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Background and AimsThroughout the history of fern classification, familial and generic concepts have been highly labile. Many classifications and evolutionary schemes have been proposed during the last two centuries, reflecting different interpretations of the available evidence. Knowledge of fern structure and life histories has increased through time, providing more evidence on which to base ideas of possible relationships, and classification has changed accordingly. This paper reviews previous classifications of ferns and presents ideas on how to achieve a more stable consensus.ScopeAn historical overview is provided from the first to the most recent fern classifications, from which conclusions are drawn on past changes and future trends. The problematic concept of family in ferns is discussed, with a particular focus on how this has changed over time. The history of molecular studies and the most recent findings are also presented.Key ResultsFern classification generally shows a trend from highly artificial, based on an interpretation of a few extrinsic characters, via natural classifications derived from a multitude of intrinsic characters, towards more evolutionary circumscriptions of groups that do not in general align well with the distribution of these previously used characters. It also shows a progression from a few broad family concepts to systems that recognized many more narrowly and highly controversially circumscribed families; currently, the number of families recognized is stabilizing somewhere between these extremes. Placement of many genera was uncertain until the arrival of molecular phylogenetics, which has rapidly been improving our understanding of fern relationships. As a collective category, the so-called ‘fern allies’ (e.g. Lycopodiales, Psilotaceae, Equisetaceae) were unsurprisingly found to be polyphyletic, and the term should be abandoned. Lycopodiaceae, Selaginellaceae and Isoëtaceae form a clade (the lycopods) that is sister to all other vascular plants, whereas the whisk ferns (Psilotaceae), often included in the lycopods or believed to be associated with the first vascular plants, are sister to Ophioglossaceae and thus belong to the fern clade. The horsetails (Equisetaceae) are also members of the fern clade (sometimes inappropriately called ‘monilophytes’), but, within that clade, their placement is still uncertain. Leptosporangiate ferns are better understood, although deep relationships within this group are still unresolved. Earlier, almost all leptosporangiate ferns were placed in a single family (Polypodiaceae or Dennstaedtiaceae), but these families have been redefined to narrower more natural entities.ConclusionsConcluding this paper, a classification is presented based on our current understanding of relationships of fern and lycopod clades. Major changes in our understanding of these families are highlighted, illustrating issues of classification in relation to convergent evolution and false homologies. Problems with the current classification and groups that still need study are pointed out. A summary phylogenetic tree is also presented. A new classification in which Aspleniaceae, Cyatheaceae, Polypodiaceae and Schizaeaceae are expanded in comparison with the most recent classifications is presented, which is a modification of those proposed by Smith et al. (2006, 2008) and Christenhusz et al. (2011). These classifications are now finding a wider acceptance and use, and even though a few amendments are made based on recently published results from molecular analyses, we have aimed for a stable family and generic classification of ferns.

• Fast stomatal reactions enable plants to successfully cope with a constantly changing environment yet there is an ongoing debate on the stomatal regulation mechanisms in basal plant groups. • We measured stomatal morphological parameters in 29 fern and allied species from temperate to tropical biomes and two outgroup angiosperm species. Stomatal dynamic responses to environmental drivers were measured in 16 ferns and the two angiosperms using a gas-exchange system. Principal components analyses were used to further reveal the structure–function relationships in stomata. • We show a >10-fold variation for stomatal opening delays and 20-fold variation for stomatal closing delays in ferns. Across species, stomatal responses to vapor pressure deficit (VPD) were the fastest, while light and [CO₂] responses were slower. In most cases the outgroup species’ reaction speeds to changes in environmental variables were similar to those of ferns. • Correlations between stomatal response rate and size were apparent for stomatal opening in light and low [CO₂] while not evident for closing reactions and changes in VPD. No correlations between stomatal density and response speed were observed. Together, this study demonstrates different mechanisms controlling stomatal reactions in ferns at different environmental stimuli, which should be considered in future studies relating stomatal morphology and function.

Despite long-time awareness of the importance of the location of buds in plant biology, research on belowground bud banks has been scant. Terms such as lignotuber, xylopodium and sobole, all referring to belowground bud-bearing structures, are used inconsistently in the literature. Because soil efficiently insulates meristems from the heat of fire, concealing buds below ground provides fitness benefits in fire-prone ecosystems. Thus, in these ecosystems, there is a remarkable diversity of bud-bearing structures. There are at least six locations where belowground buds are stored: roots, root crown, rhizomes, woody burls, fleshy swellings and belowground caudexes. These support many morphologically distinct organs. Given their history and function, these organs may be divided into three groups: those that originated in the early history of plants and that currently are widespread (bud-bearing roots and root crowns); those that also originated early and have spread mainly among ferns and monocots (nonwoody rhizomes and a wide range of fleshy underground swellings); and those that originated later in history and are strictly tied to fire-prone ecosystems (woody rhizomes, lignotubers and xylopodia). Recognizing the diversity of belowground bud banks is the starting point for understanding the many evolutionary pathways available for responding to severe recurrent disturbances.

