Fern Lineages Research Articles

Far-Red Light-Induced Azolla filiculoides Symbiosis Sexual Reproduction: Responsive Transcripts of Symbiont Nostoc azollae Encode Transporters Whilst Those of the Fern Relate to the Angiosperm Floral Transition.

Water ferns of the genus Azolla and the filamentous cyanobacteria Nostoc azollae constitute a model symbiosis that enabled the colonization of the water surface with traits highly desirable for the development of more sustainable crops: their floating mats capture CO2 and fix N2 at high rates using light energy. Their mode of sexual reproduction is heterosporous. The regulation of the transition from the vegetative phase to the spore forming phase in ferns is largely unknown, yet a prerequisite for Azolla domestication, and of particular interest as ferns represent the sister lineage of seed plants. Sporocarps induced with far red light could be crossed so as to verify species attribution of strains from the Netherlands but not of the strain from the Anzali lagoon in Iran; the latter strain was assigned to a novel species cluster from South America. Red-dominated light suppresses the formation of dissemination stages in both gametophyte- and sporophyte-dominated lineages of plants, the response likely is a convergent ecological strategy to open fields. FR-responsive transcripts included those from MIKCC homologues of CMADS1 and miR319-controlled GAMYB transcription factors in the fern, transporters in N. azollae, and ycf2 in chloroplasts. Loci of conserved microRNA (miRNA) in the fern lineage included miR172, yet FR only induced miR529 and miR535, and reduced miR319 and miR159. Phylogenomic analyses of MIKCC TFs suggested that the control of flowering and flower organ specification may have originated from the diploid to haploid phase transition in the homosporous common ancestor of ferns and seed plants.

Evolution of genome space occupation in ferns: linking genome diversity and species richness.

The dynamics of genome evolution caused by whole genome duplications and other processes are hypothesized to shape the diversification of plants and thus contribute to the astonishing variation in species richness among the main lineages of land plants. Ferns, the second most species-rich lineage of land plants, are highly suitable to test this hypothesis because of several unique features that distinguish fern genomes from those of seed plants. In this study, we tested the hypothesis that genome diversity and disparity shape fern species diversity by recording several parameters related to genome size and chromosome number. We conducted de novo measurement of DNA C-values across the fern phylogeny to reconstruct the phylogenetic history of the genome space occupation in ferns by integrating genomic parameters such as genome size, chromosome number and average DNA amount per chromosome into a time-scaled phylogenetic framework. Using phylogenetic generalized least square methods, we determined correlations between chromosome number and genome size, species diversity and evolutionary rates of their transformation. The measurements of DNA C-values for 233 species more than doubled the taxon coverage from ~2.2 % in previous studies to 5.3 % of extant diversity. The dataset not only documented substantial differences in the accumulation of genomic diversity and disparity among the major lineages of ferns but also supported the predicted correlation between species diversity and the dynamics of genome evolution. Our results demonstrated substantial genome disparity among different groups of ferns and supported the prediction that alterations of reproductive modes alter trends of genome evolution. Finally, we recovered evidence for a close link between the dynamics of genome evolution and species diversity in ferns for the first time.

Plastid phylogenomics provides novel insights into the infrafamilial relationship of Polypodiaceae.

The polygrammoids (Polypodiaceae) are the most species-rich and diversified epiphytic fern lineages, and hold an important role to understand the deep diverging events and rapid adaptation to changing environments in the plant tree of life. Despite progress in the phylogeny of this group of ferns in previous multilocus phylogenetic studies, uncertainty remains especially in backbone relationships among closely related clades, and the phylogenetic placement of recalcitrant species or lineages. Here, we investigated the deep phylogenetic relationships within Polypodiaceae by sampling all major lineages and using 81 plastid genomes (plastomes), of which 70 plastomes were newly sequenced with high-throughput sequencing technology. Based on parsimony, maximum-likelihood, Bayesian and multispecies coalescent analyses of genome skimming data, we achieved a better resolution of the backbone phylogeny of Polypodiaceae. Using simulated data matrices, we detected that potential phylogenetic artefacts, such as long-branch attraction and insufficient taxonomic sampling, may have a confounding impact on the incongruence of phylogenetic inferences. Furthermore, our phylogenetic analyses offer greater resolution than previous multilocus studies, providing a robust framework for future phylogenetic implications on the subfamilial taxonomy of Polypodiaceae. Our phylogenomic study not only demonstrates the advantage of a character-rich plastome dataset for resolving the recalcitrant lineages that have undergone rapid radiation, but also sheds new light on integrative explorations understanding the evolutionary history of large fern groups in the genomic era.

