Large-scale phylogenomic analysis resolves a backbone phylogeny in ferns.

Background: Ferns, originated about 360 million years ago, are the sister group of seed plants. Despite the remarkable progress in our understanding of fern phylogeny, with conflicting molecular evidence and different morphological interpretations, relationships among major fern lineages remain controversial. Results: With the aim to obtain a robust fern phylogeny, we carried out a large-scale phylogenomic analysis using high-quality transcriptome sequencing data, which covered 69 fern species from 38 families and 11 orders. Both coalescent-based and concatenation-based methods were applied to both nucleotide and amino acid sequences in species tree estimation. The resulting topologies are largely congruent with each other, except for the placement of Angiopteris fokiensis, Cheiropleuria bicuspis, Diplaziopsis brunoniana, Matteuccia struthiopteris, Elaphoglossum mcclurei, and Tectaria subpedata. Conclusions: Our result confirmed that Equisetales is sister to the rest of ferns, and Dennstaedtiaceae is sister to eupolypods. Moreover, our result strongly supported some relationships different from the current view of fern phylogeny, including that Marattiaceae may be sister to the monophyletic clade of Psilotaceae and Ophioglossaceae; that Gleicheniaceae and Hymenophyllaceae form a monophyletic clade sister to Dipteridaceae; and that Aspleniaceae is sister to the rest of the groups in eupolypods II. These results were interpreted with morphological traits, especially sporangia characters, and a new evolutionary route of sporangial annulus in ferns was suggested. This backbone phylogeny in ferns sets a foundation for further studies in biology and evolution in ferns, and therefore in plants.

A 4000-species dataset provides new insight into the evolution of ferns.

Ferns are the second-most diverse lineage of vascular plants on Earth, yet the best-sampled time-calibrated phylogeny of the group to date includes fewer than 5% of global diversity and was published seven years ago. We present a time-calibrated phylogeny that includes nearly half of extant fern diversity. Our results are evaluated in the context of previous studies and the fossil record, and we develop new hypotheses about the radiation of leptosporangiate ferns. We used sequence data from six chloroplast regions for nearly 4000 species of ferns to generate the most comprehensive phylogeny of the group ever published. We calibrate the phylogeny with twenty-six fossils and use an array of phylogenetic methods to resolve phylogenetic relationships, estimate divergence times, and infer speciation, extinction, and net diversification rates. We infer a mid-late Silurian origin for ferns (including horsetails) and an early Carboniferous origin for leptosporangiate ferns. Most derived fern families appeared in the Cretaceous and persisted for millions of years before rapidly diversifying in the Cenozoic. We find no evidence of differential rates of diversification among terrestrial and epiphytic species. Our findings challenge previous hypotheses on the evolutionary history of ferns and present a new paradigm for their Cenozoic radiation. We estimate earlier divergences for most fern lineages than were reported in previous studies and provide evidence of extended persistence of major fern lineages prior to rapid diversification in the last fifty million years.

Reverse U-to-C editing exceeds C-to-U RNA editing in some ferns - a monilophyte-wide comparison of chloroplast and mitochondrial RNA editing suggests independent evolution of the two processes in both organelles.

BACKGROUND: RNA editing by C-to-U conversions is nearly omnipresent in land plant chloroplasts and mitochondria, where it mainly serves to reconstitute conserved codon identities in the organelle mRNAs. Reverse U-to-C RNA editing in contrast appears to be restricted to hornworts, some lycophytes, and ferns (monilophytes). A well-resolved monilophyte phylogeny has recently emerged and now allows to trace the side-by-side evolution of both types of pyrimidine exchange editing in the two endosymbiotic organelles. RESULTS: Our study of RNA editing in four selected mitochondrial genes show a wide spectrum of divergent RNA editing frequencies including a dominance of U-to-C over the canonical C-to-U editing in some taxa like the order Schizaeales. We find that silent RNA editing leaving encoded amino acids unchanged is highly biased with more than ten-fold amounts of silent C-to-U over U-to-C edits. In full contrast to flowering plants, RNA editing frequencies are low in early-branching monilophyte lineages but increase in later emerging clades. Moreover, while editing rates in the two organelles are usually correlated, we observe uncoupled evolution of editing frequencies in fern mitochondria and chloroplasts. Most mitochondrial RNA editing sites are shared between the recently emerging fern orders whereas chloroplast editing sites are mostly clade-specific. Finally, we observe that chloroplast RNA editing appears to be completely absent in horsetails (Equisetales), the sister clade of all other monilophytes. CONCLUSIONS: C-to-U and U-to-C RNA editing in fern chloroplasts and mitochondria follow disinct evolutionary pathways that are surprisingly different from what has previously been found in flowering plants. The results call for careful differentiation of the two types of RNA editing in the two endosymbiotic organelles in comparative evolutionary studies.

