I have collected rocks and fossils since I was a kid, but I became interested in fossil plants in particular while an undergraduate at the University of Pennsylvania, working with Hermann Pfefferkorn on Carboniferous floras from the Canadian Arctic. I continued to pursue paleobotany in my graduate work with Kevin Boyce at the University of Chicago, where I studied the evolution of reproductive morphology in fossil and living conifers. I then spent several years as a postdoc at Yale, working with Peter Crane in the School of Forestry and Michael Donoghue in the Department of Ecology and Evolutionary Biology. Before joining the faculty at Stanford, I was a professor in the Ecology and Evolutionary Biology Department at Brown University.
Boards, Advisory Committees, Professional Organizations
Member, Geological Society of America (2005 - Present)
Member, Botanical Society of America (2005 - Present)
Secretary-Treasurer, Paleobotanical Section of the Botanical Society of America (2017 - Present)
PhD, University of Chicago, Paleontology (2010)
BA, University of Pennsylvania, Biochemistry, Geology (2004)
Current Research and Scholarly Interests
I am interested in morphological evolution. I approach this broad topic by investigating how interactions among form, function, and environment have influenced evolutionary patterns in plant reproductive structures over million-year time scales. This approach requires synthesizing information from different disciplines, and my work uses approaches from paleontology, biomechanics, phylogenetics, and biogeography.
- 500 Million Years of Land Plant Evolution
GEOLSCI 139, GEOLSCI 239 (Spr)
- Coevolution of Earth and Life
EARTHSYS 4, GEOLSCI 4 (Aut)
- Independent Studies (3)
- Prior Year Courses
New fossil discoveries illustrate the diversity of past terrestrial ecosystems in New Caledonia.
2021; 11 (1): 18388
New Caledonia was, until recently, considered an old continental island harbouring a rich biota with outstanding Gondwanan relicts. However, deep marine sedimentation and tectonic evidence suggest complete submergence of the island during the latest Cretaceous to the Paleocene. Molecular phylogenies provide evidence for some deeply-diverging clades that may predate the Eocene and abundant post-Oligocene colonisation events. Extinction and colonization biases, as well as survival of some groups in refuges on neighbouring paleo-islands, may have obscured biogeographic trends over long time scales. Fossil data are therefore crucial for understanding the history of the New Caledonian biota, but occurrences are sparse and have received only limited attention. Here we describe five exceptional fossil assemblages that provide important new insights into New Caledonia's terrestrial paleobiota from three key time intervals: prior to the submersion of the island, following re-emergence, and prior to Pleistocene climatic shifts. These will be of major importance for elucidating changes in New Caledonia's floristic composition over time.
View details for DOI 10.1038/s41598-021-97938-5
View details for PubMedID 34526644
Early Cretaceous abietoid Pinaceae from Mongolia and the history of seed scale shedding.
American journal of botany
PREMISE: Seed cones of extant Pinaceae exhibit two mechanisms of seed release. In "flexers" the cone scales remain attached to the central axis, while flexing and separating from each other to release the seeds. In "shedders" scales are shed from the axis, with the seeds either remaining attached to the scale or becoming detached. The early fossil history of Pinaceae from the Jurassic to Early Cretaceous is dominated by flexing seed cones, while the systematic information provided by shedding fossil cones has been overlooked and rarely integrated with data based on compression and permineralized specimens. We describe the earliest and best-documented evidence of a "shedder" seed cone from the Aptian-Albian of Mongolia.METHODS: Lignite samples from Tevshiin Govi locality were disaggregated in water, washed, and dried in air. Fossils were compared to material of extant Pinaceae using LM and CT scans.RESULTS: Lepidocasus mellonae gen. et sp. nov. is characterized by a seed cone that disarticulated at maturity and shed obovate bract-scale complexes that have a distinctive ribbed surface and an abaxial surface covered with abundant trichomes. The ovuliferous scale has ca. 30-40 resin canals, but only scarce xylem near the attachment to the cone axis. Resin vesicles are present in the seed integument. Phylogenetic analysis places Lepidocasus as sister to extant Cedrus within the abietoid grade.CONCLUSIONS: The exquisite preservation of the trichomes in L. mellonae raises questions about their potential ecological function in the cones of fossil and living Pinaceae. Lepidocasus mellonae also shows that a shedding dispersal syndrome, a feature that has often been overlooked, evolved early in the history of Pinaceae during the Early Cretaceous.
