most recent stage of liana exploration. The model of lianas as fast-growing, disturbance-loving plants emerges largely from the function of eudicot and magnoliid angiosperms. This chapter looks at some specific properties of ecology and function, derived from functional aspects of stem hydraulics, which appear to be restricted to lianas. 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UNLABELLED:•PREMISE OF STUDY:Have Gondwanan rainforest floral associations survived? Where do they occur today? Have they survived continuously in particular locations? How significant is their living floristic signal? We revisit these classic questions in light of significant recent increases in relevant paleobotanical data.•METHODS:We traced the extinction and persistence of lineages and associations through the past across four now separated regions-Australia, New Zealand, Patagonia, and Antarctica-using fossil occurrence data from 63 well-dated Gondwanan rainforest sites and 396 constituent taxa. Fossil sites were allocated to four age groups: Cretaceous, Paleocene-Eocene, Neogene plus Oligocene, and Pleistocene. We compared the modern and ancient distributions of lineages represented in the fossil record to see if dissimilarity increased with time. We quantified similarity-dissimilarity of composition and taxonomic structure among fossil assemblages, and between fossil and modern assemblages.•KEY RESULTS:Strong similarities between ancient Patagonia and Australia confirmed shared Gondwanan rainforest history, but more of the lineages persisted in Australia. Samples of ancient Australia grouped with the extant floras of Australia, New Guinea, New Caledonia, Fiji, and Mt. Kinabalu. Decreasing similarity through time among the regional floras of Antarctica, Patagonia, New Zealand, and southern Australia reflects multiple extinction events.•CONCLUSIONS:Gondwanan rainforest lineages contribute significantly to modern rainforest community assembly and often co-occur in widely separated assemblages far from their early fossil records. Understanding how and where lineages from ancient Gondwanan assemblages co-occur today has implications for the conservation of global rainforest vegetation, including in the Old World tropics.

High vein density (D(V)) evolution in angiosperms represented a key functional transition. Yet, a mechanistic account on how this hydraulic transformation evolved remains lacking. We demonstrate that a consequence of producing high D(V is that veins must become very small to fit inside the leaf, and that angiosperms are the only clade that evolved the specific type of vessel required to yield sufficiently conductive miniature leaf veins. From 111 species spanning key divergences in vascular plant evolution, we show, using analyses of vein conduit evolution in relation to vein packing, that a key xylem innovation associated with high D(V) evolution is a strong reduction in vein thickness and simplification of the perforation plates of primary xylem vessels. Simple perforation plates in the leaf xylem occurred only in derived angiosperm clades exhibiting high D(V) (> 12 mm mm(-2)). Perforation plates in the vessels of other species, including extant basal angiosperms, consisted of resistive scalariform types that were associated with thicker veins and much lower D(V). We conclude that a reduction in within-vein conduit resistance allowed vein size to decrease. We suggest that this adaptation may have been a critical evolutionary step that enabled dramatic D(V) elaboration in angiosperms.

Iterophyllum lobatum gen. et sp. nov. is reported from the late Barremian lithographic limestones of Las Hoyas, Spain. It consists of a simple, petiolate leaf, with a pinnately lobed lamina. The dentate thickened margin bears chloranthoid-like glands at lobe apices and sinuses. The venation is pinnate and craspedodromous, with three discernible vein orders. Based on the low regularity of vein course and angles and the low leaf rank, such a venation pattern may represent an early evolved leaf archetype in early basal eudicots. An acropetal leaf development mode in I. lobatum is similar to that in several living Papaveraceae. The leaf architecture and ecophysiology, particularly the vein widths and the glands, indicate that I. lobatum leaves were aerial. The plant grew close to water in the wetland terrestrial ecosystem of Las Hoyas. Iterophyllum lobatum might have been an opportunist species in early ecological succession stages after wildfires.(c) 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 594-605.

Early angiosperm evolution, beginning approximately 140 million years ago, saw many innovations that enabled flowering plants to alter ecosystems globally. These included the development of novel, flower-based pollinator attraction mechanisms and the development of increased water transport capacity in stems and leaves. Vein length per area (VLA) of leaves increased nearly threefold in the first 30-40 million years of angiosperm evolution, increasing the capacity for transpiration and photosynthesis. In contrast to leaves, high water transport capacities in flowers may not be an advantage because flowers do not typically contribute to plant carbon gain. Although flowers of extant basal angiosperms are hydrated by the xylem, flowers of more recently derived lineages may be hydrated predominantly by the phloem. In the present study, we measured leaf and flower VLA for a phylogenetically diverse sample of 132 species from 52 angiosperm families to ask (i) whether flowers have lower VLA than leaves, (ii) whether flowers of basal angiosperm lineages have higher VLA than more recently derived lineages because of differences between xylem and phloem hydration, and (iii) whether flower and leaf VLA evolved independently. It was found that floral structures had lower VLA than leaves, but basal angiosperm flowers did not have higher VLA than more derived lineages. Furthermore, the independent evolution of leaf and petal VLA suggested that these organs may be developmentally modular. Unlike leaves, which have experienced strong selection for increased water transport capacity, flowers may have been shielded from such selective pressures by different developmental processes controlling VLA throughout the plant bauplan.