Evolution of rapid blue-light response linked to explosive diversification of ferns in angiosperm forests.

Summary Ferns appear in the fossil record some 200 Myr before angiosperms. However, as angiosperm‐dominated forest canopies emerged in the Cretaceous period there was an explosive diversification of modern (leptosporangiate) ferns, which thrived in low, blue‐enhanced light beneath angiosperm canopies. A mechanistic explanation for this transformative event in the diversification of ferns has remained elusive.We used physiological assays, transcriptome analysis and evolutionary bioinformatics to investigate a potential connection between the evolution of enhanced stomatal sensitivity to blue light in modern ferns and the rise of angiosperm‐dominated forests in the geological record.We demonstrate that members of the largest subclade of leptosporangiate ferns, Polypodiales, have significantly faster stomatal response to blue light than more ancient fern lineages and a representative angiosperm. We link this higher sensitivity to levels of differentially expressed genes in blue‐light signaling, particularly in the cryptochrome (CRY) signaling pathway. Moreover, CRYs of the Polypodiales examined show gene duplication events between 212.9–196.9 and 164.4–151.8 Ma, when angiosperms were emerging, which are lacking in other major clades of extant land plants.These findings suggest that evolution of stomatal blue‐light sensitivity helped modern ferns exploit the shady habitat beneath angiosperm forest canopies, fueling their Cretaceous hyperdiversification.

On the spore ornamentation of the microsoroid ferns (microsoroideae, polypodiaceae)

Microsoroideae is the third largest of the six subfamilies of Polypodiaceae, containing over 180 species. These ferns are widely distributed in the tropical and subtropical regions of the Old World and Oceania. We documented the spore ornamentation and integrated these data into the latest phylogenetic hypotheses, including a sampling of 100 taxa representing each of 17 major lineages of microsoroid ferns. This enabled us to reconstruct the ancestral states of the spore morphology. The results show verrucate ornamentation as an ancestral state for Goniophlebieae and Lecanoptereae, globular for Microsoreae, and rugulate surface for Lepisoreae. In addition, spore ornamentation can be used to distinguish certain clades of the microsoroid ferns. Among all five tribes, Lecanoptereae show most diversity in spore surface ornamentation.

An updated phylogenetic bioregionalization for the European fern flora

Biogeographic regions have been extensively used as reference units in macroecological studies and to prioritize biodiversity conservation efforts. However, classical bioregionalizations were delineated based on taxonomical similarity across space, and thus the importance of historical factors may have been underrated. This limitation may be particularly relevant for lineages with long and complex evolutionary histories, such as ferns. Here, we drew on an exhaustive distribution dataset including all fern species and subspecies of Europe (661 grid-cells of c. 110 × 110 km each), as well as a nearly complete molecular phylogeny to define fern phyloregions based on their phylogenetic relatedness. Also, we quantified the degree of specificity of individual phylogenetic clades to the phyloregions using a new index of geographical confinement based on phylogenetic diversity. Six distinct phyloregions were identified, with a primary divide between north-eastern and south-western Europe. Both phylogenetic beta diversity and clade specificity were overall low, supporting the idea that dispersal limitation is not a major driver of fern distribution. Yet, the phylogenetic specificity analysis revealed that ancient fern lineages show preference for northern latitudes, which explained the northeast to southwest split of the territory. More than 40 years after the only bioregionalization analysis for the European fern flora, our study provides a fresh regional delineation that takes into account the evolutionary history of the group. In addition to classical bioregionalization approaches, our phylogenetic specificity index allowed us to elucidate the identity of the clades that ultimately shaped the bioregions, which might otherwise had remained obscure.

