Ferns are one of the most diverse lineages of vascular plants, distributed widely in various habitats of tropical and subtropical forests. Previous studies have indicated that ferns tend to operate conservative stomatal behavior. However, this finding is difficult to explain the abundant fern species in open sites. This study aimed to clarify a whole-plant hydraulic strategy of tropical-subtropical ferns with different light requirements. We selected a total of 26 terrestrial fern species (14 light-demanding species and 12 shade-tolerant species) from the tropical-subtropical forests and measured their root (specific root length, SRL), stem (rhizome; rhizome biomass fraction, RHMF), and leaf hydraulic (pinna; hydraulic efficiency, drought tolerance, minimum leaf water potential, and safety margin) traits. In addition, we compiled a dataset of leaf hydraulic traits for woody and herbaceous angiosperm species from literatures. We analyzed the differences in safety margin between ferns and angiosperms, the root-stem-leaf traits relationships, and the contrasting whole-plant hydraulic strategies between light-demanding and shade-tolerant fern species. On average, ferns had more negative stomatal safety margin than woody and herbaceous angiosperm species. In addition, ferns showed lower leaf hydraulic safety margin than woody angiosperms. Below-ground traits significantly influenced leaf hydraulic safety in ferns, that is, species with lower SRL and higher RHMF showed higher water potential and leaf hydraulic safety margin. Compared to fern species from shade understory, light-demanding species were associated with higher SRL, lower RHMF, and higher leaf hydraulic risk. We conclude that tropical-subtropical ferns do not exhibit conservative leaf-level hydraulics but rely on a whole-plant strategy involving root acquisition and rhizome storage, which underlies their contrasting performance across light and water availability. This integrative view is crucial for predicting fern responses to habitat disturbance and climate change.
Ferns represent an evolutionarily distinct group of vascular plants and constitute an underexplored source of structurally diverse secondary metabolites with potential medicinal value. Several fern-derived compounds, including sesquiterpenes, triterpenes, flavonoids, phloroglucinol derivatives, lactones, and glycosides, have been associated with antibacterial, antidiabetic, analgesic, anticancer, hepatoprotective, neuroprotective, and other biological activities. However, despite their biochemical uniqueness and long-standing use in traditional medicine, ferns remain less extensively investigated than angiosperms as sources of bioactive compounds. In addition to their natural phytochemical diversity, the production of secondary metabolites in ferns may be influenced by abiotic stressors, such as light quality and intensity, temperature, salinity, drought, water availability, and mineral nutrition. Available studies indicate that selected abiotic stress conditions can enhance the accumulation of phenolic acids, flavonoids, polyphenols, carotenoids, and related compounds in several fern families, including Aspleniaceae, Athyriaceae, Dryopteridaceae, Onocleaceae, and Thelypteridaceae. Nevertheless, information on stress-induced modulation of metabolites that are unique or highly characteristic of ferns, particularly terpenes, terpene glycosides, and specific flavonoid derivatives, remains limited. This review summarizes the current knowledge on unique secondary metabolites in ferns, their reported medicinal properties, and the potential use of abiotic stress as an elicitation strategy to enhance their production. Overall, the review highlights ferns as promising but still insufficiently explored reservoirs of bioactive metabolites and identifies key directions for future phytochemical, pharmacological, and cultivation-based research.
Conjure an image of a fern in your mind. What is likely to fill the space is a large, lacy frond, illuminated by dappled light in a damp forest understory. You may also have been transported back in time millions of years ago, to a prehistoric landscape shrouded with ferns and dinosaurs. We often think of ferns as old, shade-loving, understory plants in temperate forests. While the lineage dates back 400 million years, and while many ferns do occupy such a niche, this evolutionary and ecological pigeonhole couldn't be further from the truth. Ferns are not hanging on by a thread in refugial environments - they are an evolutionary success story, persisting and diversifying into one of the most species-rich and biologically diverse groups of vascular plants, just behind the angiosperms. In this primer, I will expound on their evolutionary history, species richness, and modern ecological diversity, highlighting what they are and how they came to be.