View details for DOI 10.1002/ajb2.1713
View details for PubMedID 34458982
- The influence of climate and palaeoclimate on distributions of global conifer clades depends on geographical range size JOURNAL OF BIOGEOGRAPHY 2021
- Omniastrobus gen. nov., an Emsian Plant with Implications for the Evolution of Heterospory in the Early Devonian INTERNATIONAL JOURNAL OF PLANT SCIENCES 2021
- SEROTINY AND THE EVOLUTION OF SEED CONE SIZE IN CUPRESSACEAE CONIFERS INTERNATIONAL JOURNAL OF PLANT SCIENCES 2021
- Reproductive innovations and pulsed rise in plant complexity. Science (New York, N.Y.) 2021; 373 (6561): 1368-1372
A novel reproductive strategy in an Early Devonian plant
2020; 30 (9): R388–R389
View details for Web of Science ID 000530137200008
Accumulation over evolutionary time as a major cause of biodiversity hotspots in conifers
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
2019; 286 (1912): 20191887
Biodiversity hotspots are important for understanding how areas of high species richness form, but disentangling the processes that produce them is difficult. We combine geographical ranges, phylogenetic relationships and trait data for 606 conifer species in order to explore the mechanisms underlying richness hotspot formation. We identify eight richness hotspots that overlap known centres of plant endemism and diversity, and find that conifer richness hotspots occur in mountainous areas within broader regions of long-term climate stability. Conifer hotspots are not unique in their species composition, traits or phylogenetic structure; however, a large percentage of their species are not restricted to hotspots and they rarely show either a preponderance of new radiating lineages or old relictual lineages. We suggest that conifer hotspots have primarily formed as a result of lineages accumulating over evolutionary time scales in stable mountainous areas rather than through high origination, preferential retention of relictual lineages or radiation of species with unique traits, although such processes may contribute to nuanced differences among hotspots. Conifers suggest that a simple accumulation of regional diversity can generate high species richness without additional processes and that geography rather than biology may play a primary role in hotspot formation.
View details for DOI 10.1098/rspb.2019.1887
View details for Web of Science ID 000490551300019
View details for PubMedID 31594500
View details for PubMedCentralID PMC6790781
- Naturalized distributions show that climatic disequilibrium is structured by niche size in pines (Pinus L.) GLOBAL ECOLOGY AND BIOGEOGRAPHY 2019; 28 (4): 429–41
Not all 'pine cones' flex: functional trade-offs and the evolution of seed release mechanisms
2019; 222 (1): 396–407
Seed dispersal is critical for plants, but the evolution of mechanisms that actually release seeds from their parents is not well understood. We use the reproductive cones of conifers, specifically the Pinaceae clade, to explore the factors driving the evolution of different release mechanisms in plants. We combine comparative anatomical and phylogenetic analyses to test whether fundamental trade-offs in the mechanical and hydraulic properties of vasculature underlie the evolution of two seed release mechanisms: cone scale flexion and cone scale shedding. We then test whether these mechanisms are linked with differences in seed size, dispersal syndrome and reproductive allocation. Cone scale xylem in flexing species is tough, but poorly conductive. Xylem in shedding species is less extensive, fragile and highly conductive; its thin-walled tracheids allow scales to easily fracture at maturity. Shedding is also consistently associated with large, densely packed seeds. Pinaceae cones exploit a well-known trade-off in xylem mechanical strength vs hydraulic efficiency to generate release mechanisms that allow seeds of various sizes to leave the protecting cone. The linkage among release mechanisms, vascular anatomy and seed traits illustrates how a wide variety of selective pressures may influence the function and physiology of reproductive structures.
