Polypod Ferns Research Articles

Geographic patterns and climatic drivers of phylogenetic structure of liverworts along a long elevational gradient in the central Himalaya

AbstractFor clades originating in warm climates, the tropical niche conservatism hypothesis predicts that current biological assemblages in colder or drier climates are expected to have lower phylogenetic diversity, and species in colder or drier climates are expected to be more closely related to each other (i.e., higher phylogenetic clustering). Liverworts are one of the oldest clades of extant land plants. They originated about 500 Ma during a warm (“greenhouse”) period and experienced multiple major cycles of warm and cold periods. Here, I test the tropical niche conservatism hypothesis using liverwort assemblages distributed along an elevational gradient crossing about 5000 m of elevation in the central Himalaya. I found that, in general, phylogenetic diversity and dispersion decrease with increasing elevation and thus with decreasing temperature, which is consistent with the tropical niche conservatism hypothesis. Phylogenetic diversity decreases with elevation monotonically, but phylogenetic dispersion decreases with elevation in a triphasic (zig‐zag) pattern, which is generally consistent with the triphasic pattern found in angiosperms and polypod ferns along the same elevational gradient. Temperature‐related variables explained approximately the same amount of the variation in phylogenetic diversity and dispersion as did precipitation‐related variables, although mean annual temperature explained 9%−15% more variation than did annual precipitation. Climate extreme variables explained approximately the same amount of variation in phylogenetic diversity and dispersion as did climate seasonality variables.

Revision of the Barremian fern Coniopteris laciniata from Las Hoyas and El Montsec (Spain): Highlighting its importance in the evolution of vegetation during the Early Cretaceous

AbstractThe species Coniopteris laciniata and Sphenopteris wonnacottii are heterophyllous ferns recovered from two Spanish Barremian localities, Las Hoyas and El Montsec respectively. The similarities between these species, observed in a study of a total of 66 hand specimens from both localities, indicate that they are conspecific. Following the rule of priority in botanical nomenclature, and because there are doubts about the assignment of this species to a higher taxonomic rank, the name Coniopteris is maintained. Characters of this fern and additional characters of other species of Coniopteris would support a diversification of polypod ferns during the Early Cretaceous. Metric architecture analyses suggest that the heterophylly of the plant was probably caused by the submersion of the apical part of fronds in water during their development, which would be consistent with the taphonomy of the remains in both localities.

Microlepia burmasia sp. nov., a new fern species from mid-Cretaceous Kachin amber of norther Myanmar (Dennstaedtiaceae, Polypodiales)

The rise of angiosperms during the Cretaceous was thought to be related to the radiation of polypod ferns, a fern lineage that represent 80% of the modern fern diversity. However, although the proposed palo-diversity from DNA based studies, Mesozoic polypod fern fossils with preserved fertile pinnae are scarcely. Here, we investigated the fragment of polypod fern preserved in mid-Cretaceous Kachin amber from northern Myanmar and assigned a new fossilized fertile pinnule into the genus Microlepia (Dennstaedtiaceae), described as Microlepia burmasia Long, Wang and Shi, sp. nov. The new species is mainly characterized by the 2-pinnate-pinnatifid pinnule with surface and margin covering short tomentum and articulate hairs. Vein free, pouch-shaped indusia, submarginal and terminal on one vein of sori, sporangium with interrupted, vertical annulus and spores trilete. This discovery adds to polypod fern diversity in the Cretaceous and dates the origin of Microlepia to at least 60 million years earlier, which is evidence for an early origin of polypod ferns and coincides with the rise of angiosperms.

