Structural motifs of syringyl peroxidases predate not only the gymnosperm-angiosperm divergence but also the radiation of tracheophytes

* The most distinctive variation in the monomer composition of lignins in vascular land plants is that found between the two main groups of seed plants. Thus, while gymnosperm lignins are typically composed of guaiacyl (G) units, angiosperm lignins are largely composed of similar levels of G and syringyl (S) units. * However, and contrary to what might be expected, peroxidases isolated from basal (Cycadales and Ginkgoales) and differentially evolved (Coniferales and Gnetales) gymnosperms are also able to oxidize S moieties, and this ability is independent of the presence or absence of S-type units in their lignins. * The results obtained led us to look at the protein database to search for homologies between gymnosperm peroxidases and true eudicot S-peroxidases, such as the Zinnia elegans peroxidase. * The findings showed that certain structural motifs characteristic of eudicot S-peroxidases (certain amino acid sequences and beta-sheet secondary structures) predate the gymnosperm-angiosperm divergence and the radiation of tracheophytes, since they are found not only in peroxidases from basal gymnosperms, ferns and lycopods, but also in peroxidases from the moss Physcomitrella patens (Bryopsida) and the liverwort Marchantia polymorpha (Marchantiopsida), which, as typical of bryophytes, do not have xylem tissue nor lignins.     

Divergent intron conservation in the mitochondrial nad2 gene: signatures for the three bryophyte classes (mosses,liverworts, and hornworts) and the lycophytes

The slow-evolving mitochondrial DNAs of plants have potentially conserved information on the phylogenetic branching of the earliest land plants. We present the nad2 gene structures in hornworts and liverworts and in the presumptive earliest-branching vascular land plant clade, the Lycopodiopsida. Taken together with the recently obtained nad2 data for mosses, each class of bryophytes presents another pattern of angiosperm-type introns conserved in nad2: intron nad2i1 in mosses; intron nad2i3 in liverworts; and both introns, nad2i3 and nad2i4, in hornworts. The lycopods Isoetes and Lycopodium show diverging intron conservation and feature a unique novel intron, termed nad2i3b. Hence, mitochondrial introns in general are positionally stable in the bryophytes and provide significant intraclade phylogenetic information, but the nad2 introns, in particular, cannot resolve the interclade relationships of the bryophyte classes and to the tracheophytes. The necessity for RNA editing to reconstitute conserved codon entities in nad2 is obvious for all clades except the marchantiid liverworts. Finally, we find that particularly small group II introns appear as a general feature of the Isoetes chondriome. Plant mitochondrial peculiarities such as RNA editing frequency, U-to-C type of RNA editing, and small group II introns appear to be genus-specific rather than gene-specific features.     

Distribution of introns in the mitochondrial gene nad1 in land plants: phylogenetic and molecular evolutionary implications

Forty-six species of diverse land plants were investigated by sequencing for their intron content in the mitochondrial gene nad1. A total of seven introns, all belonging to group II, were found, and two were newly discovered in this study. All 13 liverworts examined contain no intron, the same condition as in green algae. Mosses and hornworts, however, share one intron by themselves and another one with vascular plants. These intron distribution patterns are consistent with the hypothesis that liverworts represent the basal-most land plants and that the two introns were gained in the common ancestor of mosses-hornworts-vascular plants after liverworts had diverged. Hornworts also possess a unique intron of their own. A fourth intron was found only in Equisetum L., Marattiaceae, Ophioglossum L., Osmunda L., Asplenium L., and Adiantum L., and was likely acquired in their common ancestor, which supports the monophyly of moniliformopses. Three introns that were previously characterized in angiosperms and a few pteridophytes are now all extended to lycopods, and were likely gained in the common ancestor of vascular plants. Phylogenetic analyses of the intron sequences recovered topologies mirroring those of the plants, suggesting that the introns have all been vertically inherited. All seven nad1 group II introns show broad phylogenetic distribution patterns, with the narrowest being in moniliformopses and hornworts, lineages that date back to at least the Devonian (345 million years ago) and Silurian (435 million years ago), respectively. Hence, these introns must have invaded the genes via ancient transpositional events during the early stage of land plant evolution. Potentially heavy RNA editing was observed in nad1 of Haplomitrium Dedecek, Takakia Hatt. & Inoue, hornworts, Isoetes L., Ophioglossum, and Asplenium. A new nomenclature is proposed for group II introns.     

