Conifer Families Research Articles

Novel phylogenetic analysis of the Mesozoic common gymnosperm Xenoxylon Gothan reveals close affinity with extant Podocarpaceae (Coniferales)

AbstractFossil wood is one of the crucial proxies for understanding terrestrial vegetation composition and development in the Earth's history. The gymnosperm wood taxon Xenoxylon Gothan is a significant member of the Mesozoic flora. To date, more than 20 species of Xenoxylon have been described. However, its botanical affinities have remained enigmatic ever since it was described, over a century ago. Here we perform a phylogenetic analysis of Xenoxylon to understand the systematic relationship with extant conifers. Data come from four nucleotide regions (trnL‐F, trnK‐matK, rbcL, psbA‐trnH), xylological characters, and biomolecular composition of five extant conifer families; for Xenoxylon, no nucleotide data are available. Using maximum parsimony in Tree Analysis using New Technology, Xenoxylon appeared basal to Araucariaceae in the data set combining genes and xylological characters, whereas Xenoxylon is placed next to Podocarpaceae in the data set combining genes and biomolecular characters. To find a reliable systematic placement of Xenoxylon, a combined data set of genes, xylological and biomolecular characters is analyzed. Our results and interpretations indicate that Xenoxylon is closely related to Podocarpaceae. This first phylogenetic analysis of Xenoxylon fills the knowledge gap of the systematic relationship of this taxon and contributes to a better understanding of the evolution of extant Podocarpaceae.

New record of Brachyoxylon wood from the Lower Cretaceous of Qingyuan, southeastern China and its palaeoclimatic implications

Early Cretaceous was a key period for the evolution of terrestrial ecosystems. In southeastern China, the late Early Cretaceous (Aptian–Albian) floras are relatively well known and characterized by diverse Cheirolepidiaceae, but the early Early Cretaceous floras in southeastern China are poorly known mainly because of the lack of plant fossils. Here we report petrified woods from a new early Early Cretaceous locality in Qingyuan, southern Zhejiang Province, southeastern China. The new fossil woods collected from the Xishantou Formation (earliest Berriasian, earliest Early Cretaceous) are assigned to Brachyoxylon zhejiangense Tian, Zhu, and Wang based on the anatomy of the secondary xylem. The new material of Brachyoxylon zhejiangense from Qingyuan lacks distinct growth rings or resin canals and has mixed type pitting on the radial walls of the tracheids, araucarioid cross-field pitting, and uniseriate rays. It is the earliest record of Brachyoxylon in southeastern China. Brachyoxylon zhejiangense has been regarded as the wood of the extinct conifer family Cheirolepidiceae and grew in arid to semi-arid environments. Evidence also suggests Cheirolepidiaceae played an important role in the vegetation of southeastern China throughout the Early Cretaceous.

Paternal Inheritance of Mitochondrial DNA May Lead to Dioecy in Conifers

In angiosperms cytoplasmic DNA is typically passed on maternally through ovules. Genes in the mtDNA may cause male sterility. When male-sterile (female) cytotypes produce more seeds than cosexuals, they pass on more copies of their mtDNA and will co-occur with cosexuals with a neutral cytotype. Cytoplasmic gynodioecy is a well-known phenomenon in angiosperms, both in wild and crop plants. In some conifer families (e.g. Pinaceae) mitochondria are also maternally inherited. However in some other families (e.g. Taxaceae and Cupressaceae) mtDNA is paternally inherited through the pollen. With paternal mtDNA inheritance, male cytotypes that produce more pollen than cosexuals are expected to co-occur with cosexuals. This is uncharted territory. An ESS model shows that the presence of male cytotypes selects for more female allocation in the cosexual, i.e. for sexual specialisation. An allele that switches sex from male to female can then invade. This leads to rapid loss of the neutral cytotype of the cosexual, fixation of the male cytotype and dioecy with 50% males and 50% females. The models suggest that paternal inheritance of mtDNA facilitates the evolution dioecy. Consistent with this hypothesis the Pinaceae are 100% monoecious, while dioecy is common in the Taxaceae family and in the genus Juniperus (Cupressaceae). However, no reliable data are yet available on both mode of inheritance of mtDNA and gender variation of the same species. When cosexuals benefit from reproductive assurance (high selfing rate, low inbreeding depression, low fertilisation) they maintain themselves next to males and females. This predicted pattern with three sex types present in the same population is observed in conifers in nature.

