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Ferns and fern allies have low photosynthetic rates compared with seed plants. Their photosynthesis is thought to be limited principally by physical CO2 diffusion from the atmosphere to chloroplasts. The aim of this study was to understand the reasons for low photosynthesis in species of ferns and fern allies (Lycopodiopsida and Polypodiopsida). We performed a comprehensive assessment of the foliar gas-exchange and mesophyll structural traits involved in photosynthetic function for 35 species of ferns and fern allies. Additionally, the leaf economics spectrum (the interrelationships between photosynthetic capacity and leaf/frond traits such as leaf dry mass per unit area or nitrogen content) was tested. Low mesophyll conductance to CO2 was the main cause for low photosynthesis in ferns and fern allies, which, in turn, was associated with thick cell walls and reduced chloroplast distribution towards intercellular mesophyll air spaces. Generally, the leaf economics spectrum in ferns follows a trend similar to that in seed plants. Nevertheless, ferns and allies had less nitrogen per unit DW than seed plants (i.e. the same slope but a different intercept) and lower photosynthesis rates per leaf mass area and per unit of nitrogen.

Understanding how the remarkable biodiversity of the American tropics developed has been a long‐standing question, yet knowledge gaps remain. Previous studies examined the roles of bioregions in shaping diversity patterns but often overlooked speciation, a critical driver of species richness, and insufficiently accounted for temporal changes in speciation and dispersal dynamics. To address this, we investigated the temporal mechanisms of speciation and dispersal that have shaped diversity in the American tropics using ferns (Polypodiopsida) as a model group across nine bioregions. We employed biogeographic stochastic mapping (BSM) and a large‐scale phylogenetic tree alongside extensive occurrence records to infer historical patterns of speciation and dispersal. We find that the American tropics function as a biogeographical maze composed of interconnected corridors, characterised by high emigration and immigration rates, rather than isolated regions. The Andes emerged prominently as a biodiversity radiator, playing a dual role by generating substantial species richness through speciation and acting as a primary source of dispersal to neighbouring regions. This unique position underscores the Andes' pivotal role in structuring fern diversity across the American tropics, contrasting with the Amazonian‐centred patterns typically observed in angiosperms. Our findings highlight the critical importance of considering speciation and historical contexts in relation to changing environments when interpreting patterns of tropical biodiversity.

Asplenium (Aspleniaceae) is taxonomically one of the most complex fern genera with about 700 species, nearly cosmopolitan in distribution. In Argentina, Asplenium constitutes the most speciesrich fern genus, with 38 taxa. Among these species, the delimitation of Asplenium achalense remain poorly understood. Some authors consider A. serra as a variant of A. achalense, or even the last species has been considered as a complex of species. The finding of a population of Asplenium achalense in Yungas after three decades without observations in the wild and neither registering more recently herbarium specimens, made it possible to analyse living material and observe new diagnostic characters present in rachises and laminae scales, glandular hairs in petioles and rachises along with spore wall features, that are critical to delimitate A. achalense as a well-defined taxon, endemics of north-west to central Argentina. Asplenium (Aspleniaceae) es uno de los géneros de helechos más complejos desde el punto de vista taxonómico, con unas 700 especies, de distribución casi cosmopolita. En Argentina, Asplenium constituye el género de helechos más rico en especies, con 38 taxones. Entre esas especies, la delimitación de Asplenium achalense sigue estando escasamente comprendida. Algunos autores consideran a A. serra como una variante de A. achalense, o incluso la última especie ha sido considerada como un complejo de especies. El hallazgo de una población de Asplenium achalense en Yungas después de tres décadas sin observaciones en la naturaleza y de no registrarse ejemplares de herbarios más recientes, hizo posible analizar material vivo y observar nuevos caracteres diagnósticos presentes en raquis y escamas de láminas, pelos glandulares en pecíolos y raquis, junto con características de la pared de las esporas, que son críticos para delimitar A. achalense como un taxón bien definido, endémico del Noroeste hasta el centro de Argentina.

The tremendously unbalanced distribution of species richness across clades in the tree of life is often interpreted as the result of variation in the rates of diversification, which may themselves respond to trait evolution. Even though this is likely a widespread pattern, not all diverse groups of organisms exhibit heterogeneity in their dynamics of diversification. Testing and characterizing the processes driving the evolution of clades with steady rates of diversification over long periods of time are of importance in order to have a full understanding of the build-up of biodiversity through time. We studied the macroevolutionary history of the species-rich tree fern family Cyatheaceae and inferred a time-calibrated phylogeny of the family including extinct and extant species using the recently developed fossilized birth-death method. We tested whether the high diversity of Cyatheaceae is the result of episodes of rapid diversification associated with phenotypic and ecological differentiation or driven by stable but low rates of diversification. We compared the rates of diversification across clades, modelled the evolution of body size and climatic preferences and tested for trait-dependent diversification. This ancient group diversified at a low and constant rate during its long evolutionary history. Morphological and climatic niche evolution were found to be overall highly conserved, although we detected several shifts in the rates of evolution of climatic preferences, linked to changes in elevation. The diversification of the family occurred gradually, within limited phenotypic and ecological boundaries, and yet resulted in a remarkable species richness. Our study indicates that Cyatheaceae is a diverse clade which slowly accumulated morphological, ecological and taxonomic diversity over a long evolutionary period and provides a compelling example of the tropics as a museum of biodiversity.