Basic peroxidases: The gateway for lignin evolution?

Lignins are cell wall phenolic heteropolymers which result from the oxidative coupling of three monolignols, p-coumaryl, coniferyl and sinapyl alcohol, in a reaction mediated by peroxidases. The most distinctive variation in the monomer composition of lignins in vascular plants is that found between the two main groups of seed plants. Thus, while gymnosperms lignins are typically composed of G units, with a minor proportion of H units, angiosperms lignins are largely composed of similar levels of G and S units. The presence of S units in angiosperm lignins raises certain concerns in relation with the step of lignin assembly due to the inability of most peroxidases to oxidize syringyl moieties. Zinnia elegans is currently used as a model for lignification studies: – first because of the simplicity and duality of the lignification pattern shown by hypocotyls and stems, in which hypocotyl lignins are typical of angiosperms, while young stem lignins partially resemble those occurring in gymnosperms. Secondly, because of the nature of the peroxidase isoenzyme complement, which is almost completely restricted to the presence of a basic peroxidase isoenzyme, which is capable of oxidizing both coniferyl and sinapyl alcohol, as well as both coniferyl and sinapyl aldehyde. In fact, the versatility of this enzyme is such that the substrate preference covers the three p-hydroxybenzaldehydes and the three p-hydroxycinnamic acids. The basic pI nature of this peroxidase is not an exceptional frame point in this system since basic peroxidases are differentially expressed during lignification in other model systems, show unusual and unique biochemical properties as regards the oxidation of syringyl moieties, and their down-regulation in transgenic plants leads to a reduction in lignin (G+S) levels. Basic peroxidase isoenzymes capable of oxidizing syringyl moieties are already present in basal gymnosperms, an observation that supports the idea that these enzymes were probably present in an ancestral plant species, pre-dating the early radiation of seed plants. It also suggests that the evolutionary gain of the monolignol branch which leads to the biosynthesis of sinapyl alcohol, and of course to syringyl lignins, was not only possible but also favored because the enzymes responsible for its polymerization had evolved previously. In this scenario, it is not surprising that these enzymes responsible for lignin construction appeared early in the evolution of land plants, and have been largely conserved during plant evolution. Abreviations: 4CL –p-hydroxycinnamate CoA ligase; C3H –p-coumarate-3-hydroxylase; C4H – cinnamate-4-hydroxylase; p-CA –p-coumaric acid; CAD – coniferyl alcohol dehydrogenase; CAld5H – coniferylaldehyde-5-hydroxylase; CCR –p-hydroxycinnamoyl-CoA reductase; CoI – compound I; CoII – compound II; G – guaiacyl unit; H –p-hydroxyphenyl unit; PAL – phenylalanine ammonia-lyase; S – syringyl unit.     

Phylogeny of early land plants: insights from genes and genomes

A large body of evidence from molecular systematic studies has confirmed the charophytic origin of land plants, and clarified monophyly of many lineages in charophytes and land plants. These studies have also identified liverworts as the earliest land plants, and the lycopods as the extant sister group to all other vascular plants. Two traditionally defined groups-bryophytes and pteridophytes-are now recognized as early grades of land plant evolution. However, several problems that complicate the use of sequence data in reconstructing plant phylogeny have become apparent; reconstruction of an accurate land plant phylogeny will require analysis of sequences of multiple genes and genomic structural characters of all three genomes.     

Multigene phylogeny of land plants with special reference to bryophytes and the earliest land plants

A widely held view of land plant relationships places liverworts as the first branch of the land plant tree, whereas some molecular analyses and a cladistic study of morphological characters indicate that hornworts are the earliest land plants. To help resolve this conflict, we used parsimony and likelihood methods to analyze a 6, 095-character data set composed of four genes (chloroplast rbcL and small-subunit rDNA from all three plant genomes) from all major land plant lineages. In all analyses, significant support was obtained for the monophyly of vascular plants, lycophytes, ferns (including PSILOTUM: and EQUISETUM:), seed plants, and angiosperms. Relationships among the three bryophyte lineages were unresolved in parsimony analyses in which all positions were included and weighted equally. However, in parsimony and likelihood analyses in which rbcL third-codon-position transitions were either excluded or downweighted (due to apparent saturation), hornworts were placed as sister to all other land plants, with mosses and liverworts jointly forming the second deepest lineage. Decay analyses and Kishino-Hasegawa tests of the third-position-excluded data set showed significant support for the hornwort-basal topology over several alternative topologies, including the commonly cited liverwort-basal topology. Among the four genes used, mitochondrial small-subunit rDNA showed the lowest homoplasy and alone recovered essentially the same topology as the multigene tree. This molecular phylogeny presents new opportunities to assess paleontological evidence and morphological innovations that occurred during the early evolution of terrestrial plants.     