A multidisciplinary investigation of a mummified Egyptian head and analysis of its associated resinous material from the Salinas Regional Archaeological Museum in Palermo (Sicily)

Among the 70 items donated by the abbot Antonio Pietro Paternostro to the former National Museum of Palermo (now Salinas Regional Archaeological Museum) in 1870, an ancient Egyptian mummified human head stands out. In 2022 the finding was submitted for a multidisciplinary investigation that relied upon non-invasive or minimally invasive approaches. Investigations revealed that this is a possible female head, which was likely subjected to trans-nasal craniotomy, and dated to the Egyptian Graeco-Roman period. The head was packed with an abundant amount of resin which was analysed using thermogravimetric analysis, infrared spectroscopy, and gas chromatography with mass spectrometry. The analysis suggested that the resin was most likely comprised of a natural resin, pitch, or tar, from the Pinaceae family of conifers, and mixed with other materials including a fat, oil, or wax. The use of multiple sample preparation techniques for the chromatographic analysis provided a high level of confidence in the identification of a wide variety of compounds, including a range of himachalene derivatives, which indicate the inclusion of cedar tar or oil.

Efficient purging of deleterious mutations contributes to the survival of a rare conifer.

Cupressaceae is a conifer family rich in plants of horticultural importance, including Cupressus, Chamaecyparis, Juniperus, and Thuja, yet genomic surveys are lacking for this family. Cupressus gigantea, one of the many rare conifers that are threatened by climate change and anthropogenic habitat fragmentation, plays an ever-increasing role in ecotourism in Tibet. To infer how past climate change has shaped the population evolution of this species, we generated a de novo chromosome-scale genome (10.92Gb) and compared the species' population history and genetic load with that of a widespread close relative, C. duclouxiana. Our demographic analyses, based on 83 re-sequenced individuals from multiple populations of the two species, revealed a sharp decline of population sizes during the first part of the Quaternary. However, populations of C. duclouxiana then started to recover, while C. gigantea populations continued to decrease until recently. The total genomic diversity of C. gigantea is smaller than that of C. duclouxiana, but contrary to expectations, C. gigantea has fewer highly and mildly deleterious mutations than C. duclouxiana, and simulations and statistical tests support purifying selection during prolonged inbreeding as the explanation. Our results highlight the evolutionary consequences of decreased population size on the genetic burden of a long-lived endangered conifer with large genome size and suggest that genetic purging deserves more attention in conservation management.

Detailed Seed Cone Morpho-Anatomy Provides New Insights into Seed Cone Origin and Evolution of Podocarpaceae; Podocarpoid and Dacrydioid Clades.

The study of reproductive morphology and trait evolution provides a vital insight to understand the evolutionary history of plants. The conifer family Podocarpaceae has a remarkable diversity of seed cones, with distinct morphology among the genera and with conifers in general. However, we lack a good understanding of the seed cone morpho-anatomy and trait evolution of Podocarpaceae. We investigated detailed seed cone morpho-anatomy using staining and sectioning techniques to clarify the anatomical, morphological diversity and evolution of functional traits. The presence of a fleshy receptaculum is a characteristic feature of both clades. However, species of Retrophyllum, Afrocarpus and some species of Nageia and Podocarpus form a fleshy sarcotesta-like seed coat, lacking a fleshy receptaculum. The ancestral state reconstructions show a shift between and sometimes within the genus. Although both clades demonstrate fleshiness as an ancestral trait, the shift in fleshy structures provides evidence for complex multiple evolutions of fleshy morphologies. These seed cone traits (e.g., fleshiness and size), along with the broad, flattened and well-adapted (leaf dimorphism) foliage in both clades, are largely congruent with efficient light harvesting and bird dispersal. These traits make these two clades well adapted to their environment, when growing in communities including tall and broad-leaved angiosperms (closed-canopy angiosperm forests), compared to other podocarps, making them more successful in achieving a wider distribution and species richness.