View details for DOI 10.1111/nph.15563
View details for Web of Science ID 000459928400035
View details for PubMedID 30367490
- A phylogenetic analysis of conifer diterpenoids and their carbon isotopes for chemotaxonomic applications ORGANIC GEOCHEMISTRY 2019; 127: 50–58
- Reproductive ontogeny and the evolution of morphological diversity in conifers and other plants INTEGRATIVE AND COMPARATIVE BIOLOGY 2019; 59: 548-558
- Sporangium position, branching architecture, and the evolution of reproductive morphology in Devonian plants INTERNATIONAL JOURNAL OF PLANT SCIENCES 2019; 180: 493-503
Functional diversity and convergence in the evolution of plant reproductive structures
ANNALS OF BOTANY
2019; 123 (1): 145–52
Structures that simultaneously perform many functional roles are likely to show a variety of morphological solutions to these demands, and thus probably exhibit high morphological disparity. In contrast, specialization for a few simple functions should result in a more limited suite of morphologies. We explore this idea using lycopsid reproductive structures, which, throughout their history, have performed a limited set of functional roles compared with the reproductive structures of other plant groups such as seed plants.We scored living and fossil lycopsid taxa for 18 discrete character measurements and several continuous traits, including sporangium size, supporting axis diameter, and strobilus length and width. We used the discrete characters to construct a multivariate morphospace for lycopsid reproductive morphology through time, and the continuous characters to test whether fossil and extant lycopsids show similar patterns of tissue allocation within reproductive structures.Lycopsids occupy similar areas of reproductive morphospace and show similar patterns of tissue allocation over most of their history, alternating between diffuse fertile zones with leaf-like sporophylls and compact strobili with specialized sporophylls that allow sporangia to be closely packed while also protected during their development. Growth habit also plays an important role in lycopsid reproductive evolution, broadly influencing the size and shape of reproductive structures.Lycopsid reproductive structures are primarily specialized for densely packaging sporangia, and are consistent with the idea that performing limited functional roles is associated with reduced morphological disparity. Morphologies similar to lycopsid strobili are also found in other groups with simple, wind-dispersed propagules, suggesting that the same processes occur across plant lineages.
View details for DOI 10.1093/aob/mcy151
View details for Web of Science ID 000462548500013
View details for PubMedID 30107388
View details for PubMedCentralID PMC6344085
An overview of extant conifer evolution from the perspective of the fossil record
AMERICAN JOURNAL OF BOTANY
2018; 105 (9): 1531–44
Conifers are an important living seed plant lineage with an extensive fossil record spanning more than 300 million years. The group therefore provides an excellent opportunity to explore congruence and conflict between dated molecular phylogenies and the fossil record.We surveyed the current state of knowledge in conifer phylogenetics to present a new time-calibrated molecular tree that samples ~90% of extant species diversity. We compared phylogenetic relationships and estimated divergence ages in this new phylogeny with the paleobotanical record, focusing on clades that are species-rich and well known from fossils.Molecular topologies and estimated divergence ages largely agree with the fossil record in Cupressaceae, conflict with it in Araucariaceae, and are ambiguous in Pinaceae and Podocarpaceae. Molecular phylogenies provide insights into some fundamental questions in conifer evolution, such as the origin of their seed cones, but using them to reconstruct the evolutionary history of specific traits can be challenging.Molecular phylogenies are useful for answering deep questions in conifer evolution if they depend on understanding relationships among extant lineages. Because of extinction, however, molecular datasets poorly sample diversity from periods much earlier than the Late Cretaceous. This fundamentally limits their utility for understanding deep patterns of character evolution and resolving the overall pattern of conifer phylogeny.