Looking for syringyl peroxidases

Lignins are cell wall heteropolymers that arise from the peroxidase-mediated coupling of p-coumaryl, coniferyl and sinapyl alcohols. In gymnosperms, they are derived from coniferyl alcohol, whereas in angiosperms, lignins are derived from coniferyl and sinapyl alcohols. Thus, although it is frequently assumed that the chemical complexity of lignins has increased during plant evolution, it is frequently forgotten that pteridophytes have lignins that are derived from sinapyl alcohol. Until recently, most peroxidases characterized in flowering plants only oxidized coniferyl alcohol. However, recent reports have described the molecular characterization of peroxidases capable of oxidizing sinapyl alcohol (syringyl peroxidases). Current molecular studies propose that the structural motifs of syringyl peroxidases predate the radiation of tracheophytes, which suggests that syringyl peroxidases existed before the appearance of syringyl lignins.     

Exploring the plastid genome disparity of liverworts

Sequencing the plastid genomes of land plants provides crucial improvements to our understanding of the plastome evolution of land plants. Although the number of available complete plastid genome sequences has rapidly increased in the recent years, only a few sequences have been yet released for the three bryophyte lineages, namely hornworts, liverworts, and mosses. Here, we explore the disparity of the plastome structure of liverworts by increasing the number of sequenced liverwort plastomes from five to 18. The expanded sampling included representatives of all major lineages of liverworts including the genus Haplomitrium. The disparity of the liverwort genomes was compared with other 2386 land plant plastomes with emphasis on genome size and GC‐content. We found evidence for structural conservatism of the plastid genomes in liverworts and a trend towards reduced plastome sequence length in liverworts and derived mosses compared to other land plants, including hornworts and basal lineages of mosses. Furthermore, Aneura and Haplomitrium were distinct from other liverworts by an increased GC content, with the one found in Haplomitrium only second to the lycophyte Selaginella. The results suggest the hypothesis that liverworts and other land plants inherited and conserved the plastome structure of their most recent algal ancestors.     

Terrestrial surface stabilisation by modern analogues of the earliest land plants: A multi-dimensional imaging study

The evolution of the first plant-based terrestrial ecosystems in the early Palaeozoic had a profound effect on the development of soils, the architecture of sedimentary systems, and shifts in global biogeochemical cycles. In part, this was due to the evolution of complex below-ground (root-like) anchorage systems in plants, which expanded and promoted plant–mineral interactions, weathering, and resulting surface sediment stabilisation. However, little is understood about how these micro-scale processes occurred, because of a lack of in situ plant fossils in sedimentary rocks/palaeosols that exhibit these interactions. Some modern plants (e.g., liverworts, mosses, lycophytes) share key features with the earliest land plants; these include uni- or multicellular rhizoid-like anchorage systems or simple roots, and the ability to develop below-ground networks through prostrate axes, and intimate associations with fungi, making them suitable analogues. Here, we investigated cryptogamic ground covers in Iceland and New Zealand to better understand these interactions, and how they initiate the sediment stabilisation process. We employed multi-dimensional and multi-scale imaging, including scanning electron microscopy (SEM) and X-ray Computed Tomography (μCT) of non-vascular liverworts (Haplomitriopsida and complex thalloids) and mosses, with additional imaging of vascular lycopods. We find that plants interact with their substrate in multiple ways, including: (1) through the development of extensive surface coverings as mats; (2) entrapment of sediment grains within and between networks of rhizoids; (3) grain entwining and adherence by rhizoids, through mucilage secretions, biofilm-like envelopment of thalli on surface grains; and (4) through grain entrapment within upright ‘leafy’ structures. Significantly, μCT imaging allows us to ascertain that rhizoids are the main method for entrapment and stabilisation of soil grains in the thalloid liverworts. This information provides us with details of how the earliest land plants may have significantly influenced early Palaeozoic sedimentary system architectures, promoted in situ weathering and proto-soil development, and how these interactions diversified over time with the evolution of new plant organ systems. Further, this study highlights the importance of cryptogamic organisms in the early stages of sediment stabilisation and soil formation today.     

