Molecular phylogeny of horsetails (Equisetum) including chloroplast atpB sequences

Chloroplast genome structure analysis of Equisetum unveils phylogenetic relationships to ferns and mutational hotspot region

Equisetum is one of the oldest extant group vascular plants and is considered to be the key to understanding vascular plant evolution. Equisetum is distributed almost all over the world and has a high degree of adaptability to different environments. Despite the fossil record of horsetails (Equisetum, Equisetaceae) dating back to the Carboniferous, the phylogenetic relationship of this genus is not well, and the chloroplast evolution in Equisetum remains poorly understood. In order to fill this gap, we sequenced, assembled, and annotated the chloroplast genomes of 12 species of Equisetum, and compared them to 13 previously published vascular plants chloroplast genomes to deeply examine the plastome evolutionary dynamics of Equisetum. The chloroplast genomes have a highly conserved quadripartite structure across the genus, but these chloroplast genomes have a lower GC content than other ferns. The size of Equisetum plastomes ranges from 130,773 bp to 133,684 bp and they encode 130 genes. Contraction/expansion of IR regions and the number of simple sequences repeat regions underlie large genomic variations in size among them. Comparative analysis revealed we also identified 13 divergence hotspot regions. Additionally, the genes accD and ycf1 can be used as potential DNA barcodes for the identification and phylogeny of the genus Equisetum. Twelve photosynthesis-related genes were specifically selected in Equisetum. Comparative genomic analyses implied divergent evolutionary patterns between Equisetum and other ferns. Phylogenomic analyses and molecular dating revealed a relatively distant phylogenetic relationship between Equisetum and other ferns, supporting the division of pteridophyte into Lycophytes, Equisetaceae and ferns. The results show that the chloroplast genome can be used to solve phylogenetic problems within or between Equisetum species, and also provide genomic resources for the study of Equisetum systematics and evolution.

Plastid Genome of Equisetum xylochaetum from the Atacama Desert, Chile and the Relationships of Equisetum Based on Frequently Used Plastid Genes and Network Analysis

The modern pteridophyte genus Equisetum is the only survivor of Sphenopsida, an ancient clade known from the Devonian. This genus, of nearly worldwide distribution, comprises approximately 15 extant species. However, genomic information is limited. In this study, we assembled the complete chloroplast genome of the giant species Equisetum xylochaetum from a metagenomic sequence and compared the plastid genome structure and protein-coding regions with information available for two other Equisetum species using network analysis. Equisetum chloroplast genomes showed conserved traits of quadripartite structure, gene content, and gene order. Phylogenetic analysis based on plastome protein-coding regions corroborated previous reports that Equisetum is monophyletic, and that E. xylochaetum is more closely related to E. hyemale than to E. arvense. Single-gene phylogenetic estimation and haplotype analysis showed that E. xylochaetum belonged to the subgenus Hippochaete. Single-gene haplotype analysis revealed that E. arvense, E. hyemale, E. myriochaetum, and E. variegatum resolved more than one haplotype per species, suggesting the presence of a high diversity or a high mutation rate of the corresponding nucleotide sequence. Sequences from E. bogotense appeared as a distinct group of haplotypes representing the subgenus Paramochaete that diverged from Hippochaete and Equisetum. In addition, the taxa that were frequently located at the joint region of the map were E. scirpoides and E. pratense, suggesting the presence of some plastome characters among the Equiseum subgenera.

Biogeography and genome size evolution of the oldest extant vascular plant genus, Equisetum (Equisetaceae)

BACKGROUND AND AIMS

Extant plant groups with a long fossil history are key elements in understanding vascular plant evolution. Horsetails (Equisetum, Equisetaceae) have a nearly continuous fossil record dating back to the Carboniferous, but their phylogenetic and biogeographic patterns are still poorly understood. We use here the most extensive phylogenetic analysis to date as a framework to evaluate their age, biogeography and genome size evolution.