The expansion or reduction of structural parts is an aspect of phenotypic variation that leads to diverse form (e.g. digits in vertebrates, segments in arthropods, or petals in angiosperms). The number of petiole vascular bundles (leaf traces) in ferns is one such structure. Integrating traditional anatomy and developmental videography with phylogenetic comparative methods, we examined the evolution and development of fern leaf traces. Across the eupolypods - 80% of extant species richness - and their sister lineages, we observe four conserved vascular developmental units (VDUs) that consistently give rise to three leaf trace architectures. Transitions between leaf traces occur at low and equal rates, with the possibility of reversions, suggesting no directional trend toward increasing trace number. While vascular area is inexorably linked with leaf size, the actual number of leaf traces does not significantly predict leaf size across ferns, meaning the same vascular area can be packed in many ways, and leaf size evolves relatively independent of trace number. These findings suggest that leaf trace architecture in ferns is determined by consistent VDUs and underscores how impressive diversity in leaf size and morphology can evolve within a framework of conserved vascular trace architectures.
In a survey of microfungi associated with ferns in southwestern China, two novel taxa and a new host record of the family Bionectriaceae, viz., Musananaesporium pronephrii sp. nov., Waltergamsia yunnanensis sp. nov. and Protocreopsis alba, were collected and introduced via morphological observations and multi-gene phylogenetic analyses of combined LSU, ITS, tef1-α, and rpb2 sequence dataset. These three species share key morphological features, including hyaline, simple conidiophores and phialidic conidiogenous cells that produce hyaline, slimy conidia. This study expands the known diversity of Bionectriaceae and represents the first record of Musananaesporium, Protocreopsis, and Waltergamsia species associated with ferns.
Ferns are most taxonomically and ecologically diverse in the tropics, but Cenozoic tropical fern fossils are rare, limiting understanding of fern evolution and biodiversity through time. Both Salvinia (Salviniaceae) and Acrostichum (Pteridaceae) are widely distributed ferns that are most diverse and abundant near the equator. Salvinia and Acrostichum macrofossils and spores have a rich Cenozoic record from subtropical and temperate regions, but only a handful of fossils have been discovered in the tropics, and few are from Asia. Here we report new fossil Salvinia and Acrostichum macrofossils and a diverse fern-spore assemblage from the early Eocene Ghazij Formation (Balochistan, Pakistan), palaeolatitude 0-5°N. As part of a larger study of the Ghazij flora, we collected 29 fern macrofossils and 39 palynology samples from multiple localities. The fern fossils were compared with similar extinct and extant vascular plants and systematically described. Salvinia dashtensis sp. nov. is described from four localities in the upper Ghazij Formation based on vegetative leaves, submerged rhizomorphic leaves, and inflated submerged structures (floats), along with Salvinia microspore massulae. These Salvinia occurrences serve as important freshwater palaeoenvironmental indicators. Acrostichum pinnae are identified at one locality in the upper Ghazij Formation from their characteristic reticulate secondary venation, forming rectangular to hexagonal polygons without freely ending veinlets. Acrostichumsporites spores are also identified. Spores of a total of 21 palynotaxa representing ten pteridophyte families (Gleicheniaceae, Lindsaeaceae, Lygodiaceae, Matoniaceae, Polypodiaceae, Pteridaceae, Osmundaceae, Schizaeaceae, Salviniaceae, and Thelypteridaceae) record a diverse fern assemblage from various ecological niches and the first occurrences of Pteris, Baculatisporites, and Verrucosisporites for Palaeogene Indo-Pakistan. The Salvinia and Acrostichum occurrences from the Ghazij Formation provide rare fossil examples of extant fern genera in the ancient tropics and represent some of the only fern fossils for all of Palaeogene tropical Asia.