Polycyclic solenostele–a new synapomorphy for Pteris sect. Litobrochia

The vascular architecture of the stem–the stele–is one of the most well studied topics in pteridology, and has fascinated botanists for more than 200 years. Stelar architecture has attracted much attention, in part, due to its diversity in the fern lineage as well as its use as a stable taxonomic character for circumscribing species, genera, families, or larger informal clades. One aspect of stelar morphology that has garnered specific attention is polystely: the development of multiple concentric cylinders of vasculature. This feature has evolved in lineages throughout the fern phylogeny, including in the genus Pteris L. (Pteridaceae). Here, I describe a polycyclic solenostele as a new synapomorphy for Pteris sect. Litobrochia. The identification of this character as a synapomorphy furthers our understanding of the morphological evolution and circumscription of Pteris as well as aides in species identification within this speciose genus.

Life in the canopy: community trait assessments reveal substantial functional diversity among fern epiphytes.

The expansion of angiosperm-dominated forests in the Cretaceous and early Cenozoic had a profound effect on terrestrial biota by creating novel ecological niches. The majority of modern fern lineages are hypothesized to have arisen in response to this expansion, particularly fern epiphytes that radiated into the canopy. Recent evidence, however, suggests that epiphytism does not correlate with increased diversification rates in ferns, calling into question the role of the canopy habitat in fern evolution. To understand the role of the canopy in structuring fern community diversity, we investigated functional traits of fern sporophytes and gametophytes across a broad phylogenetic sampling on the island of Moorea, French Polynesia, including >120 species and representatives of multiple epiphytic radiations. While epiphytes showed convergence in small size and a higher frequency of noncordate gametophytes, they showed greater functional diversity at the community level relative to terrestrial ferns. These results suggest previously overlooked functional diversity among fern epiphytes, and raise the hypothesis that while the angiosperm canopy acted as a complex filter that restricted plant size, it also facilitated diversification into finely partitioned niches. Characterizing these niche axes and adaptations of epiphytic ferns occupying them should be a priority for future pteridological research.

Allopolyploid Speciation Accompanied by Gene Flow in a Tree Fern

Hybridization in plants may result in hybrid speciation or introgression and, thus, is now widely understood to be an important mechanism of species diversity on an evolutionary timescale. Hybridization is particularly common in ferns, as is polyploidy, which often results from hybrid crosses. Nevertheless, hybrid speciation as an evolutionary process in fern lineages remains poorly understood. Here, we employ flow cytometry, phylogeny, genomewide single nucleotide polymorphism data sets, and admixture and coalescent modeling to show that the scaly tree fern, Gymnosphaera metteniana is a naturally occurring allotetraploid species derived from hybridization between the diploids, G.denticulata and G.gigantea. Moreover, we detected ongoing gene flow between the hybrid species and its progenitors, and we found that G.gigantea and G.metteniana inhabit distinct niches, whereas climatic niches of G.denticulata and G.metteniana largely overlap. Taken together, these results suggest that either some degree of intrinsic genetic isolation between the hybrid species and its parental progenitors or ecological isolation over short distances may be playing an important role in the evolution of reproductive barriers. Historical climate change may have facilitated the origin of G.metteniana, with the timing of hybridization coinciding with a period of intensification of the East Asian monsoon during the Pliocene and Pleistocene periods in southern China. Our study of allotetraploid G.metteniana represents the first genomic-level documentation of hybrid speciation in scaly tree ferns and, thus, provides a new perspective on evolution in the lineage.