METHODS

DNA sequences of four plastid loci were used to estimate divergence times and investigate the biogeographic history of all extant species of Equisetum. Flow cytometry was used to study genome size evolution against the framework of phylogenetic relationships in Equisetum.

KEY RESULTS

On a well-supported phylogenetic tree including all extant Equisetum species, a molecular clock calibrated with multiple fossils places the node at which the outgroup and Equisetum diverged at 343 Mya (Early Carboniferous), with the first major split among extant species occurring 170 Mya (Middle Jurassic). These dates are older than those reported in some other recent molecular clock studies but are largely in agreement with a timeline established by fossil appearance in the geological record. Representatives of evergreen subgenus Hippochaete have much larger genome sizes than those of deciduous subgenus Equisetum, despite their shared conserved chromosome number. Subgenus Paramochaete has an intermediate genome size and maintains the same number of chromosomes.

CONCLUSIONS

The first divergences among extant members of the genus coincided with the break-up of Pangaea and the resulting more humid, warmer climate. Subsequent tectonic activity most likely involved vicariance events that led to species divergences combined with some more recent, long-distance dispersal events. We hypothesize that differences in genome size between subgenera may be related to the number of sperm flagellae.

HILIC HPLC-ESI-MS/MS identification and quantification of the alkaloids from the genus Equisetum

INTRODUCTION

The plant family Equisetaceae (Equisetopsida, Monilophyta; common name: horsetails) is part of an ancient group of spore producing plants. Today, Equisetum is the only surviving genus comprising 15 species in two subgenera (Equisetum and Hippochaete). Several unique alkaloids are described to occur in this genus, so far there is very little data on the occurrence and the amount of those alkaloids for the different species.

OBJECTIVE

To establish an extraction method and an analytical method to detect and quantify the relevant Equisetum-type alkaloids and to create a quantitative data set on the alkaloid content of all Equisetum species worldwide.

METHODOLOGY

Hydrophilic interaction liquid chromatography high-performance liquid chromatography tandem mass spectrometry (HILIC HPLC-MS/MS) in electrospray ionisation (ESI) positive mode was used to analyse and quantify the alkaloid content of 68 Equisetum samples.

RESULTS

The presence of nicotine in at least one sample of each Equisetum species could be demonstrated. The total nicotine amount rarely exceeded 250 μg/kg and 50 μg/kg for the subgenus Equisetum and Hippochaete, respectively. Besides nicotine, Equisetum-type alkaloids (mainly palustrine and palustridiene) were only detected in three species, namely E. palustre, E. bogotense and E. giganteum. For E. giganteum, palustridiene was detected at levels around the limit od detection (LoD) (25 μg/kg), whereas in E. palustre and E. bogotense, both alkaloids (palustrine and palustridiene) were detected at much higher levels (20-800 mg/kg).

CONCLUSIONS

All Equisetum species occurring worldwide were successfully subjected to a detailed qualitative and quantitative alkaloid analysis using a newly developed HILIC-HPLC-ESIpos-MS/MS approach. The data set can be used to distinguish different Equisetum-chemotypes.

Potential of Equisetum ramosissimum Desf. for remediation of antimony flotation tailings: a case study

A flooding event caused collapsing of the Stolice flotation tailing dam and spilling of large volumes of sludge into environment. Urgent remediation measures have not been applied due to the lack of financial resources. Remediation values for Sb, Zn, and Pb in the flotation tailing samples were exceeded 20.5, 4.2, and 1.15 times, respectively, emphasizing the need for remediation. Plants growing on mine spoils represent useful tools for environmental monitoring and soil remediation. The appearance of Equisetum ramosissimum as a dominant colonizer on the flotation tailings indicates that biological reclamation of the site is possible. Equisetum ramosissimum shows the ability to phytostabilize and immobilize available fractions of Fe, Mn, Zn, Pb, and Sb. Transfer rate of metals from roots to shoots reveals exclusion of elements from the shoots, preventing their further spreading through the food chain. The results of this study show that E. ramosissimum can be an additional tool for environmental monitoring and remediation of flotation tailings after hazardous events.