Identification of common horsetail (Equisetum arvense L.; Equisetaceae) using Thin Layer Chromatography versus DNA barcoding.

The global herbal products market has grown in recent years, making regulation of these products paramount for public healthcare. For instance, the common horsetail (Equisetum arvense L.) is used in numerous herbal products, but it can be adulterated with closely related species, especially E. palustre L. that can produce toxic alkaloids. As morphology-based identification is often difficult or impossible, the identification of processed material can be aided by molecular techniques. In this study, we explore two molecular identification techniques as methods of testing the purity of these products: a Thin Layer Chromatography approach (TLC-test) included in the European Pharmacopoeia and a DNA barcoding approach, used in recent years to identify material in herbal products. We test the potential of these methods for distinguishing and identifying these species using material from herbarium collections and commercial herbal products. We find that both methods can discriminate between the two species and positively identify E. arvense. The TLC-test is more cost- and time-efficient, but DNA barcoding is more powerful in determining the identity of adulterant species. Our study shows that, although DNA barcoding presents certain advantages, other established laboratory methods can perform as well or even better in confirming species' identity in herbal products.

Horsetails are the sister group to all other monilophytes and Marattiales are sister to leptosporangiate ferns.

The "Monilophyte" clade comprising ferns, horsetails and whisk ferns receives unequivocal support from molecular data as the sister clade to seed plants. However, the branching order of its earliest emerging lineages, the Equisetales (horsetails), the Marattiales, the Ophioglossales/Psilotales and the large group of leptosporangiate ferns has remained dubious. We investigated the mitochondrial nad2 and rpl2 genes as two new, intron-containing loci for a wide sampling of taxa. We found that both group II introns - nad2i542g2 and rpl2i846g2 - are universally present among monilophytes. Both introns have orthologues in seed plants where nad2i542g2 has evolved into a trans-arrangement. In contrast and despite substantial size extensions to more than 5kb in Psilotum, nad2i542g2 remains cis-arranged in the monilophytes. For phylogenetic analyses, we filled taxonomic gaps in previously investigated mitochondrial (atp1, nad5) and chloroplast (atpA, atpB, matK, rbcL, rps4) loci and created a 9-gene matrix that also included the new mitochondrial nad2 and rpl2 loci. We extended the taxon sampling with two taxa each for all land plant outgroups (liverworts, mosses, hornworts, lycophytes and seed plants) to minimize the risk of phylogenetic artefacts. We ultimately obtained a well-supported molecular phylogeny placing Marattiales as sister to leptosporangiate ferns and horsetails as sister to all remaining monilophytes. In addition, an indel in an exon of the here introduced rpl2 locus independently supports the placement of horsetails. We conclude that under dense taxon sampling, phylogenetic information from a prudent choice of loci is currently superior to character-rich phylogenomic approaches at low taxon sampling. As here shown the selective choice of loci and taxa enabled us to resolve the long-enigmatic diversifications of the earliest monilophyte lineages.

From algae to angiosperms-inferring the phylogeny of green plants (Viridiplantae) from 360 plastid genomes.