The complete chloroplast genome of a rare fern species from North China, Botrychium lunaria (Ophioglossaceae)

Species in the genus Botrychium are tiny herbaceous plants with simple morphology that are widely distributed in the northern hemisphere. The phylogenetic relationship intra the genus is not well resolved, different species/populations from North America, Europe, and Asia demonstrate a paraphyletic relationship, including Botrychium lunaria. In this study, we reported the first complete chloroplast genome sequence of B. lunaria from Chinese population. It is 138,558 bp in length, and composed with a typical quadripartite structure. The overall GC content is 44.40%. In total, 129 genes were annotated, including 84 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. A maximum-likelihood tree of primitive fern lineage based on complete chloroplast genome sequence data was constructed. The phylogenetic analysis indicated that Botrychium is closely related to other basal fern lineages, such as Helminthostachys, Ophioglossum, and Mankyua. Furthermore, the genomic data generated in this study will provide helpful information for the conservation of B. lunaria in Beijing, China.

Evolutionary relationships of the ancient fern lineage the adder's tongues (Ophioglossaceae) with description of Sahashia gen. nov.

As an ancient lineage of ferns, Ophioglossaceae are evolutionarily among the most fascinating because they have the highest chromosome count of any known organism as well as the presence of sporophores, subterranean gametophytes, eusporangiate sporangia without annuli, and endophytic fungi. Previous studies have produced conflicting results, identifyingsome lineages with unresolved relationships, and have paid much attention to the subfamily Botrychioideae. But the other species-rich subfamily, Ophioglossoideae, has remained largely understudied and only up to 12 accessions of Ophioglossoideae have been sampled. In this study, DNA sequences of seven plastid markers of 149 accessions (75 in Ophioglossoideae) representing approximately 82 species (approximately 74% of estimated species diversity sensu J. Syst. Evol., 2016, 54, 563) in the family, and two Marattiaceae and two Psilotaceae, are used to infer a phylogeny. Our major results include: (1) Ophioglossaceae are resolved as monophyletic with strong support, and so are all four subfamilies and genera sensu PPG I except Botrypus and Ophioglossum; (2) a new genus Sahashia is segregated from Botrypus so that the monophyly of Botrypus can be retained; (3) the monophyly of Ophioglossum in its current circumscription is uncertain in spite of our large character sampling; (4) there is substantial cryptic speciation in Ophioderma detected by our molecular and morphological study; (5) the recognition of Holubiella is advocated based on its morphology and its sister relationship with Sceptridium; and (6) a novel sister relationship between Botrychium and the JHS clade (Japanobotrychium + (Holubiella+Sceptridium)) is discovered.

An ontogenetic framework for functional studies in the model fern Ceratopteris richardii

As the sister group to seed plants, ferns are a phylogenetically informative lineage. Functional studies in representatives of the fern lineage are helping bridge the knowledge gap in developmental mechanisms between angiosperms and non-vascular plants. The fern life cycle has the advantage of combining a sizable free-living haploid gametophyte, more amenable for developmental studies than the reduced seed plant gametophyte, with an indeterminate and complex diploid sporophyte. Ceratopteris richardii has long been proposed as a model fern and has recently become tractable due to stable transgenesis and increasing genomic resources, allowing researchers to test explicit questions about gene function in a fern for the first time. As with any model system, a detailed understanding of wild-type morphology and a staged ontogeny are indispensable for the characterization of mutant phenotypes resulting from genetic manipulations. Therefore, the goal of this study is to provide a unified reference ontogeny for this emerging model fern as a tool for comparative evolutionary and developmental studies. It complements earlier research by filling gaps in major stages of development of the haploid gametophyte and diploid sporophyte generations, and provides additional descriptions of the shoot apical meristem and early leaf development. This resource is meant to facilitate not only studies of candidate genes within C. richardii, but also broader ontogenetic comparisons to other model plants.

Assessing Chemical Diversity in Psilotum nudum (L.) Beauv., a Pantropical Whisk Fern That Has Lost Many of Its Fern-Like Characters.