The coordinated variation between plant size and functional traits is a critical link connecting individual ecological strategies and community assembly. However, unlike angiosperms, the drivers of trait-size coordination in coexisting fern species remain unclear. This study sampled seven coexisting fern species in a subtropical secondary forest, measuring biomass (an indicator of plant size) and functional traits related to leaf and root morphology and elemental composition. The coordinated relationship between plant individual size and functional traits was investigated using regression and principal component analysis, while the relative contributions of phylogeny, species identity, and individual biomass to trait variation were quantified via Bayesian phylogenetic generalized linear mixed models. Results indicated that there is a clear trait-size coordination relationship. Specifically, significant linear or nonlinear relationships were identified between plant size and multiple functional traits (e.g., elemental concentrations, specific leaf area, and specific root length), indicating a transition from "fast-acquisitive" to "conservative" strategies. However, variance partitioning indicated that phylogeny and species identity together explained the majority of variation in leaf and root traits (71.4% on average), whereas the independent contribution of individual biomass was minimal (7.1% on average). The results suggest that although significant trait-size coordination exists in understory fern communities, this coordination is statistically dominated by evolutionary history (phylogeny and species identity), though the ecological significance of plant size remains evident in significant trait-size coordination patterns. Overall, the coordinated variation between plant size and functional traits is pivotal in forging resource-allocation strategies and fostering fern species coexistence, highlighting that evolutionary background must be foregrounded when disentangling the mechanisms of functional community assembly.
The adaptation of native plants to metalliferous environments is associated with intricate plant-microbiome interactions. However, how co-occurring species assemble distinct rhizosphere microbiomes under extreme heavy metal(loid) stress remains unclear. Here, we report a field-based example of ecological divergence among three fern species under extreme antimony (Sb) stress. The Sb-accumulator Pteris multifida showed rhizosphere characteristics consistent with a "Biogeochemical Reactor", including higher abundances of the aioA and anoA genes (3.12- and 4.54-fold, respectively) and elevated Sb(V) content, which were 26.41% and 30.04% higher than those in the excluders. These characteristics coincided with a specialized co-occurrence network which, under high Sb stress, exhibits reduced complexity (16.20% fewer nodes), but an increased proportion of positive interactions, rising from 44.66% to 50.70%. In contrast, the excluder species exhibited characteristics consistent with "Biogeochemical filters," including a 2.91-fold higher abundance of the arsC gene and a reduced proportion of bioavailable Sb. Partial least squares path modeling further identified fern functional type, defined by their Sb accumulation strategy, and Sb valence state as significant direct factors associated with root Sb accumulation. Our findings propose a field-based ecological framework in which host-mediated rhizosphere differentiation may contribute to divergent Sb adaptation strategies, providing a foundation for microbiome-assisted phytomanagement of Sb-contaminated soils.
Unclear species boundaries are a common challenge in ecological studies and species inventories, obscuring patterns of biodiversity and complicating inferences about ecological and evolutionary processes. One possible cause of fuzziness is hybridisation, but little information exists on hybridisation in the tropics. Here we aim to address the question of potential hybridisation in the tropical American fern genus Trichomanes (Hymenophyllaceae) and to clarify evolutionary relationships within the genus. We take advantage of nuclear target-capture sequencing, haplotype phasing and off-target plastid reads to detect phylogenetic relationships and reticulate histories. We sampled 303 individuals that represent 41 known Trichomanes species. Our analyses recovered a robust backbone for the genus, strongly supporting subgenus Trichomanes as sister to subgen. Feea, and subgen. Davalliopsis as sister to subgen. Lacostea. Trichomanes pinnatum proved to be a complex where six different unnamed morphs represent four different kinds of evolutionary history. Two morphs appear to be stabilised, relatively old hybrid-derived species, one represents a recent hybrid, one reflects repeated spontaneous hybridisation between the same parent species, and one represents within-species morphological variation without any obvious genomic signal. Excluding the four hybrids makes T. pinnatum s.s. morphologically and genetically much more uniform, but its geographic distribution still covers practically all tropical America, indicating that the species may be approaching panmixia.
[This corrects the article DOI: 10.1002/aps3.11598.].