Abundance and seasonal growth of epiphytic ferns at three sites along a rainfall gradient in Western Europe

Vascular epiphytes in temperate zones are allegedly rare due to climatic constraints, such as drought and freezing temperatures during winter. Here, we investigate how abundance and seasonal growth of epiphytic polypod ferns in Western Europe are influenced by annual rainfall and temperature. We recorded abundances and growth of epiphytic polypod ferns over two years at three sites along a rainfall gradient from Southwest Ireland to Northwest Germany, spanning a two-fold difference in annual rainfall. We also investigated plant maturation and recorded key climate characteristics (rainfall and temperature). Abundance of epiphytic polypod ferns strongly decreased from the wetter end of the rainfall gradient in Ireland towards the drier end in Germany. Yet, frond turnover was equally high at all study sites during summer months, and equally low during winter. Plants showed only little to no expansive growth during the study period, except for the study site in France in the middle of the gradient, where the total number of fronds strongly increased. Similarly, we found an increase in the proportion of spore-bearing fronds at the French study site, whereas there was hardly any change between years at the other two sites. The observed growth patterns are inconsistent with the current differences in abundance of epiphytic ferns. We suggest that these differences are due to poor germination of spores under drier conditions and that small differences in annual growth have contributed to the current abundances over an extended time period. Surprisingly, seasonal frond productivity appeared to be unaffected by the amount of annual rainfall and average temperatures, although it seems likely that these factors do play a role during gametophyte establishment.

The Expansion and Diversification of Pentatricopeptide Repeat RNA-Editing Factors in Plants

The RNA-binding pentatricopeptide repeat (PPR) family comprises hundreds to thousands of genes in most plants, but only a few dozen in algae, indicating massive gene expansions during land plant evolution. The nature and timing of these expansions has not been well defined due to the sparse sequence data available from early-diverging land plant lineages. In this study, we exploit the comprehensive OneKP datasets of over 1000 transcriptomes from diverse plants and algae toward establishing a clear picture of the evolution of this massive gene family, focusing on the proteins typically associated with RNA editing, which show the most spectacular variation in numbers and domain composition across the plant kingdom. We characterize over 2 250 000 PPR motifs in over 400 000 proteins. In lycophytes, polypod ferns, and hornworts, nearly 10% of expressed protein-coding genes encode putative PPR editing factors, whereas they are absent from algae and complex-thalloid liverworts. We show that rather than a single expansion, most land plant lineages with high numbers of editing factors have continued to generate novel sequence diversity. We identify sequence variations that imply functional differences between PPR proteins in seed plants versus non-seed plants and variations we propose to be linked to seed-plant-specific editing co-factors. Finally, using the sequence variations across the datasets, we develop a structural model of the catalytic DYW domain associated with C-to-U editing and identify a clade of unique DYW variants that are strong candidates as U-to-C RNA-editing factors, given their phylogenetic distribution and sequence characteristics.

Comparative analysis of inverted repeats of polypod fern (Polypodiales) plastomes reveals two hypervariable regions

BackgroundFerns are large and underexplored group of vascular plants (~ 11 thousands species). The genomic data available by now include low coverage nuclear genomes sequences and partial sequences of mitochondrial genomes for six species and several plastid genomes.ResultsWe characterized plastid genomes of three species of Dryopteris, which is one of the largest fern genera, using sequencing of chloroplast DNA enriched samples and performed comparative analysis with available plastomes of Polypodiales, the most species-rich group of ferns. We also sequenced the plastome of Adianthum hispidulum (Pteridaceae). Unexpectedly, we found high variability in the IR region, including duplication of rrn16 in D. blanfordii, complete loss of trnI-GAU in D. filix-mas, its pseudogenization due to the loss of an exon in D. blanfordii. Analysis of previously reported plastomes of Polypodiales demonstrated that Woodwardia unigemmata and Lepisorus clathratus have unusual insertions in the IR region. The sequence of these inserted regions has high similarity to several LSC fragments of ferns outside of Polypodiales and to spacer between tRNA-CGA and tRNA-TTT genes of mitochondrial genome of Asplenium nidus. We suggest that this reflects the ancient DNA transfer from mitochondrial to plastid genome occurred in a common ancestor of ferns. We determined the marked conservation of gene content and relative evolution rate of genes and intergenic spacers in the IRs of Polypodiales. Faster evolution of the four intergenic regions had been demonstrated (trnA- orf42, rrn16-rps12, rps7-psbA and ycf2-trnN).ConclusionsIRs of Polypodiales plastomes are dynamic, driven by such events as gene loss, duplication and putative lateral transfer from mitochondria.