Origin of Equisetum: Evolution of horsetails (Equisetales) within the major euphyllophyte clade Sphenopsida

PREMISE OF THE STUDY

Equisetum is the sole living representative of Sphenopsida, a clade with impressive species richness, a long fossil history dating back to the Devonian, and obscure relationships with other living pteridophytes. Based on molecular data, the crown group age of Equisetum is mid-Paleogene, although fossils with possible crown synapomorphies appear in the Triassic. The most widely circulated hypothesis states that the lineage of Equisetum derives from calamitaceans, but no comprehensive phylogenetic studies support the claim. Using a combined approach, we provide a comprehensive phylogenetic analysis of Equisetales, with special emphasis on the origin of genus Equisetum.

METHODS

We performed parsimony phylogenetic analyses to address relationships of 43 equisetalean species (15 extant, 28 extinct) using a combination of morphological and molecular characters.

KEY RESULTS

We recovered Equisetaceae + Neocalamites as sister to Calamitaceae + a clade of Angaran and Gondwanan horsetails, with the four groups forming a clade that is sister to Archaeocalamitaceae. The estimated age for the Equisetum crown group is mid-Mesozoic.

CONCLUSIONS

Modern horsetails are not nested within calamitaceans; instead, both groups have explored independent evolutionary trajectories since the Carboniferous. Diverse fossil taxon sampling helps to shed light on the position and relationships of equisetalean lineages, of which only a tiny remnant is present within the extant flora. Understanding these relationships and early character configurations of ancient plant clades as Equisetales provide useful tests of hypotheses about overall phylogenetic relationships of euphyllophytes and foundations for future tests of molecular dates with paleontological data.

The remarkable stomata of horsetails (Equisetum): patterning, ultrastructure and development

BACKGROUND AND AIMS

The stomata of Equisetum - the sole extant representative of an ancient group of land plants - are unique with respect to both structure and development, yet little is known about details of ultrastructure and patterning, and existing accounts of key developmental stages are conflicting.

METHODS

We used light and electron microscopy to examine mature stomata and stomatal development in Equisetum myriochaetum, and compared them with other land plants, including another putative fern relative, Psilotum We reviewed published reports of stomatal development to provide a comprehensive discussion of stomata in more distantly related taxa.

KEY RESULTS

Stomatal development in Equisetum is basipetal and sequential in strict linear cell files, in contrast with Psilotum, in which stomatal development occurs acropetally. In Equisetum, cell asymmetry occurs in the axial stomatal cell file, resulting in a meristemoidal mother cell that subsequently undergoes two successive asymmetric mitoses. Each stomatal cell complex is formed from a single precursor meristemoid, and consists of four cells: two guard cells and two mesogene subsidiary cells. Late periclinal divisions occur in the developing intervening cells.

CONCLUSIONS

In addition to the unique mature structure, several highly unusual developmental features include a well-defined series of asymmetric and symmetric mitoses in Equisetum, which differs markedly from Psilotum and other land plants. The results contribute to our understanding of the diverse patterns of stomatal development in land plants, including contrasting pathways to paracytic stomata. They add to a considerable catalogue of highly unusual traits of horsetails - one of the most evolutionarily isolated land-plant taxa.

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.