View details for DOI 10.1002/ajb2.1143
View details for Web of Science ID 000444797500010
View details for PubMedID 30157290
Why are the seed cones of conifers so diverse at pollination?
ANNALS OF BOTANY
2018; 121 (7): 1319–31
Form and function relationships in plant reproductive structures have long fascinated biologists. Although the intricate associations between specific pollinators and reproductive morphology have been widely explored among animal-pollinated plants, the evolutionary processes underlying the diverse morphologies of wind-pollinated plants remain less well understood. Here we study how this diversity may have arisen by focusing on two conifer species in the pine family that have divergent reproductive cone morphologies at pollination.Standard histology methods, artificial wind pollination assays and phylogenetic analyses were used in this study.A detailed study of cone ontogeny in these species reveals that variation in the rate at which their cone scales mature means that pollination occurs at different stages in their development, and thus in association with different specific morphologies. Pollination experiments nevertheless indicate that both species effectively capture pollen.In wind-pollinated plants, morphological diversity may result from simple variation in development among lineages rather than selective pressures for any major differences in function or performance. This work also illustrates the broader importance of developmental context in understanding plant form and function relationships; because plant reproductive structures perform many different functions over their lifetime, subtle differences in development may dramatically alter the specific morphologies that they use to meet these demands.
View details for DOI 10.1093/aob/mcy029
View details for Web of Science ID 000434870300012
View details for PubMedID 29528365
View details for PubMedCentralID PMC6007286
- Leaves of Podozamites and Pseudotorellia from the Early Cretaceous of Mongolia: stomatal patterns and implications for relationships JOURNAL OF SYSTEMATIC PALAEONTOLOGY 2018; 16 (2): 111–37
Araucaria bract-scale complex and associated foliage from the early-middle Eocene of Antarctica and their implications for Gondwanan biogeography
View details for DOI 10.1080/08912963.2018.1472255
Variation in seed size is structured by dispersal syndrome and cone morphology in conifers and other nonflowering seed plants
2017; 216 (2): 429–37
Seed size varies tremendously in plants and its evolution is influenced by multiple ecological and biological factors that are difficult to disentangle. In this study, we focus on understanding the role of seed dispersal by animals in the evolution of seed size in conifers, the most diverse extant nonflowering seed plant group. Relationships among seed size, dispersal syndrome, climate and cone morphology were analyzed across conifers using quantitative models of character evolution and phylogenetic regression techniques. Dispersal syndrome is a more consistent predictor of seed size within major extant conifer clades than climate. Seeds are generally larger in animal-dispersed than wind-dispersed species, and particular cone morphologies are consistently associated with specific ranges in seed size. Seed size and cone morphology evolve in a correlated manner in many animal-dispersed conifers, following a trade-off that minimizes the total size of the dispersal unit. These relationships are also present in other nonflowering seed plant groups, and have been important in the evolution of seeds and cones at least over the Cenozoic and perhaps over much of the later Mesozoic.
View details for DOI 10.1111/nph.14456
View details for Web of Science ID 000427294000013
View details for PubMedID 28185279
Fossils matter: improved estimates of divergence times in Pinus reveal older diversification
BMC EVOLUTIONARY BIOLOGY
2017; 17: 95
The taxonomy of pines (genus Pinus) is widely accepted and a robust gene tree based on entire plastome sequences exists. However, there is a large discrepancy in estimated divergence times of major pine clades among existing studies, mainly due to differences in fossil placement and dating methods used. We currently lack a dated molecular phylogeny that makes use of the rich pine fossil record, and this study is the first to estimate the divergence dates of pines based on a large number of fossils (21) evenly distributed across all major clades, in combination with applying both node and tip dating methods.We present a range of molecular phylogenetic trees of Pinus generated within a Bayesian framework. We find the origin of crown Pinus is likely up to 30 Myr older (Early Cretaceous) than inferred in most previous studies (Late Cretaceous) and propose generally older divergence times for major clades within Pinus than previously thought. Our age estimates vary significantly between the different dating approaches, but the results generally agree on older divergence times. We present a revised list of 21 fossils that are suitable to use in dating or comparative analyses of pines.Reliable estimates of divergence times in pines are essential if we are to link diversification processes and functional adaptation of this genus to geological events or to changing climates. In addition to older divergence times in Pinus, our results also indicate that node age estimates in pines depend on dating approaches and the specific fossil sets used, reflecting inherent differences in various dating approaches. The sets of dated phylogenetic trees of pines presented here provide a way to account for uncertainties in age estimations when applying comparative phylogenetic methods.
