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Background and AimsPatterns of morphological evolution at levels above family rank remain underexplored in the ferns. The present study seeks to address this gap through analysis of 79 morphological characters for 81 taxa, including representatives of all ten families of eupolypod II ferns. Recent molecular phylogenetic studies demonstrate that the evolution of the large eupolypod II clade (which includes nearly one-third of extant fern species) features unexpected patterns. The traditional ‘athyrioid’ ferns are scattered across the phylogeny despite their apparent morphological cohesiveness, and mixed among these seemingly conservative taxa are morphologically dissimilar groups that lack any obvious features uniting them with their relatives. Maximum-likelihood and maximum-parsimony character optimizations are used to determine characters that unite the seemingly disparate groups, and to test whether the polyphyly of the traditional athyrioid ferns is due to evolutionary stasis (symplesiomorphy) or convergent evolution. The major events in eupolypod II character evolution are reviewed, and character and character state concepts are reappraised, as a basis for further inquiries into fern morphology.MethodsCharacters were scored from the literature, live plants and herbarium specimens, and optimized using maximum-parsimony and maximum-likelihood, onto a highly supported topology derived from maximum-likelihood and Bayesian analysis of molecular data. Phylogenetic signal of characters were tested for using randomization methods and fitdiscrete.Key ResultsThe majority of character state changes within the eupolypod II phylogeny occur at the family level or above. Relative branch lengths for the morphological data resemble those from molecular data and fit an ancient rapid radiation model (long branches subtended by very short backbone internodes), with few characters uniting the morphologically disparate clades. The traditional athyrioid ferns were circumscribed based upon a combination of symplesiomorphic and homoplastic characters. Petiole vasculature consisting of two bundles is ancestral for eupolypods II and a synapomorphy for eupolypods II under deltran optimization. Sori restricted to one side of the vein defines the recently recognized clade comprising Rhachidosoraceae through Aspleniaceae, and sori present on both sides of the vein is a synapomorphy for the Athyriaceae sensu stricto. The results indicate that a chromosome base number of x =41 is synapomorphic for all eupolypods, a clade that includes over two-thirds of extant fern species.ConclusionsThe integrated approach synthesizes morphological studies with current phylogenetic hypotheses and provides explicit statements of character evolution in the eupolypod II fern families. Strong character support is found for previously recognized clades, whereas few characters support previously unrecognized clades. Sorus position appears to be less complicated than previously hypothesized, and linear sori restricted to one side of the vein support the clade comprising Aspleniaceae, Diplaziopsidaceae, Hemidictyaceae and Rachidosoraceae – a lineage only recently identified. Despite x =41 being a frequent number among extant species, to our knowledge it has not previously been demonstrated as the ancestral state. This is the first synapomorphy proposed for the eupolypod clade, a lineage comprising 67 % of extant fern species. This study provides some of the first hypotheses of character evolution at the family level and above in light of recent phylogenetic results, and promotes further study in an area that remains open for original observation.

The emergence of angiosperm-dominated tropical forests in the Cretaceous led to major shifts in the composition of biodiversity on Earth. Among these was the rise to prominence of epiphytic plant lineages, which today comprise an estimated one-quarter of tropical vascular plant diversity. Among the most successful epiphytic groups is the Polypodiaceae, which comprises an estimated 1500 species and displays a remarkable breadth of morphological and ecological diversity. Using a time-calibrated phylogeny for 417 species, we characterized macroevolutionary patterns in the family, identified shifts in diversification rate, and identified traits that are potential drivers of diversification. We find high diversification rates throughout the family, evidence for a radiation in a large clade of Paleotropical species, and support for increased rates of diversification associated with traits including chlorophyllous spores and noncordiform gametophytes. Contrary to previous hypotheses, our results indicate epiphytic species and groups with humus-collecting leaves diversify at lower rates than the family as a whole. We find that diversification rates in the Polypodiaceae are positively correlated with changes in elevation. Repeated successful exploration of novel habitat types, rather than morphological innovation, appears to be the primary driver of diversification in this group.