Cytological and proteomic analyses of horsetail (Equisetum arvense L.) spore germination

Spermatophyte pollen tubes and root hairs have been used as single-cell-type model systems to understand the molecular processes underlying polar growth of plant cells. Horsetail (Equisetum arvense L.) is a perennial herb species in Equisetopsida, which creates separately growing spring and summer stems in its life cycle. The mature chlorophyllous spores produced from spring stems can germinate without dormancy. Here we report the cellular features and protein expression patterns in five stages of horsetail spore germination (mature spores, rehydrated spores, double-celled spores, germinated spores, and spores with protonemal cells). Using 2-DE combined with mass spectrometry, 80 proteins were found to be abundance changed upon spore germination. Among them, proteins involved in photosynthesis, protein turnover, and energy supply were over-represented. Thirteen proteins appeared as proteoforms on the gels, indicating the potential importance of post-translational modification. In addition, the dynamic changes of ascorbate peroxidase, peroxiredoxin, and dehydroascorbate reductase implied that reactive oxygen species homeostasis is critical in regulating cell division and tip-growth. The time course of germination and diverse expression patterns of proteins in photosynthesis, energy supply, lipid and amino acid metabolism indicated that heterotrophic and autotrophic metabolism were necessary in light-dependent germination of the spores. Twenty-six proteins were involved in protein synthesis, folding, and degradation, indicating that protein turnover is vital to spore germination and rhizoid tip-growth. Furthermore, the altered abundance of 14-3-3 protein, small G protein Ran, actin, and caffeoyl-CoA O-methyltransferase revealed that signaling transduction, vesicle trafficking, cytoskeleton dynamics, and cell wall modulation were critical to cell division and polar growth. These findings lay a foundation toward understanding the molecular mechanisms underlying fern spore asymmetric division and rhizoid polar growth.

Genome size expansion and the relationship between nuclear DNA content and spore size in the Asplenium monanthes fern complex (Aspleniaceae)

BACKGROUND

Homosporous ferns are distinctive amongst the land plant lineages for their high chromosome numbers and enigmatic genomes. Genome size measurements are an under exploited tool in homosporous ferns and show great potential to provide an overview of the mechanisms that define genome evolution in these ferns. The aim of this study is to investigate the evolution of genome size and the relationship between genome size and spore size within the apomictic Asplenium monanthes fern complex and related lineages.

RESULTS

Comparative analyses to test for a relationship between spore size and genome size show that they are not correlated. The data do however provide evidence for marked genome size variation between species in this group. These results indicate that Asplenium monanthes has undergone a two-fold expansion in genome size.

CONCLUSIONS

Our findings challenge the widely held assumption that spore size can be used to infer ploidy levels within apomictic fern complexes. We argue that the observed genome size variation is likely to have arisen via increases in both chromosome number due to polyploidy and chromosome size due to amplification of repetitive DNA (e.g. transposable elements, especially retrotransposons). However, to date the latter has not been considered to be an important process of genome evolution within homosporous ferns. We infer that genome evolution, at least in some homosporous fern lineages, is a more dynamic process than existing studies would suggest.

DNA barcoding the Canadian Arctic flora: core plastid barcodes (rbcL + matK) for 490 vascular plant species

Accurate identification of Arctic plant species is critical for understanding potential climate-induced changes in their diversity and distributions. To facilitate rapid identification we generated DNA barcodes for the core plastid barcode loci (rbcL and matK) for 490 vascular plant species, representing nearly half of the Canadian Arctic flora and 93% of the flora of the Canadian Arctic Archipelago. Sequence recovery was higher for rbcL than matK (93% and 81%), and rbcL was easier to recover than matK from herbarium specimens (92% and 77%). Distance-based and sequence-similarity analyses of combined rbcL + matK data discriminate 97% of genera, 56% of species, and 7% of infraspecific taxa. There is a significant negative correlation between the number of species sampled per genus and the percent species resolution per genus. We characterize barcode variation in detail in the ten largest genera sampled (Carex, Draba, Festuca, Pedicularis, Poa, Potentilla, Puccinellia, Ranunculus, Salix, and Saxifraga) in the context of their phylogenetic relationships and taxonomy. Discrimination with the core barcode loci in these genera ranges from 0% in Salix to 85% in Carex. Haplotype variation in multiple genera does not correspond to species boundaries, including Taraxacum, in which the distribution of plastid haplotypes among Arctic species is consistent with plastid variation documented in non-Arctic species. Introgression of Poa glauca plastid DNA into multiple individuals of P. hartzii is problematic for identification of these species with DNA barcodes. Of three supplementary barcode loci (psbA-trnH, psbK-psbI, atpF-atpH) collected for a subset of Poa and Puccinellia species, only atpF-atpH improved discrimination in Puccinellia, compared with rbcL and matK. Variation in matK in Vaccinium uliginosum and rbcL in Saxifraga oppositifolia corresponds to variation in other loci used to characterize the phylogeographic histories of these Arctic-alpine species.