Evolutionary radiations in growth forms represented key events in the rise of early angiosperm success. However, understanding the directions of early angiosperm growth lability and the traits determining growth form innovations remain unclear. Lianescence appears to represent an early evolved direction of early angiosperm growth form experimentation, owing to occurrence of lianas in the extant, early diverging clade Austrobaileyales. Here we examine biomechanical and hydraulic ecophysiology of Schisandra glabra (Schisandraceae) in the context of its habitat and xylem form-function to test hypotheses about the functional performance of basal angiosperm lianescence. We found that S. glabra evolved much higher twist-bend flexibility, greater hydraulic efficiency, and capacity as compared to a nonclimbing relative from similar habitats, Illicium floridanum. However, lianescence was not associated with increased leaf photosynthetic capacity, drought tolerance, or a more cheaply constructed body plan. We found that a small number of stem structural shifts, involving primarily increases in cell sizes of vessels, tracheids, and the proportions of living tissues, were involved in exploration of the liana habit in the Austrobaileyales. Our results suggest that evolution of early angiosperm lianescence was potentially a relatively facile transition involving relatively small changes in xylem structure to achieve large change in stem biomechanical performance.

Previous articleNext article No AccessCelebrating Giant Steps toward a Synthetic History of Angiosperm EvolutionTaylor S. Feild and Erika J. EdwardsTaylor S. Feild*School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia Search for more articles by this author and Erika J. Edwards†Department of Ecology and Evolutionary Biology, Brown University, 80 Waterman Street, Box G-W, Providence, Rhode Island 02912, U.S.A. Search for more articles by this author PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by International Journal of Plant Sciences Volume 173, Number 6July/August 2012 Article DOIhttps://doi.org/10.1086/666546 Views: 101Total views on this site HistoryReceived May 2012Revised May 2012 © 2012 by The University of Chicago. All rights reserved.PDF download Crossref reports no articles citing this article.

A hypothesized advantage of the building block of the angiosperm vascular network, the vessel, is often cited as a critical innovation that elevated the competitive abilities of early angiosperms above nonangiosperms during the Cretaceous. Here we synthesize recent discoveries on the hydraulic functions of living basal angiosperm lineages with evidence from the fossil record to trace the early evolutionary significance of vessels in the early ecophysiological radiation of angiosperms. Evidence from extant comparative biology and the Early Cretaceous fossil record of leaves and wood do not support the hypotheses that vessels improved drought tolerance of angiosperms, increased angiosperm's photosynthetic abilities, or provided an immediate leap in hydraulic capacity. Instead, later tuning of vessel structure for increased flow efficiency-in particular, by the evolution of simple perforation plates-enabled major increases in xylem hydraulic efficiency.

Analysis of data from forest plants worldwide shows that margins between threshold xylem pressures at which plants suffer damage and the lowest xylem pressures experienced are small, with no difference between dry and wet forests, providing insight into why drought-induced forest decline is occurring in both arid and wet forests. Forest dieback resulting from extreme drought events has the potential to cause widespread loss of biodiversity, with a major impact on the global carbon balance. Plants undergoing drought stress experience reduced xylem pressure, and each species can tolerate a different degree of reduction before xylem damage and, eventually, hydraulic failure occur. This study looks at the safety margin between minimum experienced xylem pressure and the damage threshold for 226 forest species from 81 sites worldwide and shows that most species across both dry and wet biomes have small safety margins against injurious levels of drought stress. These plants are potentially vulnerable to the combination of rising temperatures and declining rainfall that is predicted to cause droughts of increasing intensity and duration in the near future. Shifts in rainfall patterns and increasing temperatures associated with climate change are likely to cause widespread forest decline in regions where droughts are predicted to increase in duration and severity1. One primary cause of productivity loss and plant mortality during drought is hydraulic failure2,3,4. Drought stress creates trapped gas emboli in the water transport system, which reduces the ability of plants to supply water to leaves for photosynthetic gas exchange and can ultimately result in desiccation and mortality. At present we lack a clear picture of how thresholds to hydraulic failure vary across a broad range of species and environments, despite many individual experiments. Here we draw together published and unpublished data on the vulnerability of the transport system to drought-induced embolism for a large number of woody species, with a view to examining the likely consequences of climate change for forest biomes. We show that 70% of 226 forest species from 81 sites worldwide operate with narrow (<1 megapascal) hydraulic safety margins against injurious levels of drought stress and therefore potentially face long-term reductions in productivity and survival if temperature and aridity increase as predicted for many regions across the globe5,6. Safety margins are largely independent of mean annual precipitation, showing that there is global convergence in the vulnerability of forests to drought, with all forest biomes equally vulnerable to hydraulic failure regardless of their current rainfall environment. These findings provide insight into why drought-induced forest decline is occurring not only in arid regions but also in wet forests not normally considered at drought risk7,8.

• The lack of extant lianescent vessel-less seed plants supports a hypothesis that liana evolution requires large-diameter xylem conduits. Here, we demonstrate an unusual example of a lianoid vessel-less angiosperm, Tasmannia cordata (Winteraceae), from New Guinea. • Wood mechanical, hydraulic and structural measurements were used to determine how T. cordata climbs and to test for ecophysiological shifts related to liana evolution vs 13 free-standing congeners. • The tracheid-based wood of T. cordata furnished low hydraulic capacity compared with that of vessel-bearing lianas. In comparison with most nonclimbing relatives, T. cordata possessed lower photosynthetic rates and leaf and stem hydraulic capacities. However, T. cordata exhibited a two- to five-fold greater wood elastic modulus than its relatives. • Tasmannia cordata provides an unusual example of angiosperm liana evolution uncoupled from xylem conduit gigantism, as well as high plasticity and cell type diversity in vascular development. Because T. cordata lacks vessels, our results suggest that a key limitation for a vessel-less liana is that strong and low hydraulically conductive wood is required to meet the mechanical demands of lianescence.