In search of lost time: tracing the fossil diversity of Podocarpaceae through the ages

Abstract The Podocarpaceae are a morphologically diverse conifer family that have a cryptic fossil record reported since the Permian. We reviewed the fossil record of Podocarpaceae, tested the affinities of its oldest records using phylogenetic analyses, compiled macrofossil occurrence records, and investigated the diversity, distribution, and morphology of Podocarpaceae through time. We found that Permian, Triassic, and some Jurassic fossils referred to Podocarpaceae should not be placed in the family. Our total-evidence phylogenetic analyses, which sampled all major conifer lineages, recovered the Triassic Rissikia and the Jurassic Nothodacrium as stem-group conifers and the Jurassic Mataia as part of the Araucariales stem group. We further discuss the phylogenetic position of the Mesozoic enigmatic conifers Pararaucaria (Cheirolepidiaceae) and Telemachus (Voltziales), which were recovered most frequently in the conifer stem group. We conclude that the earliest reliable Podocarpaceae occurrences are from the Jurassic of both hemispheres and have scale-like leaves. Most extant genera appear in the fossil record between the Late Cretaceous and the Early Cenozoic. Many extant leaf morphologies appear in the Early Cretaceous, coeval with angiosperm diversification, consistent with the hypothesis that expanded leaves in Podocarpaceae are adaptive responses for light harvesting in angiosperm-dominated environments today.

Early Jurassic silicified woods from Carapace Nunatak, South Victoria Land, Antarctica

The Jurassic vegetation of Antarctica remains poorly known and, while there have been several reports of large fossil trees from that time period across the continent, detailed anatomical studies of their wood are extremely scarce. Here we describe new silicified woods of Early Jurassic (probably Toarcian) age from Carapace Nunatak, South Victoria Land. The genera Agathoxylon and Brachyoxylon are formally recognized for the first time in the Jurassic of Antarctica. The preservation of the woods is imperfect, which is likely explained by the presence in some of the specimens of fungi, whose anatomical structures are described in detail. Combined with previous reports of pollen, leaves, and cones from South and North Victoria Land, these new specimens support the presence of several conifer families in the Early Jurassic floras of the region.

Pseudofrenelopsis dinisii, a new species of the extinct conifer family Cheirolepidiaceae from the probable lower Hauterivian (Cretaceous) of western Portugal

The Cheirolepidiaceae are an extinct family of conifers that was highly diverse during the Mesozoic, particularly at lower latitudes. Cheirolepidiaceous remains assigned to the genera Frenelopsis and Pseudofrenelopsis are very common in the Early Cretaceous floras of Portugal. A new species Pseudofrenelopsis dinisii is described from the Lower Cretaceous sediments (probably lower Hauterivian) of the Santa Susana Formation, at the Vale Cortiço site in the Lusitanian Basin of western Portugal. The new taxon is described based on morphology of the vegetative shoots and cuticular features. Pseudofrenelopsis dinisii consists of leafy shoots with spirally arranged leaves with an attenuate apex that enclose the stem, while leaves of the Brachyphyllum type occur on terminal shoots. The leaf margins bear well-developed trichomes; the stomatal apparatus is deeply sunken and strengthened by papillae, and the cuticle is moderately thick. Like other frenelopsids, P. dinisii displays these and other typically xeromorphic features, but although many other frenelopsids are associated with independent evidence for arid or saline conditions, the palynoflora from the bed with P. dinisii is rich in spores and shows no evidence of marine influence. Pseudofrenelopsis dinisii may represent the non-arid and non-saline end of the wide spectrum of environments occupied by Cheirolepidiaceae; its xeromorphic features may be adaptations to occasional periods of strong water stress. Comparisons with other sequences suggest a trend in the ecological preferences of both Pseudofrenelopsis and Frenelopsis from alluvial and upper deltaic environments before the Albian to saline coastal environments in the Albian and Cenomanian.