BACKGROUND: Next-generation sequencing has provided a wealth of plastid genome sequence data from an increasingly diverse set of green plants (Viridiplantae). Although these data have helped resolve the phylogeny of numerous clades (e.g., green algae, angiosperms, and gymnosperms), their utility for inferring relationships across all green plants is uncertain. Viridiplantae originated 700-1500 million years ago and may comprise as many as 500,000 species. This clade represents a major source of photosynthetic carbon and contains an immense diversity of life forms, including some of the smallest and largest eukaryotes. Here we explore the limits and challenges of inferring a comprehensive green plant phylogeny from available complete or nearly complete plastid genome sequence data. RESULTS: We assembled protein-coding sequence data for 78 genes from 360 diverse green plant taxa with complete or nearly complete plastid genome sequences available from GenBank. Phylogenetic analyses of the plastid data recovered well-supported backbone relationships and strong support for relationships that were not observed in previous analyses of major subclades within Viridiplantae. However, there also is evidence of systematic error in some analyses. In several instances we obtained strongly supported but conflicting topologies from analyses of nucleotides versus amino acid characters, and the considerable variation in GC content among lineages and within single genomes affected the phylogenetic placement of several taxa. CONCLUSIONS: Analyses of the plastid sequence data recovered a strongly supported framework of relationships for green plants. This framework includes: i) the placement of Zygnematophyceace as sister to land plants (Embryophyta), ii) a clade of extant gymnosperms (Acrogymnospermae) with cycads + Ginkgo sister to remaining extant gymnosperms and with gnetophytes (Gnetophyta) sister to non-Pinaceae conifers (Gnecup trees), and iii) within the monilophyte clade (Monilophyta), Equisetales + Psilotales are sister to Marattiales + leptosporangiate ferns. Our analyses also highlight the challenges of using plastid genome sequences in deep-level phylogenomic analyses, and we provide suggestions for future analyses that will likely incorporate plastid genome sequence data for thousands of species. We particularly emphasize the importance of exploring the effects of different partitioning and character coding strategies.

Trends and concepts in fern classification.

BACKGROUND AND AIMS: Throughout the history of fern classification, familial and generic concepts have been highly labile. Many classifications and evolutionary schemes have been proposed during the last two centuries, reflecting different interpretations of the available evidence. Knowledge of fern structure and life histories has increased through time, providing more evidence on which to base ideas of possible relationships, and classification has changed accordingly. This paper reviews previous classifications of ferns and presents ideas on how to achieve a more stable consensus. SCOPE: An historical overview is provided from the first to the most recent fern classifications, from which conclusions are drawn on past changes and future trends. The problematic concept of family in ferns is discussed, with a particular focus on how this has changed over time. The history of molecular studies and the most recent findings are also presented. KEY RESULTS: Fern classification generally shows a trend from highly artificial, based on an interpretation of a few extrinsic characters, via natural classifications derived from a multitude of intrinsic characters, towards more evolutionary circumscriptions of groups that do not in general align well with the distribution of these previously used characters. It also shows a progression from a few broad family concepts to systems that recognized many more narrowly and highly controversially circumscribed families; currently, the number of families recognized is stabilizing somewhere between these extremes. Placement of many genera was uncertain until the arrival of molecular phylogenetics, which has rapidly been improving our understanding of fern relationships. As a collective category, the so-called 'fern allies' (e.g. Lycopodiales, Psilotaceae, Equisetaceae) were unsurprisingly found to be polyphyletic, and the term should be abandoned. Lycopodiaceae, Selaginellaceae and Isoëtaceae form a clade (the lycopods) that is sister to all other vascular plants, whereas the whisk ferns (Psilotaceae), often included in the lycopods or believed to be associated with the first vascular plants, are sister to Ophioglossaceae and thus belong to the fern clade. The horsetails (Equisetaceae) are also members of the fern clade (sometimes inappropriately called 'monilophytes'), but, within that clade, their placement is still uncertain. Leptosporangiate ferns are better understood, although deep relationships within this group are still unresolved. Earlier, almost all leptosporangiate ferns were placed in a single family (Polypodiaceae or Dennstaedtiaceae), but these families have been redefined to narrower more natural entities. CONCLUSIONS: Concluding this paper, a classification is presented based on our current understanding of relationships of fern and lycopod clades. Major changes in our understanding of these families are highlighted, illustrating issues of classification in relation to convergent evolution and false homologies. Problems with the current classification and groups that still need study are pointed out. A summary phylogenetic tree is also presented. A new classification in which Aspleniaceae, Cyatheaceae, Polypodiaceae and Schizaeaceae are expanded in comparison with the most recent classifications is presented, which is a modification of those proposed by Smith et al. (2006, 2008) and Christenhusz et al. (2011). These classifications are now finding a wider acceptance and use, and even though a few amendments are made based on recently published results from molecular analyses, we have aimed for a stable family and generic classification of ferns.