Members of the Psilotales (whisk ferns) have a unique anatomy, with conducting tissues but lacking true leaves and roots. Based on recent phyogenies, these features appear to represent a reduction from a more typical modern fern plant rather than the persistence of ancestral features. In this study, extracts of several Psilotum organs and tissues were analyzed by Gas Chromatography – Mass Spectrometry (GC-MS) and High Performance Liquid Chromatography – Quadrupole Time of Flight – Mass Spectrometry (HPLC-QTOF-MS). Some arylpyrones and biflavonoids had previously been reported to occur in Psilotum and these metabolite classes were found to be prominent constituents in the present study. Some of these were enriched and further characterized by Nuclear Magnetic Resonance (NMR) spectroscopy. HPLC-QTOF-MS and NMR data were searched against an updated Spektraris database (expanded by incorporating over 300 new arylpyrone and biflavonoid spectral records) to aid significantly with peak annotation. Principal Component Analysis (PCA) with combined GC-MS and HPLC-QTOF-MS data sets obtained with several Psilotum organs and tissues indicated a clear separation of the sample types. The principal component scores for below-ground rhizome samples corresponded to the vectors for carbohydrate monomers and dimers and small organic acids. Above-ground rhizome samples had principal component scores closer to the direction of vectors for arylpyrone glycosides and sucrose (which had high concentrations in above-and below-ground rhizomes). The unique position of brown synangia in a PCA plot correlated with the vector for biflavonoid glycosides. Principal component scores for green and yellow synangia correlated with the direction of vectors for arylpyrone glycosides and biflavonoid aglycones. Localization studies with cross sections of above-ground rhizomes, using Matrix-Assisted Laser Desorption/Ionization – Mass Spectrometry (MALDI-MS), provided evidence for a preferential accumulation of arylpyrone glycosides and biflavonoid aglycones in cells of the chlorenchyma. Our results indicate a differential localization of metabolites with potentially tissue-specific functions in defenses against biotic and abiotic stresses. The data are also a foundation for follow-up work to better understand chemical diversity in the Psilotales and other members of the fern lineage.

Heinrichsia cheilanthoides gen. et sp. nov., a fossil fern in the family Pteridaceae (Polypodiales) from the Cretaceous amber forests of Myanmar

AbstractDivergence time estimates suggest that most clades constituting the fern family Pteridaceae (Polypodiales) were in existence by the Early Cretaceous. However, fossil evidence to corroborate this remains exceedingly rare. Burmese amber is an important source of new information on the radiation of derived fern lineages during the Cretaceous Terrestrial Revolution. This study describes Heinrichsia cheilanthoides gen. et sp. nov., a fern with suggested affinities to Pteridaceae, based on fertile foliage portions preserved in Early Cretaceous (~100 Ma) amber from Myanmar. Heinrichsia cheilanthoides is characterized by a pinnate‐pinnatifid frond that bears apical, marginal sori protected by a pseudoindusium. Sporangia are of the polypod type and contain tetrahedral‐globose, trilete spores with a striate perine. This discovery provides a new calibration point to test and refine molecular clock‐based concepts of the evolutionary history of the Pteridaceae. Heinrichsia cheilanthoides further substantiates the suggestion that the Cretaceous forests of Myanmar were home to a rich fern flora.

Integrative Paleobotany: Affirming the Role of Fossils in Modern Plant Biology—Introduction and Dedication

Integrative Paleobotany: Affirming the Role of Fossils in Modern Plant Biology—Introduction and Dedication

Genetic and morphological identification of a recurrent Dicksonia tree fern hybrid in New Zealand.

Hybridization is common in many ferns and has been a significant factor in fern evolution and speciation. However, hybrids are rare between the approximately 30 species of Dicksonia tree ferns world-wide, and none are well documented. In this study we examine the relationship of a newly-discovered Dicksonia tree fern from Whirinaki, New Zealand, which does not fit the current taxonomy of the three species currently recognized in New Zealand. Our microsatellite genotyping and ddRAD-seq data indicate these plants are F1 hybrids that have formed multiple times between D. fibrosa and D. lanata subsp. lanata. The Whirinaki plants have intermediate morphology between D. fibrosa and D. lanata subsp. lanata and their malformed spores are consistent with a hybrid origin. The Whirinaki plants–Dicksonia fibrosa × D. lanata subsp. lanata–are an example of hybridization between distantly related fern lineages, with the two parent species estimated to have diverged 55–25 mya. Our chloroplast sequencing indicates asymmetric chloroplast inheritance in the Whirinaki morphology with D. lanata subsp. lanata always contributing the chloroplast genome.