Cross-sectioning to the core of conifers: pith anatomy of living Araucariaceae and Podocarpaceae, with comparisons to fossil pith

Summary Pith in woody species fulfills essential roles, from functioning as the first vascular tissue in shoots, to serving as starch storage and facilitating heartwood formation. While the spongy cells of pith may die and be reabsorbed at maturity by some species, the pith persists throughout the lifespan of conifer trees. Pith features and functions of extant conifers have been documented in contemporary studies, and pith anatomy has been described for extinct progymnosperms and coniferous ancestors through fossils. However, up to now, few studies have described the wood anatomy of pith in living conifers and covered only 24 species in four families. Here we describe the pith of 7 genera and 16 species from the previously unstudied conifer families of Araucariaceae and Podocarpaceae, based on stained and unstained cross-sections. Comparisons between pith sections of the same tree in successive years yielded insights into maturation of the conifer pith. Conservative pith characteristics were identified among genera and families. Araucariaceae pith is dissimilar on a familial level, but the genus Araucaria is unified by pith shape and heterocellularity. In contrast, all Podocarpaceae piths develop secondary cracks, and most species have irregularly shaped piths. Beyond our study of similarities and differences of pith in Araucariaceae and Podocarpaceae, a look at pith patterns in the paleobotanical record and further examples in living conifers could increase the understanding of conserved characteristics and pith evolution.

Diversity, Distribution, Systematics and Conservation Status of Podocarpaceae

Among conifer families, Podocarpaceae is the second largest, with amazing diversity and functional traits, and it is the dominant Southern Hemisphere conifer family. However, comprehensive studies on diversity, distribution, systematic and ecophysiological aspects of the Podocarpaceae are sparse. We aim to outline and evaluate the current and past diversity, distribution, systematics, ecophysiological adaptations, endemism, and conservation status of podocarps. We analyzed data on the diversity and distribution of living and extinct macrofossil taxa and combined it with genetic data to reconstruct an updated phylogeny and understand historical biogeography. Podocarpaceae today contains 20 genera and approximately 219 taxa (201 species, 2 subspecies, 14 varieties and 2 hybrids) placed in three clades, plus a paraphyletic group/grade of four distinct genera. Macrofossil records show the presence of more than 100 podocarp taxa globally, dominantly from the Eocene-Miocene. Australasia (New Caledonia, Tasmania, New Zealand, and Malesia) is the hotspot of living podocarps diversity. Podocarps also show remarkable adaptations from broad to scale leaves, fleshy seed cones, animal dispersal, shrubs to large trees, from lowland to alpine regions and rheophyte to a parasite (including the only parasitic gymnosperm-Parasitaxus) and a complex pattern of seed and leaf functional trait evolution.

Exploring the First Appearance of the Main Derived Conifer Families of Gondwana: Evidence Provided by the Triassic Woods from Argentina

Exploring the First Appearance of the Main Derived Conifer Families of Gondwana: Evidence Provided by the Triassic Woods from Argentina

Phylotranscriptomics and evolution of key genes for terpene biosynthesis in Pinaceae.