[Sporogenesis and spores of Equisetum bogotense (Equisetaceae) from mountain areas of Colombia]. / Esporogénesis y esporas de Equisetum bogotense (Equisetaceae) de las áreas montañosas de Colombia.

Studies on some reproductive traits in Equisetum species are scarce and valuable to understand species distribution. Therefore, a detailed study of the sporogenesis process and spore development in E. bogotense is presented, with an analysis of the main events during meiosis, maturation of spores, spore wall ultrastructure, orbicules and elaters. Specimens were collected from 500 to 4500 m in Cauca, Colombia. Strobili at different maturation stages were fixed, dehydrated, embedded in resin, and ultra-microtome obtained sections were stained with Toluidine blue. Observations were made with optical microscopy with differential interference contrast illumination technique (DIC), transmission and scanning electron microscopy (TEM and SEM). Ultrathin sections (70-80 microm) for TEM observations were stained with uranyl acetate and lead citrate; while samples for SEM observations, were fixed, dehydrated in 2.2-dimethoxypropane and dried at critical point as in standard methods. Strobili have numerous mature sporangiophores, each one with a peltate structure, the scutellum, bearing five-six sessile sporangia attached to the axis of strobilus by the manubrium. Immature sporocytes (spore mother cells) are tightly packed within the young sporangia. The sporocytes quickly undergo meiosis, by passing the stage of archesporium and give origin to tetrads of spores. The tapetum loses histological integrity during early stages of sporogenesis, intrudes as a plasmodial mass into the cavity of the sporangium, partially surrounding premeiotic sporocytes, and then, tetrads and adult spores. The tapetum disintegrates towards the end of the sporogenesis, leaving spores free within the sporangial cavity. Spores present several cytological changes that allow them to achieve greater size and increase the number of plastids, before reaching the adult stage. Sporoderm includes three layers external to the cytoplasmic membrane of the spore cell, and they are pseudoendospore, exospore and perispore. Viewed with SEM, the exospore is smooth to rugulate, with micro perforations, while the perispore is muriform, rugate, with narrow, delicate, discontinuous, randomly distributed folds delimiting incomplete, irregular areolae, externally covered by of different size, densely distributed orbicules. These orbicules are also found all over the external face and margins of the elaters, while the internal face is smooth and lack orbicules. Viewed with TEM, the exospore is a thick layer of fine granular material, while perispore is a thinner layer of dense, separate orbicules. The elaters are composed by two layers of fibrillar material: an inner layer with longitudinally oriented fibrils and an outer, thicker and less dense layer with fibrils transversely fibrils and abundant, external orbicules. It is suggested that the processes of ontogeny and characters of the sporoderm are relatively constant in Equisetum; however, sporogenesis in E. bogotense is synchronous and this condition has been observed so far only in E. giganteum, a tropical genus also found in Colombia.