New combinations are made for several ferns in the Hawaiian Islands in the genera Asplenium, Cystopteris, Dicranopteris, and Microlepia: Asplenium dielerectum f. alexandri comb. nov., Cystopteris douglasii var. sandwicensis, stat. and comb. nov., Dicranopteris linearis var. emarginata comb. nov., and Microlepia setosa var. mauiensis comb nov. A new nothogenus, 3Christelliopsis nothogen. nov. is named for hybrids between Christella and Menisciopsis and a new combination, 3Christelliopsis palmeri comb. nov. is made for the hybrid Christella dentata 3 Menisciopsis cyatheoides.

We present the first records of Lindsaea leprieurii Hook. and Lindsaea angustipinna A.Rojas & Tejero from Panama. Images, taxonomic comments, conservation assessments, and geographic notes are provided.

In this paper a comprehensive list of Icelandic ferns (Polypodiopsida sensu PPG I) is presented alongside detailed distribution maps (5×5 km grid). Apart from general characteristics of the local range, details on ecology and conservation status are provided, including most common habitat types for each species, altitudinal range and a local red list status assessment according to IUCN criteria. The most important bibliography records for each species are also listed.

The complicated nomenclatural history of the extinct fossil-genera Acitheca and Strephopteris (fertile foliage) and Polymorphopteris (sterile foliage), established for fossil ferns (Marattiopsida), is reviewed and corrected with new bibliographic and historical data. Strephopteris as a generic name established for fertile foliage of Acitheca-type has priority, but due to the long and widespread use of Acitheca it was recently proposed to reject it in favour of the established name Acitheca. Since Acitheca as a fossil-genus was established for distinctive fertile foliage, but its currently accepted type, A. polymorpha (≡ Pecopteris polymorpha), was founded on sterile foliage, it is proposed to reject this type and return to the earlier concept of Sterzel who thought that Acitheca was typified by the fossil-species Scolecopteris conspicua, based on fertile foliage. This procedure requires official conservation of the type. Correction of the type allows continuing the current use of another fossil-genus, Polymorphopteris, which was inadvertently validated on the same type as Acitheca. The legitimization of the fossil-genus Polymorphopteris, based on sterile foliage only, will stabilize the current established systematics of fossil marattiopsid remains, for which no fertile organs are known. Since Scolecopteris conspicua, when established as a fertile counterpart of sterile foliage known as Pecopteris polymorpha, originally included two unrelated archetypes of fertile foliage, known as compressions and petrifactions, the typification of the fossil-species by fossil specimens known as compressions allows continued use of Acitheca as a distinct fossil-genus for fertile foliage as compressions. The petrifactions formerly attributed to A. polymorpha from younger sediments (Lower Permian) of France are re-considered as a distinct fossilspecies, Scolecopteris renaultii sp. nov. The formerly not validly published fossil-genus Bifariusotheca for Acitheca-like fossils from the Permian of China is validated. Kamatheca is validated for the aberrant Angaridan fossil-species, Acitheca gigantea. Nine not validly published fossil-species of Polymorphopteris are validated to follow modern circumscription of the fossil-genus: Polymorphopteris cistii comb. nov., P. gothanii comb. nov., P. integra comb. nov., P. magdalenae sp. nov., P. multifurcata comb. nov., P. oblongifolia comb. nov., P. pseudobucklandii comb. nov., P. pseudointegra comb. nov., and P. wagneri sp. nov. Callipteridium subelegans and Scolecopteris conspicua are neotypified; Acitheca isomorpha and Pecopteris cistii are lectotypified. As an addition to Taxonomic literature II records, the precise dates of publication of the taxonomic works of Germar's Versteinerungen (1844–1853) and Schimper & Schenk's Palaeophytologie (1879–1890) are established for the first time.

Ferns are poorly explored species from a pharmaceutical perspective compared to other terrestrial plants. In this work, the antioxidant and tyrosinase inhibitory activities of hydrophilic and lipophilic extracts, together with total polyphenol content, were evaluated in order to explore the potential cosmetic applications of four Spanish ferns collected in the Prades Mountains (Polypodium vulgare L., Asplenium adiantum-nigrum L., Asplenium trichomanes L., and Ceterach officinarum Willd). The antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, oxygen radical absorbance capacity (ORAC) and xanthine/xanthine oxidase (X/XO) assays. The potential to avoid skin hyperpigmentation was tested by inhibiting the tyrosinase enzyme, as this causes melanin synthesis in the epidermis. All ferns were confirmed as antioxidant and anti-tyrosinase agents, but interestingly hydrophilic extracts (obtained with methanol) were more potent and effective compared to lipophilic extracts (obtained with hexane). Polypodium vulgare, Asplenium adiantum-nigrum, and Ceterach officinarum methanolic extracts performed the best as antioxidants. Polypodium vulgare methanolic extract also showed the highest activity as a tyrosinase inhibitor.

The genus Thylacopteris is a small, phylogenetically isolated genus belonging to the fern family Polypodiaceae. This study describes a new species, Thylacopteris minuta , based on collections obtained during field surveys of Shan State, Myanmar. This new species is distinct from other species of Thylacopteris in its small size and presence of sclerenchyma strands in the rhizome. This species is also distinct from the only other species of Thylacopteris with molecular data available, T. papillosa , in a plastid rbcL phylogeny of Polypodiaceae. This new discovery of Thylacopteris from Myanmar suggests that this genus is still overlooked in Southeast Asia.