Rates of nucleotide substitution were previously shown to be several times slower in the plastid inverted repeat (IR) compared with single‐copy (SC) regions, suggesting that the IR provides enhanced copy‐correction activity. To examine the generality of this synonymous rate dependence on the IR, we compared plastomes from 69 pairs of closely related species representing 52 families of angiosperms, gymnosperms, and ferns. We explored the breadth of IR boundary shifts in land plants and demonstrate that synonymous substitution rates are, on average, 3.7 times slower in IR genes than in SC genes. In addition, genes moved from the SC into the IR exhibit lower synonymous rates consistent with other IR genes, while genes moved from the IR into the SC exhibit higher rates consistent with other SC genes. Surprisingly, however, several plastid genes from Pelargonium, Plantago, and Silene have highly accelerated synonymous rates despite their IR localization. Together, these results provide strong evidence that the duplicative nature of the IR reduces the substitution rate within this region. The anomalously fast‐evolving genes in Pelargonium, Plantago, and Silene indicate localized hypermutation, potentially induced by a higher level of error‐prone double‐strand break repair in these regions, which generates substitutional rate variation.

Premise of the Study Phylogenetic support has been difficult to evaluate within the green plant tree of life partly due to a lack of specificity between conflicted versus poorly informed branches. As data sets continue to expand in both breadth and depth, new support measures are needed that are more efficient and informative. Methods We describe the Quartet Sampling (QS) method, a quartet‐based evaluation system that synthesizes several phylogenetic and genomic analytical approaches. QS characterizes discordance in large‐sparse and genome‐wide data sets, overcoming issues of alignment sparsity and distinguishing strong conflict from weak support. We tested QS with simulations and recent plant phylogenies inferred from variously sized data sets. Key Results QS scores demonstrated convergence with increasing replicates and were not strongly affected by branch depth. Patterns of QS support from different phylogenies led to a coherent understanding of ancestral branches defining key disagreements, including the relationships of Ginkgo to cycads, magnoliids to monocots and eudicots, and mosses to liverworts. The relationships of ANA‐grade angiosperms (Amborella, Nymphaeales, Austrobaileyales), major monocot groups, bryophytes, and fern families are likely highly discordant in their evolutionary histories, rather than poorly informed. QS can also detect discordance due to introgression in phylogenomic data. Conclusions Quartet Sampling is an efficient synthesis of phylogenetic tests that offers more comprehensive and specific information on branch support than conventional measures. The QS method corroborates growing evidence that phylogenomic investigations that incorporate discordance testing are warranted when reconstructing complex evolutionary histories, in particular those surrounding ANA‐grade, monocots, and nonvascular plants.

Research summary: Research traditionally uses experiential learning arguments to explain the existence of a positive relationship between repetition of an activity and performance. We propose an additional interpretation of this relationship in the context of discrete corporate development activities. We argue that firms choose to repeat successful activities, thereby accumulating high experience with them. Data on 437 aircraft projects introduced through three governance modes show that the positive performance effect of the firm's experience with the focal mode becomes insignificant after accounting for experience endogeneity. We suggest that in a general case, experience with corporate development activities may be tinged with both learning and selection effects. Therefore, omitting to account for experience endogeneity may lead to incorrect conclusions from an \"empirically observed\" positive experience—performance relationship. Managerial summary: This paper emphasizes that firms generally choose to undertake the corporate development activities (new product introductions, diversification moves, international expansions, alliances, acquisitions, etc.) with which they have been the most successful in the past and that they expect to be the most successful in the future. Hence, if a firm possesses certain capabilities, it will repeatedly engage in certain activities corresponding to those capabilities, thereby simultaneously achieving high levels of activity experience as well as superior activity performance. This view suggests that an \"empirically observed\" positive experience—performance relationship may not be due solely to learning-based enhanced capabilities but may also be driven by astute self-selection. Overall, we provide a new interpretation of the relationship between experience and performance in the context of infrequent, heterogeneous, and causally-ambiguous corporate development activities.