A multi‐character analysis of Struthiopteris leads to the rescue of Spicantopsis (Blechnaceae, Polypodiopsida)

The family Blechnaceae is a moderately sized leptosporangiate fern lineage, with 24 genera and around 250 species. Struthiopteris accommodates small to medium‐sized, dimorphic, pinnate species. It is composed of six northern species: S. spicant is distributed in western parts of Europe and North America; S. fallax is endemic to Iceland; S. niponica, S. amabilis and S. castanea are endemic to Japan, and S. hancockii occurs in Japan and Taiwan. Due to the lack of a global review and to its highly interesting geographical distribution, this genus merits further study to clarify its taxonomy, species relationships, and distributional pattern. The present study aims to achieve the following goals: (a) identify and describe morphological characters supporting the taxonomy of Struthiopteris; (b) reconstruct a complete phylogeny for the genus; (c) study the biogeographical history of Struthiopteris at a global scale. The morphological study involved the observation of characters ranging from rhizome scales to spores over 164 individuals. Phylogenies were constructed applying ML and BI techniques over 51 newly produced sequences of three chloroplast markers (rbcL, trnL‐trnF, psbA‐trnH), using the species Blechnidium melanopus and Brainea insignis as closest relatives. For the molecular dating and historical biogeography analyses, we estimated and compared ancestral ranges under several models. Most of the morphological characters led us to discern two groups of species: the S. spicant group (S. spicant, S. fallax, and S. castanea) and the S. niponica group (the remaining species). In our molecular phylogeny, the supposed sister genus Blechnidium always appeared as nested within Struthiopteris, rendering this genus non‐monophyletic. The two groups identified by the morphology appeared as monophyletic clades within Struthiopteris, with the clade S. spicant more closely related to Blechnidium than to the clade S. niponica. For all these reasons, we propose to rescue the now‐disused genus Spicantopsis for the species belonging to the S. niponica group: indeed, this genus was created c. 100 years ago to reunite the same species S. amabilis, S. niponica, and S. hancockii. Our results suggest that all members of this group of genera (Blechnidium, Struthiopteris, Spicantopsis) emerged in East Asia about 85 mya, at a time when Japan was still part of the mainland. It appears that, for most of their history, the members of these genera have been confined to East Asia, with one dispersal to the Americas by an ancestor within Struthiopteris s.str., and additional dispersals to India and the Philippines by Blechnidium melanopus.

Evolution of substrate specificity and fungal symbiosis in filmy ferns (Hymenophyllaceae): a Bayesian approach for ambiguous character state reconstruction

Ferns, as landplants in general, originally form a symbiosis involving Arbuscular Mycorrhizal Fungi (AMF), which are prevalent in habitats directly connected to the soil, including low epiphytic sites, but are largely absent in the high epiphytic habitat. High probabilities of AMF should be expected in chiefly terrestrial lineages whereas truly, fully adapted epiphytic lineages should be lacking fungal endophytes or may have switched to other types of fungi; e.g. Dark Septate Endophytes (DSE), a morphological class of mostly unspecified fungi that is often found in epiphytic ferns and may include potentially symbiotic ascomycetes. We used a Bayesian approach for a comparison of the ambiguous character of preferred substrate with the incompletely known mycorrhization status for an ancient lineage of ferns, the Hymenophyllaceae or filmy ferns. The majority of the analysed 167 species prefers either the saxicolous, terrestrial or epiphytic habitat (differentiated into low and high epiphytic), but there are also many generalists without clear preference. For the whole family Hymenophyllaceae and one of the two main clades of the subfamily Trichomanoidae, the terrestrial habitat and AMF received the highest probability for representing the ancestral state. For the subfamily Hymenophylloidae, the low epiphytic habitat and DSE received the highest probability as ancestral state, whereas that for AMF was very low. The other main clade of the subfamily Trichomanoidae as well as the whole subfamily was found most likely to be originally terrestrial; but in both cases the probability values did not differ much from the values for low epiphytism, with all values around 50 ± 5%. The high epiphytic habitat, which in its present condition is thought to be possible only in angiosperm-dominated vegetation, did not receive high probability to be the ancestral state in any clade. This decouples the evolution of epiphytism in filmy ferns in time from the advent of the angiosperms, which is hypothesized to have triggered the radiation of all other major epiphytic fern lineages.