A fossil species of the enigmatic early polypod fern genus Cystodium (Cystodiaceae) in Cretaceous amber from Myanmar

The monospecific fern genus Cystodium (Cystodiaceae; Polypodiales) occurs exclusively in the tropical forests of the Malay Archipelago, the Admiralty Islands, the Louisiade Archipelago, and the Solomon Islands. Divergence time estimates suggest that the genus originated in the Mesozoic; however, fossil evidence to validate this suggestion has been lacking. Amber from Myanmar (Burmese amber) is an important source of new information on the diversity of vascular cryptogams in the Cretaceous. This paper describes the fossil taxon Cystodium sorbifolioides nov. sp. based on a fragment of a fertile leaf preserved in Burmese amber that represents the first fossil evidence of the family Cystodiaceae. Cystodium sorbifolioides is used to obtain a minimum age estimate for the Cystodiaceae and the closely related, monogeneric Lonchitidaceae and Lindsaeaceae. The fossil strengthens the hypothesis that the forest ecosystems of Malesia and Melanesia represent refugia for many tropical plant lineages that originated in the Cretaceous.

The first fossil of Lindsaeaceae (Polypodiales) from the Cretaceous amber forest of Myanmar

Burmese amber is currently the most important source of Cretaceous amber-preserved plants. Recent findings indicate a rich cryptogamic diversity in the source forests of this amber. Besides of liverworts and mosses, several fossils of polypod ferns have been discovered, so far. Here, we report a new fern inclusion from Burmese amber which represents the first leaf fossil of the polypod family Lindsaeaceae. The fossil shows all characteristics of extant Lindsaeaceae, however, it remains unclear if it belongs to an extant or an extinct genus. Along with the sole other Cretaceous Lindsaeaceae fossil, a root fossil from the Albian of North America, the new fossil indicates a wide distribution of this fern family in the Northern Hemisphere during the late Early Cretaceous.

Phylogenetic Relationships of the Fern Cyrtomium falcatum (Dryopteridaceae) from Dokdo Island Based on Chloroplast Genome Sequencing.

Cyrtomium falcatum is a popular ornamental fern cultivated worldwide. Native to the Korean Peninsula, Japan, and Dokdo Island in the Sea of Japan, it is the only fern present on Dokdo Island. We isolated and characterized the chloroplast (cp) genome of C. falcatum, and compared it with those of closely related species. The genes trnV-GAC and trnV-GAU were found to be present within the cp genome of C. falcatum, whereas trnP-GGG and rpl21 were lacking. Moreover, cp genomes of Cyrtomium devexiscapulae and Adiantum capillus-veneris lack trnP-GGG and rpl21, suggesting these are not conserved among angiosperm cp genomes. The deletion of trnR-UCG, trnR-CCG, and trnSeC in the cp genomes of C. falcatum and other eupolypod ferns indicates these genes are restricted to tree ferns, non-core leptosporangiates, and basal ferns. The C. falcatum cp genome also encoded ndhF and rps7, with GUG start codons that were only conserved in polypod ferns, and it shares two significant inversions with other ferns, including a minor inversion of the trnD-GUC region and an approximate 3 kb inversion of the trnG-trnT region. Phylogenetic analyses showed that Equisetum was found to be a sister clade to Psilotales-Ophioglossales with a 100% bootstrap (BS) value. The sister relationship between Pteridaceae and eupolypods was also strongly supported by a 100% BS, but Bayesian molecular clock analyses suggested that C. falcatum diversified in the mid-Paleogene period (45.15 ± 4.93 million years ago) and might have moved from Eurasia to Dokdo Island.

Applying DNA Barcodes to Identify Closely Related Species of Ferns: A Case Study of the Chinese Adiantum (Pteridaceae)