A comparison of alpha and beta diversity patterns of ferns,bryophytes and macrolichens in tropical montane forests of southern Ecuador

We present a first comparison of patterns of alpha and beta diversity of ferns, mosses, liverworts and macrolichens in neotropical montane rainforests, and explore the question whether specific taxa may be used as surrogates for others. In three localities in southern Ecuador, we surveyed terrestrial and epiphytic species assemblages in ridge and slope forests in 28 plots of 400 m2 each. The epiphytic habitat was significantly richer in ferns, liverworts, and macrolichens than the terrestrial habitat; mosses, however, were primarily terrestrial. Alpha diversity of ferns and of liverworts was congruent in both habitats. Mosses were similar to ferns and liverworts only in the epiphytic habitat. Macrolichens did not share patterns of alpha diversity with any other group. Beta diversity of ferns, mosses and liverworts (lichens excluded due to low species richness) was similar in the terrestrial habitat, but not in the epiphytic habitat. Our results demonstrate that patterns of alpha diversity of the studied taxa cannot be used to predict patterns of beta diversity. Moreover, diversity patterns observed in epiphytes are different from terrestrial plants. We noted a general coincidence in species patterns of liverworts and ferns. Diversity patterns of macrolichens, in contrast, were completely independent from any other taxonomic group studied.     

Evolutionary significance of isopreneemission from mosses

Isoprene emission has been documented and characterized from species in all major groups of vascular plants. We report in our survey that isoprene emission is much more common in mosses and ferns than later divergent land plants but is absent in liverworts and hornworts. The light and temperature responses of isoprene emission from Sphagnum capillifolium (Ehrh.) Hedw. are similar to those of other land plants. Isoprene increases thermotolerance of S. capillifolium to the same extent seen in higher plants as measured by chlorophyll fluorescence. Sphagnum species in a northern Wisconsin bog experienced large temperature fluctuations similar to those reported in tree canopies. Since isoprene has been shown to help plants cope with large, rapid temperature fluctuations, we hypothesize the thermal and correlated dessication stress experienced by early land plants provided the selective pressure for the evolution of light-dependent isoprene emission in the ancestors of modern mosses. As plants radiated into different habitats, this capacity was lost multiple times in favor of other thermal protective mechanisms.     

The invention of WUS-like stem cell-promoting functions in plants predates leptosporangiate ferns

The growth of land plants depends on stem cell-containing meristems which show major differences in their architecture from basal to higher plant species. In Arabidopsis, the stem cell niches in the shoot and root meristems are promoted by WUSCHEL (WUS) and WOX5, respectively. Both genes are members of a non-ancestral clade of the WUS-related homeobox (WOX) gene family, which is absent in extant bryophytes and lycophytes. Our analyses of five fern species suggest that a single WUS orthologue was present in the last common ancestor (LCA) of leptosporangiate ferns and seed plants. In the extant fern Ceratopteris richardii, the WUS pro-orthologue marks the pluripotent cell fate of immediate descendants of the root apical initial, so-called merophytes, which undergo a series of stereotypic cell divisions and give rise to all cell types of the root except the root cap. The invention of a WUS-like function within the WOX gene family in an ancestor of leptosporangiate ferns and seed plants and its amplification and sub-functionalisation to different stem cell niches might relate to the success of seed plants, especially angiosperms.     

Contributions of plant molecular systematics to studies of molecular evolution

Dobzhansky stated that nothing in biology makes sense except in the light of evolution. A close corollary, and the central theme of this paper, is that everything makes a lot more sense in the light of phylogeny. Systematics is in the midst of a renaissance, heralded by the widespread application of new analytical approaches and the introduction of molecular techniques. Molecular phylogenetic analyses are now commonplace, and they have provided unparalleled insights into relationships at all levels of plant phylogeny. At deep levels, molecular studies have revealed that charophyte green algae are the closest relatives of the land plants and suggested that liverworts are sister to all other extant land plants. Other studies have suggested that lycopods are sister to all other vascular plants and clarified relationships among the ferns. The impact of molecular phylogenetics on the angiosperms has been particularly dramatic – some of the largest phylogenetic analyses yet conducted have involved the angiosperms. Inferences from three genes (rbcL, atpB, 18S rDNA) agree in the major features of angiosperm phylogeny and have resulted in a reclassification of the angiosperms. This ordinal-level reclassification is perhaps the most dramatic and important change in higher-level angiosperm taxonomy in the past 200 years. At lower taxonomic levels, phylogenetic analyses have revealed the closest relatives of many crops and model organisms for studies of molecular genetics, concomitantly pointing to possible relatives for use in comparative studies and plant breeding. Furthermore, phylogenetic information has contributed to new perspectives on the evolution of polyploid genomes. The phylogenetic trees now available at all levels of the taxonomic hierarchy for angiosperms and other green plants should play a pivotal role in comparative studies in diverse fields from ecology to molecular evolution and comparative genetics.     