Culcita remberi sp. nov., an Understory Fern of Cyatheales from the Miocene of Northern Idaho

Premise of research. Excavations at the Clarkia fossil beds in northern Idaho have recovered numerous exceptionally well-preserved plant fossils over the past 45 years. We report on a compression fossil of a fertile frond from a tree fern found at the Emerald Creek locality.Methodology. Intact leaf material was liberated from the substrate by wetting with hydrofluoric acid followed by submersion in a water bath. The lamina was preserved between sheets of acetate and photographed, and fertile pinnules with sporangia were mounted on aluminum stubs and imaged with scanning electron microscopy. Spores were released from sporangia after incubation in Schulz’s solution and treatment with KOH.Pivotal results. The specimen is similar to members of several extant fern lineages, including Hymenophyllaceae, Dennstaedtiaceae, and the tree fern order Cyatheales. It shares with these groups the possession of oblong, marginal sori, although the sori of the specimen are most similar to the cup-shaped sori of Dennstaedtiaceae and the bivalvate sori of Culcitaceae. The fossil also has sporangia, each with a complete, uninterrupted, oblique annulus, which is strongly associated with Culcitaceae.Conclusions. On the basis of its overall lamina morphology and details of the sori and especially the sporangia, we conclude that this specimen belongs to an extinct species of the monogeneric tree fern family Culcitaceae. The occurrence of a tree fern in the temperate plant community of the Miocene Clarkia locality is unexpected but not incompatible with the habitat preferences of this genus, as the two extant species of Culcita are found in montane altitudes and temperate forests elsewhere in the world.

Assessing the evolutionary history of the fern family Dipteridaceae (Gleicheniales) by incorporating both extant and extinct members in a combined phylogenetic study.

Dipteridaceae is a lineage of ferns that has existed from the early Mesozoic and is known for its extensive fossil record. By integrating information from all described extant and extinct genera into a single phylogenetic study, this paper aims to examine the taxonomy of the group on a whole and explore character evolution within the lineage across time. A morphological matrix of 51 characters was developed for 72 species (43 extinct and 29 extant) based on published information. Morphological characters were combined with nucleotide sequences for four chloroplast genes (rbcL, atpA, atpB, and rps4) for extant taxa, and combined parsimony analyses were conducted to infer evolutionary trends in the group. Dipteridaceae was found to be monophyletic and characterized by highly anastomosing minor veins forming a meshwork of areoles with free-included veinlets. Based on our analyses, we recognize six previously described genera (i.e., Goeppertella, Thaumatopteris, Clathropteris, Digitopteris, Dipteris, and Cheiropleuria) and one new genus (i.e., Sewardalea). Fossils currently described as Dictyophyllum, Kenderlykia, Hausmannia, and Protorhipis are ambiguously placed on the tree and are recognized as possibly unnatural morphogenera. Overall, the evolutionary trend in Dipteridaceae has been toward increasing complexity in the venation pattern and laminal fusion. Only the Hausmannia-type frond with dichotomizing primary veins and relatively fused lamina persisted in the later part of the Mesozoic to the present. Within the crown group, we see evidence of re-radiation of frond forms in Dipteris and Cheiropleuria.