Esporogénesis y esporas de Equisetum bogotense (Equisetaceae) de las áreas montañosas de Colombia / Sporogenesis and spores of Equisetum bogotense (Equisetaceae) from mountain areas of Colombia

Studies on some reproductive traits in Equisetum species are scarce and valuable to understand species distribution. Therefore, a detailed study of the sporogenesis process and spore development in E. bogotense is presented, with an analysis of the main events during meiosis, maturation of spores, spore wall ultrastructure, orbicules and elaters. Specimens were collected from 500 to 4 500m in Cauca, Colombia. Strobili at different maturation stages were fixed, dehydrated, embedded in resin, and ultra-microtome obtained sections were stained with Toluidine blue. Observations were made with optical microscopy with differential interference contrast illumination technique (DIC), transmission and scanning electron microscopy (TEM and SEM). Ultrathin sections (70-80μm) for TEM observations were stained with uranyl acetate and lead citrate; while samples for SEM observations, were fixed, dehydrated in 2.2-dimethoxypropane and dried at critical point as in standard methods. Strobili have numerous mature sporangiophores, each one with a peltate structure, the scutellum, bearing five-six sessile sporangia attached to the axis of strobilus by the manubrium. Immature sporocytes (spore mother cells) are tightly packed within the young sporangia. The sporocytes quickly undergo meiosis, by passing the stage of archesporium and give origin to tetrads of spores. The tapetum loses histological integrity during early stages of sporogenesis, intrudes as a plasmodial mass into the cavity of the sporangium, partially surrounding premeiotic sporocytes, and then, tetrads and adult spores. The tapetum disintegrates towards the end of the sporogenesis, leaving spores free within the sporangial cavity. Spores present several cytological changes that allow them to achieve greater size and increase the number of plastids, before reaching the adult stage. Sporoderm includes three layers external to the cytoplasmic membrane of the spore cell, and they are pseudoendospore, exospore and perispore. Viewed with SEM, the exospore is smooth to rugulate, with micro perforations, while the perispore is muriform, rugate, with narrow, delicate, discontinuous, randomly distributed folds delimiting incomplete, irregular areolae, externally covered by of different size, densely distributed orbicules. These orbicules are also found all over the external face and margins of the elaters, while the internal face is smooth and lack orbicules. Viewed with TEM, the exospore is a thick layer of fine granular material, while perispore is a thinner layer of dense, separate orbicules. The elaters are composed by two layers of fibrillar material: an inner layer with longitudinally oriented fibrils and an outer, thicker and less dense layer with fibrils transversely fibrils and abundant, external orbicules. It is suggested that the processes of ontogeny and characters of the sporoderm are relatively constant in Equisetum; however, sporogenesis in E. bogotense is synchronous and this condition has been observed so far only in E. giganteum, a tropical genus also found in Colombia.

Los estudios sobre aspectos reproductivos son escasos en Equisetum. Por eso, hemos realizado un análisis detallado del proceso de esporogénesis, desarrollo de las esporas, ultraestructura de procesos que tienen lugar durante la meiosis, formación de la pared esporal, orbículas y eláteres de E. bogotense, en especímenes procedentes del Cauca, Colombia. Los estudios se efectuaron mediante microscopía fotónica, electrónica de transmisión (TEM) y de barrido (SEM). Los estróbilos llevan numerosos esporangióforos maduros, cada uno con un escutelo peltado, unido al eje del estróbilo por el manubrio y portador de 5-6 esporangios sésiles. Los esporocitos experimentan meiosis dando origen a tétradas de esporas. El tapete pierde la integridad histológica en las primeras etapas de esporogénesis y rodea los esporocitos premeióticos, posteriormente a las tétradas y finalmente las esporas inmaduras, que experimentan cambios citológicos y de tamaño antes de alcanzar la etapa adulta. El esporodermo de las esporas adultas de E. bogotense consiste de seudoendosporio, exosporio y perisporio. Vistos con MEB, el exosporio de las esporas adultas es liso a rugulado con microperforaciones y el perisporio es muriforme, rugado, con pliegues delicados, estrechos, discontinuos, que se distribuyen al azar y delimitan aréolas incompletas. Externamente el perisporio está cubierto por orbículas, que se forman también en la cara externa y los márgenes de los eláteres. Vistos con TEM, el exosporio es una capa de material granular fino y el perisporio, una capa mucho más delgada con orbículas discretas. Los eláteres están formados por dos capas de naturaleza fibrilar, orientadas longitudinalmente y transversalmente. La esporogénesis en E. bogotense es sincrónica, similar a la de E. giganteum, otra especie de distribución tropical que también crece en Colombia.