We investigated mercury uptake by the polypod fern Dryopteris filix-mas from two mercury emission sites in the Czech Republic along transects of high to low soil Hg concentrations, with the aim to determine whether ferns can accumulate Hg in above-ground biomass where it could disrupt meiotic processes. We focus on Hg because it has been hypothesized to have caused widespread malformation of spores in ferns proliferating in conjunction with one of the Big Five mass extinction events at the end of the Triassic (201.5 Ma). Here, we show that Hg-concentrations in the roots of Dryopteris filix-mas reflect Hg-contamination in the topsoils, while Hg-concentrations in above-ground foliage appears not directly related to topsoil contamination. We employed thermal desorption to determine that fern root systems mainly absorb Hg from soils while above-ground biomass may also have received Hg via gaseous atmospheric uptake. Further detailed Hg-concentration analyses of various fern parts led to the new insight that the highest levels of Hg reside in the spore-producing sori where it could in theory disrupt sporogenesis. To further examine the role of Hg in driving malformations, we isolated Dryopteris spores for microscopic inspection. However, no clear correlation was established between the relative abundance of aberrant spores and Hg-contamination in ferns or soils. Hence, other factors such as temperature, moisture availability, hybridization and other toxic metals likely also influenced fern reproduction. Nevertheless, the high bioaccumulation of Hg in the spore-producing sori should stimulate further research into the binding and influence of Hg by ferns and its role as a driver of plant sterility across mass extinction events.
Sexual reproduction in land plants involves diverse strategies for gamete production and fertilization, significantly differing between seed plants, which deliver sperm via pollen, and seed-free plants such as ferns, which produce motile sperm within specialized multicellular structures, antheridia, on independently growing gametophytes. Despite their crucial roles in sexual reproduction, the cellular mechanisms governing antheridium differentiation and male gametophyte development in ferns remain largely unexplored. Here, using non-invasive, time-lapse confocal imaging combined with computational three-dimensional analysis, we reconstructed detailed lineage maps of antheridium initiation, proliferation, and differentiation in the fern Ceratopteris richardii. Our findings demonstrate that antheridium development begins with highly conserved asymmetric cell divisions, giving rise to distinct sterile and spermatogenous cell lineages. Spermatogenous cells undergo synchronized and continuous proliferation, followed by programmed differentiation, eventually forming motile sperm released from mature antheridia. In contrast, the sterile lineage undergoes limited cell divisions, forming structural support tissues surrounding the spermatogenous core. Furthermore, quantitative analyses reveal the cellular basis underlying the previously reported antagonistic effects of the pheromone antheridiogen and abscisic acid on antheridium initiation and spermatogenous cell proliferation. These findings elucidate both conserved and lineage-specific mechanisms regulating sexual differentiation, providing comparative insights into reproductive strategies and hormone-mediated developmental processes across land plants.
As part of the Selaginellaceae treatment on the "Lycophytes and Ferns of Venezuela," led by Alan R. Smith (UC), ten new Selaginella species from northern South America, primarily found in Venezuela, are described. These include S. cataniapensis Valdespino, sp. nov., S. cultellifolia Valdespino & C.López, sp. nov., (also present in Colombia), S. guaramacalensis Valdespino & C.López, sp. nov., S. liesneri Valdespino, sp. nov., S. mawarinumensis Valdespino & C.López, sp. nov., S. monoloba A.R.Sm. ex C.López, Valdespino & Mostacero, sp. nov. (also present in Colombia), S. mostaceroi Valdespino & C.López, sp. nov., S. plagiochiloides Valdespino & C.López, sp. nov., S. tricula A.R.Sm. ex Valdespino & C.López, sp. nov., and S. turingiana Valdespino, sp. nov. Additionally, S. anemosyra Valdespino, nom. et stat. nov., is described and recognized at the species level, based on S. flabellata var. latifrons A.Braun. The new species are diagnosed using comparative morphology and contrasted with morphologically similar and closely related species. For each taxon, we provide illustrations from digitized herbarium material and scanning electron micrographs, along with preliminary conservation assessments using the IUCN categories and criteria. ResumenComo parte del tratamiento de las Selaginellaceae para “Lycophytes and Ferns of Venezuela”, liderado por Alan R. Smith (UC), se describen diez