View details for DOI 10.1186/s12862-017-0941-z
View details for Web of Science ID 000398227700002
View details for PubMedID 28376717
View details for PubMedCentralID PMC5381128
- Ancient islands acted as refugia and pumps for conifer diversity CLADISTICS 2017; 33 (1): 69–92
- Cupressaceae Conifers from the Early Cretaceous of Mongolia INTERNATIONAL JOURNAL OF PLANT SCIENCES 2017; 178 (1): 19–41
- A new Cheirolepidaceae (Coniferales) from the Early Jurassic of Patagonia (Argentina): reconciling the records of impression and permineralized fossils AMERICAN JOURNAL OF BOTANY 2017; 104: 322-334
Early Cretaceous Umkomasia from Mongolia: implications for homology of corystosperm cupules
2016; 210 (4): 1418–29
Corystosperms, a key extinct group of Late Permian to Early Cretaceous plants, are important for understanding seed plant phylogeny, including the evolution of the angiosperm carpel and anatropous bitegmic ovule. Here, we describe a new species of corystosperm seed-bearing organ, Umkomasia mongolica sp. nov., based on hundreds of three-dimensionally preserved mesofossils from the Early Cretaceous of Mongolia. Individual seed-bearing units of U. mongolica consist of a bract subtending an axis that bifurcates, with each fork (cupule stalk) bearing a cupule near the tip. Each cupule is formed by the strongly reflexed cupule stalk and two lateral flaps that partially enclose an erect seed. The seed is borne at, or close to, the tip of the reflexed cupule stalk, with the micropyle oriented towards the stalk base. The corystosperm cupule is generally interpreted as a modified leaf that bears a seed on its abaxial surface. However, U. mongolica suggests that an earlier interpretation, in which the seed is borne directly on an axis (shoot), is equally likely. The 'axial' interpretation suggests a possible relationship of corystosperms to Ginkgo. It also suggests that the cupules of corystosperms may be less distinct from those of Caytonia than has previously been supposed.
View details for DOI 10.1111/nph.13871
View details for Web of Science ID 000379211400025
View details for PubMedID 26840646
- New fossil Pinaceae from the Early Cretaceous of Mongolia BOTANY 2016; 94: 885-915
- Leaf wax composition and carbon isotopes vary among major conifer groups GEOCHIMICA ET COSMOCHIMICA ACTA 2015; 170: 145–56
- A New Voltzian Seed Cone from the Early Cretaceous of Mongolia and Its Implications for the Evolution of Ancient Conifers INTERNATIONAL JOURNAL OF PLANT SCIENCES 2015; 176 (8): 791–809
Integration and macroevolutionary patterns in the pollination biology of conifers
2015; 69 (6): 1573–83
Integration influences patterns of trait evolution, but the relationship between these patterns and the degree of trait integration is not well understood. To explore this further, we study a specialized pollination mechanism in conifers whose traits are linked through function but not development. This mechanism depends on interactions among three characters: pollen that is buoyant, ovules that face downward at pollination, and the production of a liquid droplet that buoyant grains float through to enter the ovule. We use a well-sampled phylogeny of conifers to test correlated evolution among these characters and specific sequences of character change. Using likelihood models of character evolution, we find that pollen morphology and ovule characters evolve in a concerted manner, where the flotation mechanism breaks down irreversibly following changes in orientation or drop production. The breakdown of this functional constraint, which may be facilitated by the lack of developmental integration among the constituent traits, is associated with increased trait variation and more diverse pollination strategies. Although this functional "release" increases diversity in some ways, the irreversible way in which the flotation mechanism is lost may eventually result in its complete disappearance from seed plant reproductive biology.