Phylogenetic relationships of land plants using mitochondrial small-subunit rDNA sequences

Phylogenetic relationships among embryophytes (tracheophytes, mosses, liverworts, and hornworts) were examined using 21 newly generated mitochondrial small-subunit (19S) rDNA sequences. The "core" 19S rDNA contained more phylogenetically informative sites and lower homoplasy than either nuclear 18S or plastid 16S rDNA. Results of phylogenetic analyses using parsimony (MP) and likelihood (ML) were generally congruent. Using MP, two trees were obtained that resolved either liverworts or hornworts as the basal land plant clade. The optimal ML tree showed hornworts as basal. That topology was not statistically different from the two MP trees, thus both appear to be equally viable evolutionary hypotheses. High bootstrap support was obtained for the majority of higher level embryophyte clades named in a recent morphologically based classification, e.g., Tracheophyta, Euphyllophytina, Lycophytina, and Spermatophytata. Strong support was also obtained for the following monophyletic groups: hornworts, liverworts, mosses, lycopsids, leptosporangiate and eusporangiate ferns, gymnosperms and angiosperms. This molecular analysis supported a sister relationship between Equisetum and leptosporangiate ferns and a monophyletic gymnosperms sister to angiosperms. The topologies of deeper clades were affected by taxon inclusion (particularly hornworts) as demonstrated by jackknife analyses. This study represents the first use of mitochondrial 19S rDNA for phylogenetic purposes and it appears well-suited for examining intermediate to deep evolutionary relationships among embryophytes.     

Evolution of Inbreeding and Outcrossing in Ferns and Fern-Allies

Abstract Mating systems of 18 species of homosporous ferns follow a bimodal distribution, similar to that observed for seed plants (Schemske and Lande, 1985). Most species are highly outcrossing, a few are inbreeding, and two species examined to date have mixed mating systems. Equisetum arvense and several species of lycopods are also highly outcrossing. Several mechanisms, including inbreeding depression, antheridiogen, and ontogenetic sequences that result in effectively unisexual gametophytes, promote outcrossing in homosporous ferns and perhaps other homosporous pteridophytes as well. In some species of homosporous ferns, selection has favored the evolution of inbreeding as an adaptation for colonization. High levels of intra- and interpopulational gene flow via spore dispersal, coupled with high levels of intergametophytic crossing, generally lead to genetically homogeneous populations and species of homosporous ferns. However, rock-dwelling ferns and ferns from xeric habitats may exhibit significant population genetic structure due to physically patchy habitats. Reticulate evolution in homosporous ferns may be enhanced by high levels of intergametophytic crossing.     

ABA in bryophytes: how a universal growth regulator in life became a plant hormone?

Abscisic acid (ABA) is not a plant-specific compound but one found in organisms across kingdoms from bacteria to animals, suggesting that it is a ubiquitous and versatile substance that can modulate physiological functions of various organisms. Recent studies have shown that plants developed an elegant system for ABA sensing and early signal transduction mechanisms to modulate responses to environmental stresses for survival in terrestrial conditions. ABA-induced increase in stress tolerance has been reported not only in vascular plants but also in non-vascular bryophytes. Since bryophytes are the key group of organisms in the context of plant evolution, clarification of their ABA-dependent processes is important for understanding evolutionary adaptation of land plants. Molecular approaches using Physcomitrella patens have revealed that ABA plays a role in dehydration stress tolerance in mosses, which comprise a major group of bryophytes. Furthermore, we recently reported that signaling machinery for ABA responses is also conserved in liverworts, representing the most basal members of extant land plant lineage. Conservation of the mechanism for ABA sensing and responses in angiosperms and basal land plants suggests that acquisition of this mechanism for stress tolerance in vegetative tissues was one of the critical evolutionary events for adaptation to the land. This review describes the role of ABA in basal land plants as well as non-land plant organisms and further elaborates on recent progress in molecular studies of model bryophytes by comparative and functional genomic approaches.     