nuevas especies de Selaginella del norte de América del Sur, principalmente de Venezuela. Estas incluyen S. cataniapensis Valdespino, sp. nov., S. cultellifolia Valdespino & C.López, sp. nov. (también presente en Colombia), S. guaramacalensis Valdespino & C.López, sp. nov., S. liesneri Valdespino, sp. nov., S. mawarinumensis Valdespino & C.López, sp. nov., S. monoloba A.R.Sm. ex C.López, Valdespino & Mostacero, sp. nov. (también presente en Colombia), S. mostaceroi Valdespino & C.López, sp. nov., S. plagiochiloides Valdespino & C.López, sp. nov., S. tricula A.R.Sm. ex Valdespino & C.López, sp. nov., y S. turingiana Valdespino, sp. nov. Además, se describe y se reconoce a nivel de especie S. anemosyra Valdespino, nom. et stat. nov., basada en S. flabellata var. latifrons A.Braun. Las nuevas especies se diagnostican mediante la morfología comparativa y se contrastan con especies morfológicamente similares y estrechamente relacionadas. Para cada taxón, proporcionamos ilustraciones de material de herbario digitalizado y micrografías electrónicas de barrido, junto con evaluaciones preliminares de conservación basadas en las categorías y criterios de la UICN.
This study compiles and updates the checklist of ferns and lycophytes from the Sierra Madre Oriental (SMOR), Mexico. We analyzed the distribution and richness of these groups of seedless vascular plants to ensure the accuracy and reliability of the data. We reviewed information on these taxa from regional floristic studies, field explorations, and herbarium specimens. Our updated list includes 567 species, of which 511 are ferns and 56 lycophytes, organized into 37 families and 137 genera. The five most species-rich families are Pteridaceae (131), Polypodiaceae (76), Dryopteridaceae (68), Aspleniaceae (45), and Selaginellaceae (41). The five most species-rich genera are Asplenium (42), Elaphoglossum (30), Pleopeltis (24), Myriopteris (22), and Selaginella (21). The Mexican states with the greatest species richness within the SMOR are Puebla (423), Hidalgo (322), Querétaro (227), and Tamaulipas (181). The five grid cells with the highest richness, each containing more than 190 species, are situated in the southern part of the SMOR (Puebla and adjacent parts of Veracruz). The physiographic provinces with the greatest diversity are Carso Huasteco and the Gran Sierra Plegada, with 523 and 175 species, respectively. Latitudinal analysis indicated low richness at the northern extreme (28 °- 29 ° N, 11 species) and high richness at the southern extreme (19 °- 20 ° N, 469 species), with a notable peak at 24 °- 25 ° N (350 species). The highest diversity within elevation intervals occurs at 1,000-1,500 m (455 species). The SMOR contains 22 species of the pteridoflora classified under various risk categories according to the Mexican Official Norm NOM-059-SEMARNAT-2010, including seven listed on the IUCN Red List and ten protected under CITES. The taxonomic diversity index shows that the SMOR is among Mexico's most species-rich mountain ranges. The species richness documented here in the SMOR accounts for 50-54% of the pteridophyte diversity recorded in Mexico, increasing to 59.3% based on recent floristic studies conducted in the region.
Change in the haploid chromosome number commonly generates reproductive isolation between diverging species. If changes to the haploid chromosome number (karyotype) most often generate new species, variation in the rate of chromosome number evolution is expected to predict variation in diversification rates. While this correlation has been supported in some plants, we know less about how the mode and tempo of karyotype change evolve. Methods to address the evolution of diversification and chromosome number transition rates are computationally expensive and analyses are typically restricted to small clades or avoided all together. We identify and describe variation in the mode and tempo of karyotype evolution (via dysploidy and polyploidy) in the Polypodiales-a species and karyotype-rich order of ferns-by extending the Chromosome Number and Hidden State-dependent Speciation and Extinction model (ChromoHiSSE) to include whole genome duplication. Using the extended ChromoHiSSE model we estimate rates of karyotype evolution across 962 leptosporangiate ferns of the Polypodiales. We recover two hidden modes of chromosome number evolution between which the rates of karyotype evolution differ by more than an order of magnitude. Our rate estimates and the stochastic mapping of these modes across fern evolution suggests lineages with high karyotype lability are less likely to persist in the long-term. These results reinforce the theory that modern fern diversity is shaped substantially by polyploid speciation but challenge the expectation that diversification rates are enhanced by karyotype-driven reproductive isolation.