DNA barcoding is a fast-developing technique to identify species by using short and standard DNA sequences. Universal selection of DNA barcodes in ferns remains unresolved. In this study, five plastid regions (rbcL, matK, trnH-psbA, trnL-F and rps4-trnS) and eight nuclear regions (ITS, pgiC, gapC, LEAFY, ITS2, IBR3_2, DET1, and SQD1_1) were screened and evaluated in the fern genus Adiantum from China and neighboring areas. Due to low primer universality (matK) and/or the existence of multiple copies (ITS), the commonly used barcodes matK and ITS were not appropriate for Adiantum. The PCR amplification rate was extremely low in all nuclear genes except for IBR3_2. rbcL had the highest PCR amplification rate (94.33%) and sequencing success rate (90.78%), while trnH-psbA had the highest species identification rate (75%). With the consideration of discriminatory power, cost-efficiency and effort, the two-barcode combination of rbcL+ trnH-psbA seems to be the best choice for barcoding Adiantum, and perhaps basal polypod ferns in general. The nuclear IBR3_2 showed 100% PCR amplification success rate in Adiantum, however, it seemed that only diploid species could acquire clean sequences without cloning. With cloning, IBR3_2 can successfully distinguish cryptic species and hybrid species from their related species. Because hybridization and allopolyploidy are common in ferns, we argue for including a selected group of nuclear loci as barcodes, especially via the next-generation sequencing, as it is much more efficient to obtain single-copy nuclear loci without the cloning procedure.

Sequence stratigraphy and environmental background of the late Pleistocene and Holocene occupation in the Southeast Primor'ye (the Russian Far East)

The paper presents the results of Quaternary palaeoecology and geoarchaeology studies in the Zerkal'naya Basin, with new insights about sequenced natural shifts during the prehistoric occupation of this marginally explored NE Asian maritime territory. The Basin is part of the continental drainage system and the main physiographic and biotic corridor for peopling of the transitive coastal interior SE Primor'ye Region. The Final Pleistocene and Holocene environmental (biotic and abiotic) proxy records from the Upper/Final Palaeolithic to early historical sites document a dynamic climate change with vegetation cover transformations within riverine and mountain valley ecosystems of the Russian Far East. Most of the archaeological sites located on the low terraces and bedrock promontories along the main river channel and its tributary streams suggest traditional hunter gathered lifestyles based on seasonal salmon-fishing supplemented by pastoral economy.Tundra-forests with larch trees, dwarf birch thickets and polypod ferns from the basal stratigraphic units of the late Last Glacial occupation sites associated with the Upper Palaeolithic micro-blade and bifacial stone tool traditions (14C-dated to 19,000–12,000 cal yrs BP) indicate rather pronounced conditions and much lower MAT comparing today. Following a final Pleistocene cooling event, a major climate warming marked the onset of Holocene accompanied by a regional humidity increase promoting the formation of a mixed broadleaved-coniferous oak-dominant taiga, and culminating in the mid-Holocene Climatic Optimum. The appearance of mosaic parklands ca. 5,000–4,000 cal yrs BP. may be partly attributed to the expansion of the Far Eastern Neolithic cultures practicing forest clearance for pastures and dwellings. A progressing landscape opening indicated by the spread of light-demanding thickets and birch-dominated riverine biotopes with Artemisia suggests a further vegetation cover transformation during the late Neolithic and the early Palaeo-Metal (Bronze Age) periods. This trend corroborates the documented climate deterioration between 3,400 and 2,600 cal yrs BP, causing a regional aridification with a parkland-steppe broadening in the main SE Primor'ye river valleys. The late Holocene climate development persisted until the Little Ice Age which led to formation of the present settlement ecosystems with mixed (oak/cedar/fir-dominated) temperate maritime woodlands.

Burmese amber fossils bridge the gap in the Cretaceous record of polypod ferns

Cretaceous fossils of derived leptosporangiate ferns (Polypodiales) are exceedingly rare yet they are needed to confirm the hypothesis of a Cretaceous diversification of polypod ferns as predicted by DNA-based divergence time estimates. Here we show that diverse polypod ferns existed in the mid-Cretaceous woodlands of Myanmar. We describe isolated sporangia with a vertical, broken annulus ring containing a differentiated stomium as well as distinguished pinnae fragments. Krameropteris resinatus gen. et sp. nov. is described based on a pinnae-fragment with free branched veins, exindusiate sori and polypod sporangia with trilete spores, and assigned to the early diverging polypod fern lineage Dennstaedtiaceae. Integration of the new fossil evidence in a phylogenetic framework provides support to the hypothesis of a Cretaceous diversification of polypod ferns.

Sporangium Exposure and Spore Release in the Peruvian Maidenhair Fern (Adiantum peruvianum, Pteridaceae).