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.

Evolution of mixed-linkage (1 -> 3, 1 -> 4)-β-D-glucan (MLG) and xyloglucan in Equisetum (horsetails) and other monilophytes

BACKGROUND AND AIMS

Horsetails (Equisetopsida) diverged from other extant eusporangiate monilophytes in the Upper Palaeozoic. They are the only monilophytes known to contain the hemicellulose mixed-linkage (1 → 3, 1 → 4)-β-d-glucan (MLG), whereas all land plants possess xyloglucan. It has been reported that changes in cell-wall chemistry often accompanied major evolutionary steps. We explored changes in hemicelluloses occurring during Equisetum evolution.

METHODS

Hemicellulose from numerous monilophytes was treated with lichenase and xyloglucan endoglucanase. Lichenase digests MLG to di-, tri- and tetrasaccharide repeat-units, resolvable by thin-layer chromatography.

KEY RESULTS

Among monilophytes, MLG was confined to horsetails. Our analyses support a basal trichotomy of extant horsetails: MLG was more abundant in subgenus Equisetum than in subgenus Hippochaete, and uniquely the sister group E. bogotense yielded almost solely the tetrasaccharide repeat-unit (G4G4G3G). Other species also gave the disaccharide, whereas the trisaccharide was consistently very scarce. Tetrasaccharide : disaccharide ratios varied interspecifically, but with no consistent difference between subgenera. Xyloglucan was scarce in Psilotum and subgenus Equisetum, but abundant in subgenus Hippochaete and in the eusporangiate ferns Marattia and Angiopteris; leptosporangiate ferns varied widely. All monilophytes shared a core pattern of xyloglucan repeat-units, major XEG products co-chromatographing on thin-layer chromatography with non-fucosylated hepta-, octa- and nonasaccharides and fucose-containing nona- and decasaccharides.

CONCLUSIONS

G4G4G3G is the ancestral repeat-unit of horsetail MLG. Horsetail evolution was accompanied by quantitative and qualitative modification of MLG; variation within subgenus Hippochaete suggests that the structure and biosynthesis of MLG is evolutionarily plastic. Xyloglucan quantity correlates negatively with abundance of other hemicelluloses; but qualitatively, all monilophyte xyloglucans conform to a core pattern of repeat-unit sizes.

An extensin-rich matrix lines the carinal canals in Equisetum ramosissimum, which may function as water-conducting channels

BACKGROUND AND AIMS

The anatomy of Equisetum stems is characterized by the occurrence of vallecular and carinal canals. Previous studies on the carinal canals in several Equisetum species suggest that they convey water from one node to another.

METHODS

Cell wall composition and ultrastructure have been studied using immunocytochemistry and electron microscopy, respectively. Serial sectioning and X-ray computed tomography were employed to examine the internode-node-internode transition of Equisetum ramosissimum.

KEY RESULTS

The distribution of the LM1 and JIM20 extensin epitopes is restricted to the lining of carinal canals. The monoclonal antibodies JIM5 and LM19 directed against homogalacturonan with a low degree of methyl esterification and the CBM3a probe recognizing crystalline cellulose also bound to this lining. The xyloglucan epitopes recognized by LM15 and CCRC-M1 were only detected in this lining after pectate lyase treatment. The carinal canals, connecting consecutive rings of nodal xylem, are formed by the disruption and dissolution of protoxylem elements during elongation of the internodes. Their inner surface appears smooth compared with that of vallecular canals.