View details for DOI 10.1111/evo.12670
View details for Web of Science ID 000356675400016
View details for PubMedID 25903435
- WHOLE-PLANT RECONSTRUCTION AND PHYLOGENETIC RELATIONSHIPS OF ELATIDES ZHOUI SP NOV (CUPRESSACEAE) FROM THE EARLY CRETACEOUS OF MONGOLIA INTERNATIONAL JOURNAL OF PLANT SCIENCES 2014; 175 (8): 911–30
Cone size is related to branching architecture in conifers
2014; 203 (4): 1119–27
The relationship between branch diameter and leaf size has been widely used to understand how vegetative resources are allocated in plants. Branching architecture influences reproductive allocation as well, but fewer studies have explored this relationship at broad phylogenetic or ecological scales. In this study, we tested whether pollen-producing and seed-producing cone size scales with branch diameter in conifers, a diverse and globally distributed lineage of nonflowering seed plants. Branch diameter and cone size were analyzed using multiple regression models and evolutionary models of trait evolution for a data set of 293 extant conifer species within an explicit phylogenetic framework. Branch diameter is a strong predictor of cone size across conifer species, particularly for pollen cones and dry seed cones. However, these relationships are complex in detail because leaf morphology and seed dispersal biology influence the specific ways in which they are expressed. The ubiquity and strength of these scaling relationships across conifers suggest that reproductive and vegetative morphologies are coupled in the group, and it is therefore difficult to disentangle the evolution of cone size from the evolution of branching architecture.
View details for DOI 10.1111/nph.12864
View details for Web of Science ID 000340286000012
View details for PubMedID 24889934
- Major Events in the Evolution of Land Plants Princeton Guide to Evolution 2014: 143–151
PINACEAE-LIKE REPRODUCTIVE MORPHOLOGY IN SCHIZOLEPIDOPSIS CANICULARIS SP NOV FROM THE EARLY CRETACEOUS (APTIAN-ALBIAN) OF MONGOLIA
AMERICAN JOURNAL OF BOTANY
2013; 100 (12): 2426–36
Seed cone scales assigned to the genus Schizolepidopsis are widespread in Late Triassic to Cretaceous Eurasian deposits. They have been linked to the conifer family Pinaceae based on associated vegetative remains, but their exact affinities are uncertain. Recently discovered material from the Early Cretaceous of Mongolia reveals important new information concerning Schizolepidopsis cone scales and seeds, and provides support for a relationship between the genus and extant Pinaceae.Specimens were collected from Early Cretaceous (probable Aptian-Albian) lignite deposits in central Mongolia. Lignite samples were disaggregated, cleaned in hydrofluoric acid, and washed in water. Specimens were selected for further study using light and electron microscopy.Schizolepidopsis canicularis seed cones consist of loosely arranged, bilobed ovulate scales subtended by a small bract. A single inverted seed with an elongate micropyle is borne on each lobe of the ovulate scale. Each seed has a wing formed by the separation of the adaxial surface of the ovulate scale.Schizolepidopsis canicularis produced winged seeds that formed in a manner that is unique to Pinaceae among extant conifers. We do not definitively place this species in Pinaceae pending more complete information concerning its pollen cones and vegetative remains. Nevertheless, this material suggests that Schizolepidopsis may be important for understanding the early evolution of Pinaceae, and may potentially help reconcile the appearance of the family in the fossil record with results based on phylogenetic analyses of molecular data.