A comparison of altitudinal species richness patterns of bryophytes with other plant groups in Nepal, Central Himalaya

Aim To explore species richness patterns in liverworts and mosses along a central Himalayan altitudinal gradient in Nepal (100–5500 m a.s.l.) and to compare these patterns with patterns observed for ferns and flowering plants. We also evaluate the potential importance of Rapoport’s elevational rule in explaining the observed richness patterns for liverworts and mosses. Location Nepal, Central Himalaya. Methods We used published data on the altitudinal ranges of over 840 Nepalese mosses and liverworts to interpolate presence between maximum and minimum recorded elevations, thereby giving estimates of species richness for 100‐m altitudinal bands. These were compared with previously published patterns for ferns and flowering plants, derived in the same way. Rapoport’s elevational rule was assessed by correlation analyses and the statistical significance of the observed correlations was evaluated by Monte Carlo simulations. Results There are strong correlations between richness of the four groups of plants. A humped, unimodal relationship between species richness and altitude was observed for both liverworts and mosses, with maximum richness at 2800 m and 2500 m, respectively. These peaks contrast with the richness peak of ferns at 1900 m and of vascular plants, which have a plateau in species richness between 1500 and 2500 m. Endemic liverworts have their maximum richness at 3300 m, whereas non‐endemic liverworts show their maximum richness at 2700 m. The proportion of endemic species is highest at about 4250 m. There is no support from Nepalese mosses for Rapoport’s elevational rule. Despite a high correlation between altitude and elevational range for Nepalese liverworts, results from null simulation models suggest that no clear conclusions can be made about whether liverworts support Rapoport’s elevational rule. Main conclusions Different demands for climatic variables such as available energy and water may be the main reason for the differences between the observed patterns for the four plant groups. The mid‐domain effect may explain part of the observed pattern in moss and liverwort richness but it probably only works as a modifier of the main underlying relationship between climate and species richness.     

Plant-type N-glycans containing fucose and xylose in Bryophyta (mosses) and Tracheophyta (ferns)

The presence of typical plant-type N-glycans (eg, M3FX, Gn2M3FX, and Le(a)2M3FX) in mosses, ferns, and other organisms was examined to determine which plant initially acquired glycosyltransferases to produce plant-type N-glycans during organic evolution. No M3FX-type N-glycan was detected in lichens (Cladonia humilis) or in any one of the three preland plants Enteromorpha prolifera, Ulva pertusa Kjellman, and Chara braunii Gmelin. In Bryophyta, M3FX-type N-glycan was detected at trace amounts in Anthocerotopsida (hornworts) and at certain amounts in Bryopsida (mosses), but not in Hepaticopsida (liverworts). Le(a)2M3FX was detected in some Bryopsida of relatively high M3FX content. Most Tracheophyta (ferns and higher plants) contained the three typical M3FX-type glycans as the main N-glycans in different ratios. These results suggest that organisms acquired xylosyltransferase and fucosyltransferase during the development of mosses from liverworts, and that later all plants retained both enzymes. Bryopsida have also obtained galactosyltransferase and fucosyltransferase to synthesize the Le(a) antigen.     

Spatial genetic analyses reveal strong genetic structure in two populations of the outcrossing tree fern Alsophila firma (Cyatheaceae)

The development of spatial genetic structure (SGS) in seed plants has been linked to several biological attributes of species, such as breeding system and life form. However, little is known about SGS in ferns, which together with lycopods are unique among land plants in having two free‐living life stages. We combined spatial aggregation statistics and spatial genetic autocorrelation analyses using five plastid microsatellites and one nuclear gene to investigate SGS in two populations of the outcrossing tree fern Alsophila firma (Cyatheaceae). We assessed how the observed patterns compare with those estimated for other ferns and seed plants. Populations of A. firma exhibited strong SGS, spatial clustering of individuals, substantial clonal diversity and no inbreeding. SGS in ferns appears to be higher than in most seed plants analysed to date. Contrary to our expectations, an outcrossing breeding system, wind dispersal and an arborescent life form did not translate into weak or no SGS. In ferns, SGS is probably being affected by the life cycle with two free‐living life stages. The reproductive biology of ferns appears to be more complex than previously thought. This implies that SGS in ferns is affected by some factors that cannot be inferred from the study of flowering plants. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 439–449.