Complete plastid genomes from Ophioglossum californicum, Psilotum nudum, and Equisetum hyemale reveal an ancestral land plant genome structure and resolve the position of Equisetales among monilophytes.

BACKGROUND: Plastid genome structure and content is remarkably conserved in land plants. This widespread conservation has facilitated taxon-rich phylogenetic analyses that have resolved organismal relationships among many land plant groups. However, the relationships among major fern lineages, especially the placement of Equisetales, remain enigmatic. RESULTS: In order to understand the evolution of plastid genomes and to establish phylogenetic relationships among ferns, we sequenced the plastid genomes from three early diverging species: Equisetum hyemale (Equisetales), Ophioglossum californicum (Ophioglossales), and Psilotum nudum (Psilotales). A comparison of fern plastid genomes showed that some lineages have retained inverted repeat (IR) boundaries originating from the common ancestor of land plants, while other lineages have experienced multiple IR changes including expansions and inversions. Genome content has remained stable throughout ferns, except for a few lineage-specific losses of genes and introns. Notably, the losses of the rps16 gene and the rps12i346 intron are shared among Psilotales, Ophioglossales, and Equisetales, while the gain of a mitochondrial atp1 intron is shared between Marattiales and Polypodiopsida. These genomic structural changes support the placement of Equisetales as sister to Ophioglossales + Psilotales and Marattiales as sister to Polypodiopsida. This result is augmented by some molecular phylogenetic analyses that recover the same relationships, whereas others suggest a relationship between Equisetales and Polypodiopsida. CONCLUSIONS: Although molecular analyses were inconsistent with respect to the position of Marattiales and Equisetales, several genomic structural changes have for the first time provided a clear placement of these lineages within the ferns. These results further demonstrate the power of using rare genomic structural changes in cases where molecular data fail to provide strong phylogenetic resolution.

Flora, life forms and chorotypes of plants of Salok protected area (North Khorassan Province Iran).

Salok protected Area is located in the 37 degrees 15' to 37 degrees 08' of the North latitude and 57 degrees 16' to 57 degrees 06' of East longitude, in West North Esfarayen in North khorassan province. In this research 52 families, 174 genera and 213 species were identified. The largest plant family is Asteraceae (34 species), Poaceae (18 species), Brassicaceae (17 species) and Fabaceae (17 species), respectively. Chief life forms are Hemicryptopytes (49.29%), Therophytes 23.47% and cryptophytes (12.67%). The most of plants chorotype with 62.91% is influenced by Irano-Touranina elements. Among 213 identified species of this region and 15 species endemic of Iran contain 0.87% of total endemic species of Iran's flora.

Equisetum thermale sp. nov. (Equisetales) from the Jurassic San Agustín hot spring deposit, Patagonia: anatomy, paleoecology, and inferred paleoecophysiology.

PREMISE OF THE STUDY: Dated molecular phylogenies suggest a Cenozoic origin for the crown group of Equisetum. but compression fossil equisetaleans that are morphologically indistinguishable from extant Equisetum and recently discovered anatomically preserved examples strongly suggest an earlier Mesozoic initial diversification. METHODS: In situ samples of Equisetum thermale sp. nov. from the Upper Jurassic San Agustín hot spring deposit were collected and studied with the use of polished blocks, thin sections, and light microscopy. KEY RESULTS: Equisetum thermale exhibits all the morphological and anatomical characteristics of the extant crown group Equisetum. It shows a mixture of features present in the two extant subgenera, e.g., superficial stomata typical of subgenus Equisetum allied with infrequently ramifying stems typical of subgenus Hippochaete. This appears to ally E. thermale with the least derived extant species in the genus Equisetum bogotense (sister species to the two subgenera). Its association of hydromorphic and xeromorphic characters allowed it to grow as an emergent aquatic in physically and chemically stressed geothermally influenced wetlands, where it formed dense monospecific stands. Equisetum thermale, because it is preserved in situ with intact anatomy, provides clear paleoecological, biological, plus inferred paleoecophysiological evidence of adaptations known in extant species. CONCLUSIONS: As the earliest unequivocal member of the genus, E. thermale supports the hypothesis of a Mesozoic origin. Its inferred tolerance of a similar range of stresses (e.g., high salinity, alkalinity, and heavy metal concentrations) to that seen in extant Equisetum suggests early evolution and subsequent maintenance of ecophysiological innovations in the genus.