Pinaceae is the largest family of conifers, dominating forest ecosystems and serving as the backbone of northern, temperate and mountain forests. The terpenoid metabolism of conifers is responsive to pests, diseases, and environmental stress. Determining the phylogeny and evolution of terpene synthase genes in Pinaceae may shed light on early adaptive evolution. We used different inference methods and datasets to reconstruct the Pinaceae phylogeny based on our assembled transcriptomes. We identified the final species tree of Pinaceae by comparing and summarizing different phylogenetic trees. The genes encoding terpene synthase (TPS) and cytochrome P450 proteins in Pinaceae showed a trend of expansion compared with those in Cycas. Gene family analysis revealed that the number of TPS genes decreased while the number of P450 genes increased in loblolly pine. Expression profiles showed that TPSs and P450s were mainly expressed in leaf buds and needles, which may be the result of long-term evolution to protect these two vulnerable tissues. Our research provides insights into the phylogeny and evolution of terpene synthase genes in Pinaceae and offers some useful references for the investigation of terpenoids in conifers.

A new species of Pararaucaria from the Lower Cretaceous of Shandong province (Eastern China): Insights into the evolution of the Cheirolepidiaceae cone

Pararaucaria, a genus of the extinct conifer family Cheirolepidiaceae, was previously identified from permineralized fossils. This genus reflects important changes in the phylogeny and evolutionary biology of Cheirolepidiaceae. We describe a new species of Pararaucaria (Pararaucaria laiyangensis) from the Lower Cretaceous of the Laiyang Formation in Shandong Province, eastern China using standard paleobotanical descriptions and micro-computed tomography techniques. P. laiyangensis consists of small seed cones with helically arranged bract-scale complexes, isolated ovuliferous scales, and associated scale-leaf foliage with obvious cuticle structures. Bract-scale complexes consist of separated bracts and ovuliferous scales with one seed and three distal lobes. Cuticles consist of haplocheilic and monocyclic stomata arranged in longitudinal rows all over the surface. We assigned the phylogenetic relationship of P. laiyangensis within Cheirolepidiaceae based on the parsimony analyses, and highlight the homology of ovuliferous scales in Pararaucaria and Araucaria according to the comparison with ovuliferous scale structures of all major conifers. Moreover, this species increases our understanding of the dominant tree element of the Laiyang fossil forest, providing the first evidence for ovulate cheirolepidiaceous cones in Asia based on the global distribution of Cheirolepidiaceae reproductive organs.

Neontological and paleontological congruence in the evolution of Podocarpaceae (coniferales) reproductive morphology

IntroductionPodocarpaceae are a diverse, primarily tropical conifer family that commonly produce large leaves and highly reduced, fleshy seed cones bearing large seeds. These features may result from relatively recent adaptation to closed-canopy angiosperm forests and bird-mediated seed dispersal, although determining precisely when shifts in leaf and seed cone morphology occurred is difficult due to a sparse fossil record and relatively few surviving deep lineages.MethodsWe compare the fossil record of Podocarpaceae with results from ancestral state reconstruction methods and correlated character models using neontological data and a previously published molecular time-tree.ResultsAncestral state reconstructions suggest that small leaves, small seeds, and multi-seeded cones are ancestral in crown Podocarpaceae, with reduced cones bearing few seeds appearing in the Early Cretaceous and the correlated evolution of large leaves and large seeds occurring from the Late Cretaceous onwards. The exact timing of these shifts based on neontological data alone are poorly constrained, however, and estimates of leaf and seed size are imprecise.DiscussionThe fossil record is largely congruent with results based on the molecular time-tree, but provide important constraints on the range of leaf and seed sizes that were present in Cretaceous Podocarpaceae and the time by which changes in cone morphology and seed size likely occurred. We suggest in particular that reduced seed cones appeared in the Early Cretaceous and are linked to the contemporaneous diversification of small bodied avialans (birds), with shifts to larger seed sizes occurring after the Cretaceous in association with the spread of closed-canopy angiosperm forests.