Phylogenetic divergence-time estimation has been revolutionized by two recent developments: 1) total-evidence dating (or \"tip-dating\") approaches that allow for the incorporation of fossils as tips in the analysis, with their phylogenetic and temporal relationships to the extant taxa inferred from the data and 2) the fossilized birth-death (FBD) class of tree models that capture the processes that produce the tree (speciation, extinction, and fossilization) and thus provide a coherent and biologically interpretable tree prior. To explore the behavior of these methods, we apply them to marattialean ferns, a group that was dominant in Carboniferous landscapes prior to declining to its modest extant diversity of slightly over 100 species. We show that tree models have a dramatic influence on estimates of both divergence times and topological relationships. This influence is driven by the strong, counter-intuitive informativeness of the uniform tree prior, and the inherent nonidentifiability of divergence-time models. In contrast to the strong influence of the tree models, we find minor effects of differing the morphological transition model or the morphological clock model. We compare the performance of a large pool of candidate models using a combination of posterior-predictive simulation and Bayes factors. Notably, an FBD model with epoch-specific speciation and extinction rates was strongly favored by Bayes factors. Our best-fitting model infers stem and crown divergences for the Marattiales in the mid-Devonian and Late Cretaceous, respectively, with elevated speciation rates in the Mississippian and elevated extinction rates in the Cisuralian leading to a peak diversity of ∼2800 species at the end of the Carboniferous, representing the heyday of the Psaroniaceae. This peak is followed by the rapid decline and ultimate extinction of the Psaroniaceae, with their descendants, the Marattiaceae, persisting at approximately stable levels of diversity until the present. This general diversification pattern appears to be insensitive to potential biases in the fossil record; despite the preponderance of available fossils being from Pennsylvanian coal balls, incorporating fossilization-rate variation does not improve model fit. In addition, by incorporating temporal data directly within the model and allowing for the inference of the phylogenetic position of the fossils, our study makes the surprising inference that the clade of extant Marattiales is relatively young, younger than any of the fossils historically thought to be congeneric with extant species. This result is a dramatic demonstration of the dangers of node-based approaches to divergence-time estimation, where the assignment of fossils to particular clades is made a priori (earlier node-based studies that constrained the minimum ages of extant genera based on these fossils resulted in much older age estimates than in our study) and of the utility of explicit models of morphological evolution and lineage diversification.

Hemiepiphytes have captured the attention of biologists since they seemingly hold clues to the evolution of epiphytes themselves. Hemiepiphytes are known to occur sporadically in the leptosporangiate ferns, but our understanding of their evolution remains limited by the relatively small number of detailed observations. This study adds to our knowledge by documenting seven species previously assumed to be holoepiphytes. This finding was based on fieldwork conducted in the Baining Mountains of Papua New Guinea that resulted in 319 collections representing 206 species. Approximately 3% of these species were hemiepiphytes: Asplenium acrobryum, A. amboinense, A. scandens, A. scolpendropsis, Crepidomanes aphlebioides, Leptochilus macrophyllus, and Sphaerostephanos scandens. All started growth as low-trunk epiphytes, and later, as larger climbing plants, exhibited strongly dimorphic roots consisting of short clasping ones that affixed the rhizome to the trunks and long feeding roots that entered the soil. Most of the seven hemiepiphyte species that we found exhibited distichous phyllotaxy and dorsiventrally flattened rhizomes, suggesting morphological convergence associated with this habit in four families. These new records suggest that large hemiepiphytic clades occur in Asplenium and Leptochilus. Our observations expand the geographic and taxonomic breadth of hemiepiphytic ferns, provide a baseline estimate of their diversity within a tropical flora, and offer morphological and phylogenetic clues to uncover additional records.