This research conducted a comprehensive analysis of Washington’s strategic application of coercive diplomacy toward Beijing, focusing on three principal dimensions: political, economic, and military. Grounded in the theoretical frameworks of coercive diplomacy, the Truman Doctrine, and “Trump’s Transactional Diplomacy,” the study employed a hybrid methodology combining content and event data analysis to examine diplomatic behaviors, political statements, tariff policies, technological measures, and military maneuvers enacted by the Trump 2.0 administration. First, Washington utilized coercive measures to reaffirm its global superiority over China. Domestic self-reliance initiatives, such as the AI Action Plan, aimed to demonstrate that U.S. endogenous capabilities remained competitive with China’s manufacturing infrastructure. Second, the strategic deployment of its alliance system underscored America’s intent to assert leadership over a globally integrated network of political, economic, and defense partnerships, contrasting with China’s comparatively modest coalition. Third, coercive diplomacy extended beyond Sino-American dynamics; the Trump administration applied similar pressure tactics toward strategic partners worldwide, often leveraging economic dominance through tariff threats. Strategically, coercive diplomacy toward China appeared poised to become a long-term doctrine, as countering Beijing represented one of the few bipartisan convergences in U.S. politics. In response, China was expected to reinforce domestic resilience and alliance-building to prepare for sustained confrontation. This rivalry was likely to trigger the most extensive multidimensional competition in modern history. Developing nations must adopt proactive, neutral diplomacy to strengthen internal capacities, while they should avoid positioning themselves as adversaries to either superpower.

Disabled people/people with disabilities (DP/PWDs) need allies in general and subject matter specific allies in particular given the many problems they face in their daily lives, as it is, for example, evident in the language of the UN Convention on the Rights of Persons with Disabilities. Numerous actions are required from allies of, for example, DP/PWDs and other marginalized groups. Authentic allies are often expected to take on activist roles, yet activism carries the risk of activist burnout, which in turn places allies at risk of ally burnout. Despite this, ally burnout is rarely discussed in the literature, and, to date, there are no studies that specifically examined ally burnout in the context of allyship to and by DP/PWDs. The aim of this study was to deepen our understanding of the factors and topics that heighten the risk of ally burnout, including both non-disabled individuals acting as allies to DP/PWDs and DP/PWDs acting as allies to others. In this study, our participants included eighty-seven critical disability studies students. Critical disability studies students were chosen because they see themselves as allies of DP/PWDs and want to make a positive difference in the lives of DP/PWDs, including disabled students. We used an online survey using the Qualtrics platform as our tool to obtain the data. Our participants identified many factors that can lead to ally burnout and indicated many actions needed to decrease the danger of ally burnout of non-disabled people being allies of DP/PWDs and DP/PWDs being allies of others.

1. Since the early colonization of land, plants depend, to various extents, on mycorrhizal fungi to meet their nutrient demands. In most mycorrhizal symbioses, plants provide sugars derived from photosynthesis to the fungi, whereas the fungi provide essential minerals to the plant. However, in some plants, the flow of carbon has reversed and the fungi provide carbon to the plants. These plants are called mycoheterotrophs. However, it remains unclear how and under which circumstances trophic modes change and whether transitions in trophic modes are associated with changes in mycorrhizal communities. 2. Here, we review the available literature on mycorrhizal associations and trophic modes in plants. We first outline how trophic modes can be determined and how they differ across plants. We then investigate the evolutionary context under which mycoheterotrophy originated. We also examine the mycorrhizal communities associating with autotrophic, partially mycoheterotrophic and fully mycoheterotrophic plants within different plant families and investigate whether commonalities can be observed. 3. Our overview shows that mycoheterotrophy has originated more than 40 times through evolutionary time and can be found in a wide range of plant groups, including liverworts, lycophytes, ferns, monocots and dicots. Partial mycoheterotrophy appears to be much more common than previously anticipated and represents an almost continuous gradient between autotrophy and full mycoheterotrophy. 4. Comparison of the mycorrhizal communities associating with autotrophic, partial and full mycoheterotrophic plants indicates that, although they share some commonalities, shifts from autotrophy to full mycoheterotrophy are accompanied by either losses or shifts in mycorrhizal partners, suggesting that full or partial loss of photosynthesis selects for different mycorrhizal communities. 5. Synthesis. Partial mycoheterotrophy appears to be much more common than previously thought and represents an almost continuous gradient from autotrophy to full mycoheterotrophy. Evolution to full mycoheterotrophy is challenging as it requires specific adaptations and often a switch to other mycorrhizal partners. More detailed analyses of the functionality of different mycorrhizal systems co-occurring in the roots of a single plant and the costs of mycorrhizal switching are needed to understand the precise mechanisms leading to full mycoheterotrophy.

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.