Complete plastome sequences of Equisetum arvense and Isoetes flaccida: implications for phylogeny and plastid genome evolution of early land plant lineages.

BACKGROUND: Despite considerable progress in our understanding of land plant phylogeny, several nodes in the green tree of life remain poorly resolved. Furthermore, the bulk of currently available data come from only a subset of major land plant clades. Here we examine early land plant evolution using complete plastome sequences including two previously unexamined and phylogenetically critical lineages. To better understand the evolution of land plants and their plastomes, we examined aligned nucleotide sequences, indels, gene and nucleotide composition, inversions, and gene order at the boundaries of the inverted repeats. RESULTS: We present the plastome sequences of Equisetum arvense, a horsetail, and of Isoetes flaccida, a heterosporous lycophyte. Phylogenetic analysis of aligned nucleotides from 49 plastome genes from 43 taxa supported monophyly for the following clades: embryophytes (land plants), lycophytes, monilophytes (leptosporangiate ferns + Angiopteris evecta + Psilotum nudum + Equisetum arvense), and seed plants. Resolution among the four monilophyte lineages remained moderate, although nucleotide analyses suggested that P. nudum and E. arvense form a clade sister to A. evecta + leptosporangiate ferns. Results from phylogenetic analyses of nucleotides were consistent with the distribution of plastome gene rearrangements and with analysis of sequence gaps resulting from insertions and deletions (indels). We found one new indel and an inversion of a block of genes that unites the monilophytes. CONCLUSIONS: Monophyly of monilophytes has been disputed on the basis of morphological and fossil evidence. In the context of a broad sampling of land plant data we find several new pieces of evidence for monilophyte monophyly. Results from this study demonstrate resolution among the four monilophytes lineages, albeit with moderate support; we posit a clade consisting of Equisetaceae and Psilotaceae that is sister to the "true ferns," including Marattiaceae.

Molecular phylogeny of horsetails (Equisetum) including chloroplast atpB sequences.

Equisetum is a genus of 15 extant species that are the sole surviving representatives of the class Sphenopsida. The generally accepted taxonomy of Equisetum recognizes two subgenera: Equisetum and Hippochaete. Two recent phylogenetical studies have independently questioned the monophyly of subgenus Equisetum. Here, I use original (atpB) and published (rbcL, trnL-trnF, rps4) sequence data to investigate the phylogeny of the genus. Analyses of atpB sequences give an unusual topology, with E. bogotense branching within Hippochaete. A Bayesian analysis based on all available sequences yields a tree with increased resolution, favoring the sister relationships of E. bogotense with subgenus Hippochaete.

Primary spinal cord oligodendroglioma. Case illustration / Oligodendroglioma primario de la médula espinal. Caso clínico

Spinal cord oligodendrogliomas are rare pathologies of the spinal cord, and their location at conus and/or filum terminale is even rarer. There are only 7 spinal cord oligodendrogliomas reported in the literature. Our case is the eighth spinal cord oligodendrogliomas at this location (AU)

Los oligodendrogliomas de la médula espinal son raros y su localización en el cono medular o del filum terminale son aún menos frecuentes. Sólo hay siete oligodendrogliomas de la médula encontrados en la literatura. Nuestro caso es el octavo oligodendroglioma medular con esta localización (AU)

Incongruence between primary sequence data and the distribution of a mitochondrial atp1 group II intron among ferns and horsetails.