Field work conducted over the past fifteen years in the Sierra Juárez of Oaxaca, Mexico, has resulted in three new species of grammitid ferns and a new state distribution record. Two of the new species, Ceradenia sacksii and Lellingeria labiakii, are known only from the vicinity of Cerro Pelón and Humo Chico, in the Sierra Juárez. The third new species, Mycopteris martiniana, is also known from similar habitats in the states of Mexico and Veracruz. All three species are illustrated with line art and photographs and distinguished from their most similar relatives. The new record, Ceradenia margaritata, was previously known in Mexico from Chiapas. With these new additions, 37 species of grammitid ferns distributed in ten genera are now known from Mexico. Twenty eight of these species occur in Oaxaca, which remains the Mexican state with the overall highest diversity of ferns.

Aim: Gondwanan vicariance, boreotropical migration and long-distance dispersal have been posited as alternative hypotheses explaining the tropical distribution patterns and diversifications in many fern groups. Here, the historical biogeography of Diplazium is reconstructed to evaluate the impact of these biogeographical processes in shaping the modern tropical disjunctions. Location: World-wide with a focus on tropical forest habitats. Methods: Divergence times were estimated by analysing nucleotide sequences of seven plastid DNA regions (atpA, atpB, matK, rbcL, rps4, rps4-trnS and trnL-F) from 123 species of Diplazium and its allied genera, using a Bayesian relaxed clock method and three fossil calibrations. The ancestral areas were reconstructed using the likelihood dispersal—extinction—cladogenesis (DEC) approach. Results: The crown group of Diplazium was estimated to have originated in Eurasia and undergone an initial diversification in the Northern Hemisphere around 41.7 Ma [95% highest posterior density (HPD): 34-49 Ma] during the Eocene. Two disjunct events between the Old and New World were identified: one in subgenus Diplazium around the Eocene-Oligocene boundary (31.2 Ma, 95% HPD: 25-38 Ma), and the other in subgenus Callipteris during the middle Miocene (12.6 Ma, 95% HPD: 15-23 Ma). Furthermore, Palaeotropical disjunctions in subgenus Callipteris are indicative of multiple dispersal events during the Miocene. Main conclusions: The evolutionary history of Diplazium involves a variety of biogeographical scenarios. Early diversification of Diplazium in the Northern Hemisphere during the Eocene corresponds with the migration from Eurasia to North America over land bridges as a member of the boreotropical flora. The current tropical amphi-Pacific disjunctions in subgenus Diplazium can be better explained by the disruption of boreotropical belt, however, long-distance dispersal between Eurasia and tropical America cannot be ruled out. Islandhopping and trans-Pacific dispersals followed by speciation characterize the disjunctions and diversifications of subgenus Callipteris during the Neogene. Gondwanan vicariance is not supported by any of our results.

Premise of the Study Understanding the relationship between phenotypic evolution and lineage diversification is a central goal of evolutionary biology. To extend our understanding of the role morphological evolution plays in the diversification of plants, we examined the relationship between leaf size evolution and lineage diversification across ferns. Methods We tested for an association between body size evolution and lineage diversification using a comparative phylogenetic approach that combined a time‐calibrated phylogeny and leaf size data set for 2654 fern species. Rates of leaf size change and lineage diversification were estimated using BAMM, and rate correlations were performed for rates obtained for all families and individual species. Rates and patterns of rate–rate correlation were also analyzed separately for terrestrial and epiphytic taxa. Key Results We find no significant correlation between rates of leaf area change and lineage diversification, nor was there a difference in this pattern when growth habit is considered. Our results are consistent with the findings of an earlier study that reported decoupled rates of body size evolution and diversification in the Polypodiaceae, but conflict with a recent study that reported a positive correlation between body size evolution and lineage diversification rates in the tree fern family Cyatheaceae. Conclusions Our findings indicate that lineage diversification in ferns is largely decoupled from shifts in body size, in contrast to several other groups of organisms. Speciation in ferns appears to be primarily driven by hybridization and isolation along elevational gradients, rather than adaptive radiations featuring prominent morphological restructuring. The exceptional diversity of leaf morphologies in ferns appears to reflect a combination of ecophysiological constraints and adaptations that are not key innovations.