Occurrence of Brachyoxylon wood from the Upper Jurassic of Beijing, northern China

ABSTRACT The fossil wood genus Brachyoxylon Hollick et Jeffrey, as an important component of Mesozoic palaeoxylogical assemblages, was widely recorded throughout the world. However, Brachyoxylon fossils were rarely documented in China, and were all reported from the Lower Cretaceous. The Upper Jurassic Tuchengzi Formation is one of the most significant horizons for Jurassic petrified wood in northern China. A new fossil wood species, Brachyoxylon yanqingense sp. nov., was described from the Tuchengzi Formation in Yanqing District of Beijing City, northern China. Anatomically, the new species is characterised by having mixed tracheary radial pitting and araucarioid cross-field pitting. The new finding provides a fresh Jurassic record of Brachyoxylon in China and contributes to further understanding the tempo-spatial distribution of Brachyoxylon in Far-East Asia during the Late Mesozoic. As a fossil wood genus, Brachyoxylon has commonly been related to the extinct conifer family Hirmeriellaceae (Cheirolepidiaceae). Together with an analysis on the floral composition of the Tuchengzi Formation, it is proposed that the Hirmeriellaceae was one of the dominant groups of the forest vegetations in this Late Jurassic flora.

A review of the Hirmeriellaceae (Cheirolepidiaceae) wood

Summary The Hirmeriellaceae are an extinct family of Mesozoic conifers. Their foliage has been described in the genera Brachyphyllum, Frenelopsis, Pseudofrenelopsis, etc., while their pollen corresponds to the genus Classopollis, the male cones to e.g. Classostrobus or Tomaxellia and the female scales were named Hirmeriella and Paraucaria, for example. Reproductive structures are necessary for a definite identification of the family. Such fossils are rarely found in connection with mature secondary xylem. As a result, very little is known about the wood anatomy of the Hirmeriellaceae. This work reviews available evidences, either from connections between wood and reproductive structures typical for the Hirmeriellaceae or from associations of such fossils within Mesozoic rocks. Connection cases are rare and are reported only for the Cretaceous and for genera Frenelopsis and Pseudofrenelopsis. Association cases are more numerous; however, they are also poorly distributed in time, being reported mostly from two intervals only, the latest Triassic–earliest Jurassic and the Early Cretaceous. Wood data are also poorly distributed taxonomically with most of them being from the frenelopsids. The fossil genera Agathoxylon, Brachyoxylon, Protocupressinoxylon and Protopodocarpoxylon were used for wood fossils which are more or less safely related to the Hirmeriellaceae. However, only the first two seem to have been rightly used, the first usually for juvenile or small diameter wood, the second for more mature wood. Even if there seems to be a privileged link between Brachyoxylon and the Hirmeriellaceae, it cannot be said to be exclusive.

Phylogeny and evolution of Cupressaceae: Updates on intergeneric relationships and new insights on ancient intergeneric hybridization

After the merger of the former Taxodiaceae and Cupressaceae s.s., currently the conifer family Cupressaceae (sensu lato) comprises seven subfamilies and 32 genera, most of which are important components of temperate and mountainous forests. With the exception of a recently published genus-level phylogeny of gymnosperms inferred from sequence analysis of 790 orthologs, previous phylogenetic studies of Cupressaceae were based mainly on morphological characters or a few molecular markers, and did not completely resolve the intergeneric relationships. In this study, we reconstructed a robust and well-resolved phylogeny of Cupressaceae represented by all 32 genera, using 1944 genes (Orthogroups) generated from transcriptome sequencing. Reticulate evolution analyses detected a possible ancient hybridization that occurred between ancestors of two subclades of Cupressoideae, including Microbiota-Platycladus-Tetraclinis (MPT) and Juniperus-Cupressus-Hesperocyparis-Callitropsis-Xanthocyparis (JCHCX), although both concatenation and coalescent trees are highly supported. Moreover, divergence time estimation and ancestral area reconstruction indicate that Cupressaceae very likely originated in Asia in the Triassic, and geographic isolation caused by continental separation drove the vicariant evolution of the two subfamilies Cupressoideae and Callitroideae in the northern and southern hemispheres, respectively. Evolutionary analyses of some morphological characters suggest that helically arranged linear-acicular leaves and imbricate bract-scale complexes represent ancestral states, and the shift from linear-acicular leaves to scale-like leaves was associated with the shift from helical to decussate arrangement. Our study sheds new light on phylogeny and evolutionary history of Cupressaceae, and strongly suggests that both dichotomous phylogenetic and reticulate evolution analyses be conducted in phylogenomic studies.