We investigated the different processes involved in spore liberation in the polypod fern Adiantum peruvianum (Pteridaceae). Sporangia are being produced on the undersides of so-called false indusia, which are situated at the abaxial surface of the pinnule margins, and become exposed by a desiccation-induced movement of these pinnule flaps. The complex folding kinematics and functional morphology of false indusia are being described, and we discuss scenarios of movement initiation and passive hydraulic actuation of these structures. High-speed cinematography allowed for analyses of fast sporangium motion and for tracking ejected spores. Separation and liberation of spores from the sporangia are induced by relaxation of the annulus (the ‘throwing arm’ of the sporangium catapult) and conservation of momentum generated during this process, which leads to sporangium bouncing. The ultra-lightweight spores travel through air with a maximum velocity of ~5 m s-1, and a launch acceleration of ~6300g is measured. In some cases, the whole sporangium, or parts of it, together with contained spores break away from the false indusium and are shed as a whole. Also, spores can stick together and form spore clumps. Both findings are discussed in the context of wind dispersal.

Chloroplast phylogenomics resolves key relationships in ferns

AbstractStudies on chloroplast genomes of ferns and lycophytes are relatively few in comparison with those on seed plants. Although a basic phylogenetic framework of extant ferns is available, relationships among a few key nodes remain unresolved or poorly supported. The primary objective of this study is to explore the phylogenetic utility of large chloroplast gene data in resolving difficult deep nodes in ferns. We sequenced the chloroplast genomes from Cyrtomium devexiscapulae (Koidz.) Ching (eupolypod I) and Woodwardia unigemmata (Makino) Nakai (eupolypod II), and constructed the phylogeny of ferns based on both 48 genes and 64 genes. The trees based on 48 genes and 64 genes are identical in topology, differing only in support values for four nodes, three of which showed higher support values for the 48‐gene dataset. Equisetum L. was resolved as the sister to the Psilotales–Ophioglossales clade, and Equisetales–Psilotales–Ophioglossales clade was sister to the clade of the leptosporangiate and marattioid ferns. The sister relationship between the tree fern clade and polypods was supported by 82% and 100% bootstrap values in the 64‐gene and 48‐gene trees, respectively. Within polypod ferns, Pteridaceae was sister to the clade of Dennstaedtiaceae and eupolypods with a high support value, and the relationship of Dennstaedtiaceae–eupolypods was strongly supported. With recent parallel advances in the phylogenetics of ferns using nuclear data, chloroplast phylogenomics shows great potential in providing a framework for testing the impact of reticulate evolution in the early evolution of ferns.

Primary Hemiepiphytism inColysis ampla(Polypodiaceae) Provides New Insight into the Evolution of Growth Habit in Ferns

Premise of research. Epiphytes are prominent in many tropical floras; however, the evolution of epiphytism, especially among ferns, remains poorly understood. Transitions in habit have been proposed as evolutionary stepping stones in the radiation of ferns in the epiphytic niche, with hemiepiphytes playing an important role. However, few examples of hemiepiphytism have been conclusively documented in ferns, and evidence for this transition is limited. Because of this lack of information, the relationship between hemiepiphytism and epiphytism remains unclear. We fill this gap with new observations and analysis of habit evolution in the Polypodiaceae.Methodology. We document primary hemiepiphytism in Colysis ampla from field observations of both gametophytes and sporophytes, and we examine its sporophyte anatomy in relation to its growth habit. Using cpDNA sequence data, we place the species within a phylogenetic context and perform ancestral state reconstruction of growth habit to infer the evolution of hemiepiphytism in C. ampla.Pivotal results. Here we provide the first examination of gametophyte morphology and sporophyte growth habit in this species as well as the first conclusive documentation of primary hemiepiphytism in the Polypodiaceae. Phylogenetic analyses place C. ampla in a small clade of probable hemiepiphytes closely allied to the Old World ant-fern genus Lecanopteris. We infer a transition from epiphytism to hemiepiphytism in the clade consisting of C. ampla and closely related species, the first such transitional series reported for the polypod ferns. A hemiepiphyte syndrome consisting of gametophyte, rhizome, root, and leaf characteristics is presented to guide future investigation of this growth habit.Conclusions. Hemiepiphytes are likely underreported among climber- and epiphyte-rich groups of ferns. Primary hemiepiphytes may be more frequently derived from holoepiphytic ancestors because epiphytic gametophytes and sporophytes are preadapted to hemiepiphytic growth. We propose that hemiepiphytism provides a mechanism for acquisition of stable nutrient and water supplies by tree-dwelling plants.