Acrospermum is a poorly known genus of epibiotic and saprophytic species with a subcosmopolitan distribution. Here, we investigate the intriguing relationship between Acrospermum and its host plants in the fern family Polypodiaceae, where it occurs upon approximately 45 neotropical species. We conducted phylogenetic analyses using an eight-marker comprehensive ascomycete data set comprising 719 species representing all major lineages along with 23 new Acrospermum specimens sampled from ferns. We ask whether fern-dwelling Acrospermum are monophyletic, whether epibiotic Acrospermum have evolved independently from saprophytic ancestors, and identify anamorphic phases by incorporating sequences for all suspected taxa. Our results corroborate the placement of Acrospermales within the Dothideomycetes with strong support. However, the order remains incertae sedis due to weak support along the branches subtending the clade that includes the Acrospermales plus Dyfrolomycetales. Our results show a strong phylogenetic pattern in lifestyles but do not clearly identify an ancestral life history state. The first divergence in Acrospermaceae splits fungicolous taxa from taxa that inhabit plants; saprophytes and anamorphic phases found on angiosperms occur in both clades. Fungicolous species are monophyletic, whereas species with an epibiotic or necrotic life history upon plants are nonmonophyletic due to the position of the saprophyte A. longisporium. Previously, all Acrospermum collected from ferns were identified as A. maxonii. Our results indicate that this is not monophyletic due to the inclusion of Gonatophragmium triuniae. Two species are described herein as A. gorditum, sp. nov., and A. leucocephalum, sp. nov. We find no instances of co-cladogenesis; however, our ability to detect this is limited by the lack of resolution in the A. maxonii clade. Rather, we see that that the distribution of epibiotic Acrospermum is explained by the overlap between the ecological niche of the Acrospermum species and its host.

Almost fifty years ago Dr. Rolla M. Tryon investigated the patterns of neotropical fern diversity and discovered that sites of exceptional richness and endemism are found in five predominantly montane regions. Here, we revisit these sites with the aid of contemporary methodologies. We integrate phylogenetic, ecological, climatic, and occurrence data to better understand what factors contribute to the patterns of fern diversity throughout the neotropics. With this dataset we are able to reassess Tryon's neotropical hotspots fifty years later and take one step closer to understanding the processes governing the distribution of fern species. We recover six hotspots of neotropical species richness and endemism that closely mirror those delineated by Tryon. Like Tryon, we find that hotspots are found predominantly in montane regions with more climatic space compared to surrounding areas. Patterns of species richness and lineage diversification can largely be explained by the extent of available habitats, especially in association with montane ecosystems. We also show that patterns of species assemblages across the neotropics are largely dictated by distance and elevation. In synthesis, we propose that, in addition to migration and persistence of relictual lineages, patterns of species richness and endemism in the neotropics are driven by in situ speciation in montane regions.

Functional traits determine how species interact with their abiotic and biotic environment. In turn, functional diversity describes how assemblages of species as a whole are adapted to their environment, which also determines how they might react to changing conditions. To fully understand functional diversity, it is fundamental to (a) disentangle the influences of environmental filtering and species richness from each other, (b) assess if the trait space saturates at high levels of species richness, and (c) understand how changes in species numbers affect the relative importance of the trait niche expansion and packing. In the present study, we determined functional diversity of fern assemblages by describing morphological traits related to resource acquisition along four tropical elevational transects with different environmental conditions and species richness. We used several functional diversity indices and their standardized effect size to consider different aspects of functional diversity. We contrasted these aspects of functional diversity with climate data and species richness using linear models and linear mixed models. Our results show that functional morphological trait diversity was primarily driven by species richness and only marginally by environmental conditions. Moreover, increasing species richness contributed progressively to packing of the morphological niche space, while at the same time decreasing morphological expansion until a saturation point was reached. Overall, our findings suggest that the density of co-occurring species is the fundamental driving force of morphological niche structure, and environmental conditions have only an indirect influence on fern resource acquisition strategies.