CONCLUSIONS

The carinal canals in E. ramosissimum have a distinctive lining containing pectic homogalacturonan, cellulose, xyloglucan and extensin. These canals might function as water-conducting channels which would be especially important during the elongation of the internodes when protoxylem is disrupted and the metaxylem is not yet differentiated. How the molecularly distinct lining relates to the proposed water-conducting function of the carinal canals requires further study. Efforts to elucidate the spatial and temporal distribution of cell wall polymers in a taxonomically broad range of plants will probably provide more insight into the structural-functional relationships of individual cell wall components or of specific configurations of cell wall polymers.

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.

Equisetum species show uniform epicuticular wax structures but diverse composition patterns

BACKGROUND AND AIMS

Only few data on the epicuticular waxes (EWs) of horsetails are available. This contribution therefore focuses on the wax micromorphology and chemical composition of Equisetum species of the subgenera Equisetum and Hippochaete.

METHODOLOGY

Distribution patterns and structural details of EW on the shoots were studied by scanning electron microscopy. After extraction with chloroform, the chemical composition of wax isolates was analysed by gas chromatography.

PRINCIPAL RESULTS

Epicuticular wax crystals were non-oriented platelets or membraneous platelets. They were usually located on subsidiary cells of stomata and adjacent cells. Other parts of the shoots were covered mainly with a smooth wax film or small granules only. The chemical constituents found were alkanes, esters, aldehydes, primary alcohols and free fatty acids in a range of C(20)-C(36) (in esters C(36)-C(56)). All species of the subgenus Hippochaete showed a similar pattern of fractions with high percentages of alkanes and aldehydes, whereas the subgenus Equisetum species had distinctly different wax compositions. Extracts from the internodes-surfaces without well-developed EW crystals and only few stomata-showed the lowest contents of aldehydes.

CONCLUSIONS

The covering with EW crystals will provide unhindered gas exchange and, combined with intracuticular wax, may prevent excess water loss during winter in the evergreen shoots of the subgenus Hippochaete. The results indicate that the Equisetum wax micromorphology and biosynthesis are comparable to EW of other pteridophyte classes and mosses.

Utility of a large, multigene plastid data set in inferring higher-order relationships in ferns and relatives (monilophytes)

PREMISE OF THE STUDY

The monilophytes (ferns and relatives)-the third largest group of land plants-exhibit a diverse array of vegetative and reproductive morphologies. Investigations into their early ecological and life-history diversification require accurate, well-corroborated phylogenetic estimates. We examined the utility of a large plastid-based data set in inferring backbone relationships for monilophytes. •

METHODS

We recovered 17 plastid genes for exemplar taxa using published and new primers. We compared results from maximum-likelihood and parsimony analyses, assessed the effects of removing rapidly evolving characters, and examined the extent to which our data corroborate or contradict the results of other studies, or resolve current ambiguities. •

KEY RESULTS

Considering multifamily clades, we found bootstrap support comparable to or better than that in published studies that used fewer genes from fewer or more taxa. We firmly establish filmy ferns (Hymenophyllales) as the sister group of all leptosporangiates except Osmundaceae, resolving the second deepest split in leptosporangiate-fern phylogeny. A clade comprising Ophioglossaceae and Psilotaceae is currently accepted as the sister group of other monilophytes, but we recover Equisetum in this position. We also recover marattioid and leptosporangiate ferns as sister groups. Maximum-likelihood rate-class estimates are somewhat skewed when a long-branch lineage (Selaginella) is included, negatively affecting bootstrap support for early branches. •

CONCLUSIONS

Our findings support the utility of this gene set in corroborating relationships found in previous studies, improving support, and resolving uncertainties in monilophyte phylogeny. Despite these advances, our results also underline the need for continued work on resolving the very earliest splits in monilophyte phylogeny.