Evaluation of angiosperm and fern contributions to soil organic matter using two methods of pyrolysis-gas chromatography-mass spectrometry

Ferns are an important plant group, and older phylogenies of non-polypod ferns contain relatively high concentrations of aliphatic leaf waxes, lignins, and tannins that could contribute to soil organic matter (SOM) biochemistry and stability. Pyrolysis gas-chromatography mass-spectrometry (py-GC/MS) analyzes biochemical fragments which can be related to lignin, polysaccharide, lipid, nitrogen (N)-bearing, non-lignin aromatics, and phenol source compounds. Thermochemolysis using tetramethylammonium hydroxide (TMAH) combined with py-GC/MS improves detection of lignin, cutin, and suberin-derived compounds. To examine the advantages and disadvantages of both methods for characterizing plant and soil biochemistry, we characterized non-polypod and polypod fern and angiosperm live tissues, roots and soils from the Kohala Mountains, Hawaii. Py-GC/MS provided a broad biochemical overview of compound groups including lignin, polysaccharide, lipid, N-bearing, non-lignin aromatics and phenol groups while TMAH-py-GC/MS detailed lignin units and fatty acids at the expense of the other categories. TMAH-py-GC/MS provided more detailed data on lignin, cutin, suberin and tannin-derived compounds. Both methods detected differences in lignin units between species, although p-coumaric and ferulic acids, predominantly found in ferns, were only observed with TMAH-py-GC/MS. Both py-GC/MS and TMAH-py-GC/MS are methods to detect compound-specific plant biomarkers, but are most useful when combined for their complimentary results.

Identifying a mysterious aquatic fern gametophyte

Suswassertang, a popular aquatic plant that is sold worldwide in aquarium markets, has been long considered a liverwort because of its ribbon-like thallus. However, its antheridia are remarkably fern-like in morphology. To corroborate the hypothesis that Suswassertang is a fern gametophyte and to determine its closest relative, we have sequenced five chloroplast regions (rbcL, accD, rps4–trnS, trnL intron, and trnL-F intergenic spacer), applying a DNA-based identification approach. The BLAST results on all regions revealed that Suswassertang is a polypod fern (order: Polypodiales) with strong affinities to the Lomariopsidaceae. Our phylogenetic analyses further showed that Suswassertang is nested within the hemi-epiphytic fern genus Lomariopsis (Lomariopsidaceae) and aligned very close to L. lineata. Our study brings new insights on the unexpected biology of Lomariopsis gametophytes—the capacity of retaining a prolonged gametophytic stage under water. It is of great interest to discover that a fern usually known to grow on trees also has gametophytes that thrive in water.

Complete chloroplast genome sequence of a tree fern Alsophila spinulosa: insights into evolutionary changes in fern chloroplast genomes