View details for DOI 10.3732/ajb.1300173
View details for Web of Science ID 000328255400012
View details for PubMedID 24285570
Explaining the distribution of breeding and dispersal syndromes in conifers
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
2013; 280 (1770): 20131812
The evolution of plants exhibiting different sexes, or dioecy, is correlated with a number of ecological and life-history traits such as woody growth form and animal-dispersed seeds, but the underlying causes of these associations are unclear. Previous work in seed plants has suggested that the evolution of fleshy cones or seeds may favour dioecy. In this study, we use a well-sampled molecular phylogeny of conifers to show that although dioecy and fleshiness strongly co-occur at the species level, this relationship has not resulted from numerous separate origins of this trait combination or from differential rates of diversification. Instead, we suggest that two character combinations-the ancestral dry-monoecious condition and the derived fleshy-dioecious condition-have persisted in conifers longer than other combinations over evolutionary time. The persistence of these trait combinations appears to reflect differences in the rate of successful transition into and out of these character states over time, as well as the geographical restriction of species with rare combinations and their consequent vulnerability to extinction. In general, we argue that such persistence explanations should be considered alongside 'key innovation' hypotheses in explaining the phylogenetic distribution of traits.
View details for DOI 10.1098/rspb.2013.1812
View details for Web of Science ID 000330323300010
View details for PubMedID 24026822
View details for PubMedCentralID PMC3779333
Hemisphere-scale differences in conifer evolutionary dynamics
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2012; 109 (40): 16217–21
Fundamental differences in the distribution of oceans and landmasses in the Northern and Southern Hemispheres potentially impact patterns of biological diversity in the two areas. The evolutionary history of conifers provides an opportunity to explore these dynamics, because the majority of extant conifer species belong to lineages that have been broadly confined to the Northern or Southern Hemisphere during the Cenozoic. Incorporating genetic information with a critical review of fossil evidence, we developed an age-calibrated phylogeny sampling ∼80% of living conifer species. Most extant conifer species diverged recently during the Neogene within clades that generally were established during the later Mesozoic, but lineages that diversified mainly in the Southern Hemisphere show a significantly older distribution of divergence ages than their counterparts in the Northern Hemisphere. Our tree topology and divergence times also are best fit by diversification models in which Northern Hemisphere conifer lineages have higher rates of species turnover than Southern Hemisphere lineages. The abundance of recent divergences in northern clades may reflect complex patterns of migration and range shifts during climatic cycles over the later Neogene leading to elevated rates of speciation and extinction, whereas the scattered persistence of mild, wetter habitats in the Southern Hemisphere may have favored the survival of older lineages.
View details for DOI 10.1073/pnas.1213621109
View details for Web of Science ID 000309611400057
View details for PubMedID 22988083
View details for PubMedCentralID PMC3479534
Branching habit and the allocation of reproductive resources in conifers
ANNALS OF BOTANY
2012; 110 (4): 915–21
Correlated relationships between branch thickness, branch density, and twig and leaf size have been used extensively to study the evolution of plant canopy architecture, but fewer studies have explored the impact of these relationships on the allocation of reproductive resources. This study quantifies pollen cone production in conifers, which have similar basic reproductive biology but vary dramatically in branching habit, in order to test how differences in branch diameter influence pollen cone size and the density with which they are deployed in the canopy.Measurements of canopy branch density, the number of cones per branch and cone size were used to estimate the amount of pollen cone tissues produced by 16 species in three major conifer clades. The number of pollen grains produced was also estimated using direct counts from individual pollen cones.The total amount of pollen cone tissues in the conifer canopy varied little among species and clades, although vegetative traits such as branch thickness, branch density and pollen cone size varied over several orders of magnitude. However, branching habit controls the way these tissues are deployed: taxa with small branches produce small pollen cones at a high density, while taxa with large branches produce large cones relatively sparsely.Conifers appear to invest similar amounts of energy in pollen production independent of branching habit. However, similar associations between branch thickness, branch density and pollen cone size are seen across conifers, including members of living and extinct groups not directly studied here. This suggests that reproductive features relating to pollen cone size are in large part a function of the evolution of vegetative morphology and branching habit.