Phylogenetic diversification of Equisetum (Equisetales) as inferred from Lower Cretaceous species of British Columbia, Canada

Three types of anatomically preserved vegetative shoots with features that characterize crown group Equisetum have been discovered in Lower Cretaceous deposits (≈136 Ma) of British Columbia, Canada, suggesting the genus is much older than currently believed. Specimens include two types of aerial shoots described as E. haukeanum sp. nov. and E. vancouverense sp. nov. and one type of subterranean rhizome. Shoots are 1-2 mm in diameter, jointed, and in cross section have fluted stems with a hollow pith. Distinctive patterns of cortical sclerenchyma and different ridge morphologies characterize each shoot morphotype. Nodes display irregular branching, highly fused leaf sheaths, and a nodal diaphragm. The aerial stem morphospecies have vallecular canals on alternating radii with carinal canals of an equisetostele surrounded by only a few tracheids. No secondary tissues are produced. Bands of surficial stomata flank the furrows of one morphospecies. Rhizomes and aerial shoots are of a similar size, suggesting that the plants were equivalent in stature to the smallest living Equisetum species. These fossils augment our understanding of evolutionary transformations that led from Paleozoic Archaeocalamitaceae and Calamitaceae to crown group Equisetaceae, suggesting that the initial diversification of Equisetum began far earlier than suggested by molecular-clock-based estimates.

Development and ecological implications of dormant buds in the high-Paleolaltitude Triassic sphenophyte Spaciinodum (Equisetaceae)

Spaciinodum collinsonii, a Triassic sphenophyte from the central Transantarctic Mountains, Antarctica, is reinterpreted based on new material in order to clarify discrepancies from previous work and to detail the development and ecology of the Spaciinodum plant. Vegetative stems have alternating nodes and internodes, nodes distinguished by a solid diaphragm of tissue, internodes by the presence of vallecular (cortical) and carinal canals, and a hollow pith. Whorls of branches arise immediately above the nodes, alternating with the leaves of the subjacent nodes. Branches develop in the cortex and are anatomically similar to the stems. While Spaciinodum is similar to extant Equisetum, it is distinctive in that its large vallecular canals form a complete ring within the cortex and are separated only by thin fimbrils of tissue. The majority of specimens of Spaciinodum are now believed to be dormant buds with condensed nodes and internodes, with progressively longer internodal regions more basally. More apical portions of buds have cellular internodes because the areas where the canals will form have not yet ruptured from elongation. The abundance of buds and the absence of elongated stems in the permineralized peat deposit suggest that Spaciinodum underwent dormancy during the dark Antarctic winters.

Mixed-linkage (1-->3),(1-->4)-beta-D-glucan is not unique to the Poales and is an abundant component of Equisetum arvense cell walls

Mixed-linkage (1-->3),(1-->4)-beta-D-glucan (MLG) is widely considered to be a defining feature of the cell walls of plants in the Poales order. However, we conducted an extensive survey of cell-wall composition in diverse land plants and discovered that MLG is also abundant in the walls of the horsetail Equisetum arvense. MALDI-TOF MS and monosaccharide linkage analysis revealed that MLG in E. arvense is an unbranched homopolymer that consists of short blocks of contiguous 1,4-beta-linked glucose residues joined by 1,3-beta linkages. However, in contrast to Poaceae species, MLG in E. arvense consists mostly of cellotetraose rather than cellotetriose, and lacks long 1,4-beta-linked glucan blocks. Monosaccharide linkage analyses and immunochemical profiling indicated that, in E. arvense, MLG is a component of cell walls that have a novel architecture that differs significantly from that of the generally recognized type I and II cell walls. Unlike in type II walls, MLG in E. arvense does not appear to be co-extensive with glucuroarabinoxylans but occurs in walls that are rich in pectin. Immunofluorescence and immunogold localization showed that MLG occurs in both young and old regions of E. arvense stems, and is present in most cell types apart from cells in the vascular tissues. These findings have important implications for our understanding of cell-wall evolution, and also demonstrate that plant cell walls can be constructed in a way not previously envisaged.