Over the last decade there have been significant advances in genome sequencing and model species development for ferns, lycophytes, and the bryophyte lineages-mosses, liverworts, and hornworts. This has facilitated research on the biosynthesis and function of flavonoids in these non-seed land-plant lineages. Most studies have been on the liverwort model species Marchantia polymorpha (Marchantia). There has been extensive characterisation of biosynthetic and regulatory genes of the Marchantia flavonoid pathway, including generation of loss-of-function mutant lines to examine flavonoid contribution to tolerance of abiotic stresses and pathogen infection. Notably, the red pigments of liverworts were shown to be a new class of flavonoids, named 'auronidins'. There are relatively few studies on mosses, lycophytes, or ferns. Yet these lineages also contain distinct red pigment structures not found in seed plants. They also contain novel enzymatic activities, unique horizontal gene transfer events, and expanded gene families for proteins such as the polyphenol oxidases. Additionally, the hornworts have been shown to have lost the flavonoid pathway during lineage-specific evolution. Indeed, evidence suggests that aspects of flavonoid biosynthesis may have been lost and regained on multiple occasions, in different lineages, during land plant evolution. In this review, we summarise recent advances in understanding of flavonoid biosynthesis in non-seed plants and examine how this informs theories of the evolution of the flavonoid pathway across the land-plant lineages.
Fern gametophytes represent a key phase in the fern life cycle and play an essential role in establishment and persistence. Despite their ecological and developmental relevance, the molecular basis of gametophyte function remains poorly characterised, particularly in apogamous ferns. The growing availability of transcriptomic resources offers new opportunities to investigate the functional organisation of this life stage. We conducted an in silico analysis of a previously published RNA-seq dataset obtained from gametophytes of the apogamous fern Dryopteris affinis ssp. affinis, focusing on a curated subset of protein candidates defined by stringent filtering criteria (E-value < 1 × 10⁻¹⁰⁰ and minimum sequence length > 450 bp). Following filtering, 1,160 proteins were retained and classified into three main functional categories-light-related processes, transport functions, and stress responses-representing key processes underlying gametophyte physiology and environmental adaptation. Light-associated proteins were primarily linked to photosynthesis, photorespiration, xanthophyll metabolism and photomorphogenesis, including components involved in photosystem assembly, chloroplast function and photoreceptor-mediated signalling. Transport-related proteins comprised a diverse set of membrane- and cytoplasm-associated transporters mediating the movement of sugars, amino acids, ions and other metabolites. In addition, numerous proteins associated with biotic and abiotic stress responses and plant immunity were detected. Protein-protein interaction analysis identified a small number of highly connected nodes, with MODIFIED TRANSPORT TO THE VACUOLE 1 (MTV17) emerging as the most connected protein, mainly supported by database- and text-mining-based evidence, suggesting a potential central role in intracellular transport-related processes. This study presents a curated, high-confidence protein dataset that extends current knowledge of fern gametophyte molecular organisation. The functional categories and interaction patterns identified highlight core processes underlying gametophyte physiology and stress adaptation, and provide a resource for future functional, comparative and experimental studies in ferns and other early-diverging land plants.