View details for DOI 10.1093/aob/mcs150
View details for Web of Science ID 000308016100017
View details for PubMedID 22782240
View details for PubMedCentralID PMC3423808
- THE PALEONTOLOGICAL CONTEXT OF ANGIOSPERM VEGETATIVE EVOLUTION INTERNATIONAL JOURNAL OF PLANT SCIENCES 2012; 173 (6): 561-568
- OVULE FUNCTION AND THE EVOLUTION OF ANGIOSPERM REPRODUCTIVE INNOVATIONS INTERNATIONAL JOURNAL OF PLANT SCIENCES 2012; 173 (6): 640-648
Predation and protection in the macroevolutionary history of conifer cones
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
2011; 278 (1720): 3003–8
Conifers are an excellent group in which to explore how changing ecological interactions may have influenced the allocation of reproductive tissues in seed plants over long time scales, because of their extensive fossil record and their important role in terrestrial ecosystems since the Palaeozoic. Measurements of individual conifer pollen-producing and seed-producing cones from the Pennsylvanian to the Recent show that the relative amount of tissue invested in pollen cones has remained constant through time, while seed cones show a sharp increase in proportional tissue investment in the Jurassic that has continued to intensify to the present day. Since seed size in conifers has remained similar through time, this increase reflects greater investment in protective cone tissues such as robust, tightly packed scales. This shift in morphology and tissue allocation is broadly concurrent with the appearance of new vertebrate groups capable of browsing in tree canopies, as well as a diversification of insect-feeding strategies, suggesting that an important change in plant-animal interactions occurred over the Mesozoic that favoured an increase in seed cone protective tissues.
View details for DOI 10.1098/rspb.2010.2648
View details for Web of Science ID 000294244900020
View details for PubMedID 21345864
View details for PubMedCentralID PMC3151706
- Shifting functional roles and the evolution of conifer pollen-producing and seed-producing cones PALEOBIOLOGY 2011; 37 (4): 587–602
- Fossil floras from the Emma Fiord Formation (Visean, Mississippian) of the Canadian Arctic Archipelago and their paleoenvironmental context REVIEW OF PALAEOBOTANY AND PALYNOLOGY 2010; 159 (3-4): 195–203
Flotation preferentially selects saccate pollen during conifer pollination
2010; 188 (1): 273–79
• Among many species of living conifers the presence of pollen with air bladders (saccate pollen) is strongly associated with downward-facing ovules and the production of pollination drops. This combination of features enables saccate pollen grains captured in the pollination drop to float upwards into the ovule. Despite the importance of this mechanism in understanding reproduction in living conifers and in extinct seed plants with similar morphologies, experiments designed to test its effectiveness have yielded equivocal results. • In vitro and in vivo pollination experiments using saccate and nonsaccate pollen were performed using modeled ovules and two Pinus species during their natural pollination period. • Buoyant saccate pollen readily floated through aqueous droplets, separating these grains from nonbuoyant pollen and spores. Ovules that received saccate pollen, nonsaccate pollen or a mixture of both all showed larger amounts and higher proportions of saccate pollen inside ovules after drop secretion. • These results demonstrate that flotation is an effective mechanism of pollen capture and transport in gymnosperms, and suggest that the prevalence of saccate grains and downward-facing ovules in the evolutionary history of seed plants is a result of the widespread use of this mechanism.
View details for DOI 10.1111/j.1469-8137.2010.03356.x
View details for Web of Science ID 000281551500026
View details for PubMedID 20579290
- Upatoia barnardii gen. et sp nov., an araucarian pollen cone with in situ pollen from the Late Cretaceous (Santonian) of Georgia, USA GRANA 2009; 48 (2): 128–35
- INTERPRETING THE FUNCTION OF SACCATE POLLEN IN ANCIENT CONIFERS AND OTHER SEED PLANTS INTERNATIONAL JOURNAL OF PLANT SCIENCES 2008; 169 (8): 1038–45