BackgroundFerns have generally been neglected in studies of chloroplast genomics. Before this study, only one polypod and two basal ferns had their complete chloroplast (cp) genome reported. Tree ferns represent an ancient fern lineage that first occurred in the Late Triassic. In recent phylogenetic analyses, tree ferns were shown to be the sister group of polypods, the most diverse group of living ferns. Availability of cp genome sequence from a tree fern will facilitate interpretation of the evolutionary changes of fern cp genomes. Here we have sequenced the complete cp genome of a scaly tree fern Alsophila spinulosa (Cyatheaceae).ResultsThe Alsophila cp genome is 156,661 base pairs (bp) in size, and has a typical quadripartite structure with the large (LSC, 86,308 bp) and small single copy (SSC, 21,623 bp) regions separated by two copies of an inverted repeat (IRs, 24,365 bp each). This genome contains 117 different genes encoding 85 proteins, 4 rRNAs and 28 tRNAs. Pseudogenes of ycf66 and trnT-UGU are also detected in this genome. A unique trnR-UCG gene (derived from trnR-CCG) is found between rbcL and accD. The Alsophila cp genome shares some unusual characteristics with the previously sequenced cp genome of the polypod fern Adiantum capillus-veneris, including the absence of 5 tRNA genes that exist in most other cp genomes. The genome shows a high degree of synteny with that of Adiantum, but differs considerably from two basal ferns (Angiopteris evecta and Psilotum nudum). At one endpoint of an ancient inversion we detected a highly repeated 565-bp-region that is absent from the Adiantum cp genome. An additional minor inversion of the trnD-GUC, which is possibly shared by all ferns, was identified by comparison between the fern and other land plant cp genomes.ConclusionBy comparing four fern cp genome sequences it was confirmed that two major rearrangements distinguish higher leptosporangiate ferns from basal fern lineages. The Alsophila cp genome is very similar to that of the polypod fern Adiantum in terms of gene content, gene order and GC content. However, there exist some striking differences between them: the trnR-UCG gene represents a putative molecular apomorphy of tree ferns; and the repeats observed at one inversion endpoint may be a vestige of some unknown rearrangement(s). This work provided fresh insights into the fern cp genome evolution as well as useful data for future phylogenetic studies.

Contrasting Predictors of Fern versus Angiosperm Decomposition in a Common Garden

ABSTRACTWe evaluated differences in the rates and correlates of decomposition among 32 fern and angiosperm litter types collected in Hawai'i. Leptosporangiate ferns were separated into groups based on phylogeny: ‘polypod’ ferns, a monophyletic clade of ferns that diversified in the Cretaceous, and all other (‘non‐polypod’) ferns that diversified earlier. We measured initial litter chemistry (nutrients and carbon chemistry), and mass loss and nitrogen (N), phosphorus (P), and calcium (Ca) of litter tissue during a 1‐yr incubation in a common garden. Nutrient concentrations and carbon (C) chemistry differed significantly among litter types, and litter turnover (k‐values) ranged from 0.29 to 8.31. Decomposition rates were more closely correlated with nutrient concentration than is typically observed. Lignin:N was the best predictor of decomposition across all litter types combined; however, among plant groups different predictors of decomposition were important. Nitrogen and P concentrations best predicted fern decomposition, whereas C chemistry, particularly lignin concentration, was more important for angiosperm (monocot and dicot) decomposition. Among native plants, non‐polypod ferns decomposed significantly more slowly than both polypod ferns and angiosperms. Contrary to our hypothesis, fern litter did not decompose more slowly than angiosperm litter overall. Nutrient dynamics in litter were affected by initial litter concentration more than phylogeny; low‐nutrient litter immobilized more nutrients than high‐nutrient litter. Systematic differences in rates of decomposition, and the importance of nutrients in predicting fern decomposition, imply that changes in species composition within ferns and between ferns and angiosperms could influence the functioning of ecosystems where ferns are important forest components.

Stoichiometry of ferns in Hawaii: implications for nutrient cycling

We asked if element concentrations in ferns differ systematically from those in woody dicots in ways that could influence ecosystem properties and processes. Phylogenetically, ferns are deeply separated from angiosperms; for our analyses we additionally separated leptosporangiate ferns into polypod ferns, a monophyletic clade of ferns which radiated after the rise of angiosperms, and all other leptosporangiate (non-polypod) ferns. We sampled both non-polypod and polypod ferns on a natural fertility gradient and within fertilized and unfertilized plots in Hawaii, and compared our data with shrub and tree samples collected previously in the same plots. Non-polypod ferns in particular had low Ca concentrations under all conditions and less plasticity in their N and P stoichiometry than did polypod ferns or dicots. Polypod ferns were particularly rich in N and P, with low N:P ratios, and their stoichiometry varied substantially in response to differences in nutrient availability. Distinguishing between these two groups has the potential to be useful both in and out of Hawaii, as they have distinct properties which can affect ecosystem function. These differences could contribute to the widespread abundance of polypod ferns in an angiosperm-dominated world, and to patterns of nutrient cycling and limitation in sites where ferns are abundant.