The Triassic pollen genus Camerosporites: New morphological and ultrastructural data, revised taxonomy and paleobiogeographical aspects

This paper presents new morphological and ultrastructural data on Camerosporites pollen obtained from a range of microscopy techniques, and uses these (and other) data to emend the taxonomy of the genus, and review aspects of the paleobiology of its parent plants and their significance in conifer evolution. Camerosporites, a circumpolloid genus probably produced by cheirolepids, was most abundant and widely distributed in low to middle latitudes during the Carnian before declining and becoming extinct in the latest Triassic or perhaps Early Jurassic. The Cheirolepidiaceae, a large and diverse family of early conifers, are characterized by their unique combination of pollen attributes including a rimula, polar tenuitates, exinal threads, verrucae, tetrads/dyads, and exinal and sculptural variability. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) images show most C. secatus pollen grains have a clear proximal rimula and some a probable distal rimula. No convincing specimens with two rimulae were seen. Images from focused ion beam scanning electron microscopy (FIBSEM) show that the verrucae are essentially hollow chambers with thickened outer walls and floored by an irregular reticulate-like network of fine, elongated to granular exinal elements. These images suggest C. secatus pollen grains have relatively “primitive” ultrastructure for a circumpolloid – homogenous nexine, (some) granulae in the infratectum, and an indistinct or absent tectum. Camerosporites was able to thrive in the periodically humid Carnian, clearly demonstrating the vegetative organs of its parent plants were able to adapt to a wide range of paleoenvironments. Nevertheless, Camerosporites may have been out-competed for increasingly scarce water resources in the drying Norian-Rhaetian by other producers of circumpolloid pollen and early conifers with distinct pollination strategies possibly related to siphonogamy. We synonymized C. pseudoverrucatus and C. spissus with C. secatus as they are hard to differentiate consistently given their variability and intergrading attributes. We retained C. verrucosus and, tentatively, C. reductiverrucatus and C. hengyangensis. C. reductiverrucatus can plausibly be interpreted as reworked and degraded C. secatus rather than a different species.

Araucariaceous fossil woods from the Upper Triassic Ischigualasto Formation (San Juan Province, Argentina): paleofloristic and paleoclimatic implications

AbstractIn this contribution, fossil woods from the Valle de La Luna Member of the Upper Triassic Ischigualasto Formation at Ischigualasto Provincial Park, San Juan Province, Argentina, are described. The specimens are preserved as silica permineralization in tuffs intercalated with carbonaceous mudstone beds interpreted as distal floodplain facies. The fossil woods were assigned to the new species Agathoxylon argentinum since their anatomy differs from the known Mesozoic Gondwanan species of the genus Agathoxylon. The combination of characters present in the new taxon indicates an affiliation with the conifer family Araucariaceae. Signals of fungal-mediated wood decay were observed, comparable to the activity of basidiomycetes. Spherical structures attached to the walls of the tracheids were recognized and are interpreted as holocarpic chytrid fungi. The growth rings were quantitatively analyzed. Low values of percentage diminution, percentage latewood, and Ring Markedness Index, and a mean percentage skew of +11.5, were obtained, suggesting that the new species was an evergreen gymnosperm. The stratigraphic distribution and taxonomic composition of the Ischigualasto Formation fossil-plant-bearing levels were studied. A vegetation change is recorded in the fossil level bearing Agathoxylon argentinum n. sp., marked by the replacement of the corystosperm genera and a diminution of arboreal corystosperms. This floristic change, in addition to other evidence, indicates humid paleoclimatic conditions for the uppermost part of the Valle de La Luna Member of the Ischigualasto Formation.