Ferns are well known for their exceptionally large genomes and high chromosome numbers, which may be in part due to whole genome duplications (WGDs) followed by slow diploidization. To better understand the mode of fern genome evolution, we focus on the heterosporous fern genus Salvinia, which exhibits striking variation in genome size and chromosome number. We generated chromosome-level genome assemblies for Salvinia cucullata, the fern with the smallest genome, and Salvinia molesta, a globally invasive species widely thought to be an allopentaploid. Surprisingly, we found that S. molesta is in fact a diploid hybrid and that S. cucullata, despite having a genome ten times smaller than S. molesta, has substantially more chromosomes. Both species lack any recent WGDs and their highly variable genomes were predominately shaped by transposable element proliferation and chromosome rearrangements. The complete decoupling of chromosome number and genome size in Salvinia sharply contrasts the typical pattern in ferns, which are mostly homosporous and produce only one type of spore by meiosis. Many of the genome features observed in Salvinia are consistent with genomic changes due to female meiotic drive, a mechanism possible only in heterosporous plants that produce distinct microspores and megaspores. These results redefine the genetic identity of S. molesta and provide insights into its invasive success. The marked variation in genome composition and structure within Salvinia challenges the prevailing model of fern genome evolution while aligning with expectations for angiosperms, another heterosporous lineage.
Climate change and human activities are increasing the frequency of megafires in savanna landscapes, affecting biodiversity and human livelihoods. In the savanna landscapes of the central Cerrado, within the iconic Chapada dos Veadeiros National Park, a megafire spread out-of-control during the 2017 extreme drought event, penetrating even the fire-sensitive riparian forests, and causing severe tree mortality. Here, we studied the impact and recovery of these riparian forests up to four years after the megafire. Using 36 field plots in burnt and unburnt riparian forests, we monitored vegetation and soil recovery, assessing structural and compositional changes over time. We tested the hypothesis that severely burnt forests could remain trapped in an open, grassy degraded state due to self-reinforcing feedbacks. Our results show that four years after the megafire, burnt flooded forests still showed structural and diversity losses relative to unburnt forests, with 80.1% lower tree density, 44.1% lower canopy cover, 64.5% lower aboveground biomass and 68.5% lower species richness. In these severely burnt forests, tree recruitment remained low, likely constrained by the increased cover of exotic grasses, which rose from 0.62% to 18.85%, and by invasive ferns, which increased from no recorded cover to 16.20% four years after fire. Analysis of tree composition suggest the process of biotic homogenization in burnt flooded forests, likely reflecting the novel sparse-tree habitats that persist in the riparian landscapes. Forest recovery was heterogeneous across study sites and primarily depended on fire severity. Our findings indicate that self-reinforcing feedbacks may have arrested the burnt riparian forests in an open degraded state after the megafire, due to a combination of soil erosion and persistent cover of invasive grasses and opportunistic ferns. Restoring forest successional trajectories requires interventions to disrupt these feedbacks and facilitate forest recovery. With the intensification of climate change, megafires will become more frequent in tropical savanna landscapes, threatening the persistence of riparian forests, with catastrophic social-ecological consequences.
The blastocladialean fungus Paraphysoderma sedebokerense is a devastating pathogen of unicellular green algae, that hinders their commercial cultivation. It is sister to Physoderma, a genus encompassing pathogens of ferns and angiosperms that causes major crop losses on Fabaceae and maize. Depending on favourable or unfavourable growth conditions, P. sedebokerense switches between vegetative, thin-walled cysts and resting, thick-walled cysts. Here, we identify P. sedebokerense novel life stages, including endobiotic structures inside algal host cells, yellow propagules and multiflagellated zoospores. This led us to reevaluate its life cycle and hypothesize the existence of facultative gametes developing parthenogenetically in the absence of fertilisation. Via the investigation of P. sedebokerense development without its host, we unveil that parthenogenetic, saprotrophic development occurs during the epibiotic life stage. Finally, we show that there is aggregation of P. sedebokerense propagules on the algal host cells and validate a low-cost, high-throughput cell-classification method to quantify this non-random spatial distribution at low prevalence of infection. In the future, identifying ways to disrupt aggregation would block infection at the earliest stages of an outbreak, providing algal farmers with an efficient route to manage this pathogen. We also provide evidence that the life cycle of P. sedebokerense much more closely resembles the life cycle of Physoderma spp. than previously thought; this implies that Paraphysoderma (and the protocols developed here) might be used as a convenient in vitro model to test the efficacy of treatments against devastating Physoderma pathogens.