Using DNA sequence data from multiple genes (often from more than one genome compartment) to reconstruct phylogenetic relationships has become routine. Augmenting this approach with genomic structural characters (e.g., intron gain and loss, changes in gene order) as these data become available from comparative studies already has provided critical insight into some long-standing questions about the evolution of land plants. Here we report on the presence of a group II intron located in the mitochondrial atp1 gene of leptosporangiate and marattioid ferns. Primary sequence data for the atp1 gene are newly reported for 27 taxa, and results are presented from maximum likelihood-based phylogenetic analyses using Bayesian inference for 34 land plants in three data sets: (1) single-gene mitochondrial atp1 (exon+intron sequences); (2) five combined genes (mitochondrial atp1 [exon only]; plastid rbcL, atpB, rps4; nuclear SSU rDNA); and (3) same five combined genes plus morphology. All our phylogenetic analyses corroborate results from previous fern studies that used plastid and nuclear sequence data: the monophyly of euphyllophytes, as well as of monilophytes; whisk ferns (Psilotidae) sister to ophioglossoid ferns (Ophioglossidae); horsetails (Equisetopsida) sister to marattioid ferns (Marattiidae), which together are sister to the monophyletic leptosporangiate ferns. In contrast to the results from the primary sequence data, the genomic structural data (atp1 intron distribution pattern) would seem to suggest that leptosporangiate and marattioid ferns are monophyletic, and together they are the sister group to horsetails--a topology that is rarely reconstructed using primary sequence data.

Triploidy in Equisetum subgenus Hippochaete (Equisetaceae, Pteridophyta).

BACKGROUND AND AIMS: The genus Equisetum is cytologically uniform, having a base chromosome number of x = 108. All previously known species and hybrids that have been counted represent diploids with a sporophytic chromosome number of 2n = 216. Biosystematic studies on Equisetum subgenus Hippochaete revealed evidence that triploids occur in nature. The objective of this study was to confirm that triploid plants exist in the natural environment. METHODS: Flow cytometry was used to establish nuclear DNA values and cytological investigations of meiosis were carried out to obtain information on chromosome number and pairing behaviour. KEY RESULTS: Triploidy exists in three morphologically different hybrid taxa. Two of these are morphologically intermediate between a primary diploid hybrid and a parent, while the third apparently combines genomes from all three Central European Hippochaete species. Nuclear 1C DNA values for the four European Hippochaete species range from 21.4-31.6 pg. For the hybrids, the 1C DNA values not only occupy the same range as the species, but their total DNA amounts agree closely with values predicted by adding the 1C DNA values of each parental genome. Chromosome counts confirm diploidy in the species E. hyemale and E. variegatum and in the hybrid E. xtrachyodon (= E. hyemale x E. variegatum). For the triploids (2n approximately 324), cytological information is presented for the first time. CONCLUSIONS: Triploid taxa may have originated by backcrossing or by crossing of a diploid hybrid with an unrelated diploid species. As tetraploid plants are unknown, these crossings probably involve diploid gametophytes that developed from unreduced diplospores. By repeated crossing events or backcrossing, reticulate evolution patterns arise that are similar to those known for a number of ferns and fern allies.

Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants.

Most of the 470-million-year history of plants on land belongs to bryophytes, pteridophytes and gymnosperms, which eventually yielded to the ecological dominance by angiosperms 90 Myr ago. Our knowledge of angiosperm phylogeny, particularly the branching order of the earliest lineages, has recently been increased by the concurrence of multigene sequence analyses. However, reconstructing relationships for all the main lineages of vascular plants that diverged since the Devonian period has remained a challenge. Here we report phylogenetic analyses of combined data--from morphology and from four genes--for 35 representatives from all the main lineages of land plants. We show that there are three monophyletic groups of extant vascular plants: (1) lycophytes, (2) seed plants and (3) a clade including equisetophytes (horsetails), psilotophytes (whisk ferns) and all eusporangiate and leptosporangiate ferns. Our maximum-likelihood analysis shows unambiguously that horsetails and ferns together are the closest relatives to seed plants. This refutes the prevailing view that horsetails and ferns are transitional evolutionary grades between bryophytes and seed plants, and has important implications for our understanding of the development and evolution of plants.