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The central problem in biogeography is that interactions between different processes result in the formation of historical patterns, such that it is difficult to discriminate the relative roles of vicariance and dispersal. Ferns are distributed by small wind-dispersed propagules that are produced in very large numbers and capable of dispersing thousands of kilometers. Thus, most taxon distributions in ferns are assumed to be a function of dispersal rather than vicariance. Here, we review some case examples that provide good evidence for vicariance and dispersal in ferns. We then ask whether dispersal is so extensive in ferns that vicariance is no longer detectable in most cases. Although we think that too few studies have been carried out to make generalizations at this stage, we outline the criteria for an effective research programme that can address this issue. Phylogenetic and distributional data are needed, not only because they are lacking in an evolutionarily important group of organisms, but also because data from ferns and other cryptogams are likely to be crucial in making broad biogeographic statements.
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... Pteridophytes, including lycophytes and monilophytes, are organisms with high dispersive capacity [39], by spores, which favors population connectivity and decreased genetic structure [40]. This may account for its low levels of endemism by comparison with angiosperms, as occur in Macaronesia. ...
... In ferns, the reproductive system is closely related to the colonizing capacity of the species. The colonization of new habitats will be more likely for those species with intragametophytic selfing, which are able to establish a new population even from just one spore [39,44]. In herbaceous plants with clonal reproduction, after an initial founder event by one or few genotypes, the expansion process can occur via vegetative reproduction (e.g., [102,103]). ...
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Macaronesia has been considered a refuge region of the formerly widespread subtropical lauroid flora that lived in Southern Europe during the Tertiary. The study of relict angiosperms has shown that Macaronesian relict taxa preserve genetic variation and revealed general patterns of colonization and dispersal. However, information on the conservation of genetic diversity and range dynamics rapidly diminishes when referring to pteridophytes, despite their dominance of the herbaceous stratum in the European tropical palaeoflora. Here we aim to elucidate the pattern of genetic diversity and phylogeography of Diplazium caudatum, a hypothesized species of the Tertiary Palaeotropical flora and currently with its populations restricted across Macaronesia and disjunctly in the Sierras de Algeciras (Andalusia, southern Iberian Peninsula). We analysed 12 populations across the species range using eight microsatellite loci, sequences of a region of plastid DNA, and carry out species-distribution modelling analyses. Our dating results confirm the Tertiary origin of this species. The Macaronesian archipelagos served as a refuge during at least the Quaternary glacial cycles, where populations of D. caudatum preserved higher levels of genetic variation than mainland populations. Our data suggest the disappearance of the species in the continent and the subsequent recolonization from Macaronesia. The results of the AMOVA analysis and the indices of clonal diversity and linkage disequilibrium suggest that D. caudatum is a species in which inter-gametophytic outcrossing predominates, and that in the Andalusian populations there was a shift in mating system toward increased inbreeding and/or clonality. The model that best explains the genetic diversity distribution pattern observed in Macaronesia is, the initial and recurrent colonization between islands and archipelagos and the relatively recent diversification of restricted area lineages, probably due to the decrease of favorable habitats and competition with lineages previously established. This study extends to ferns the concept of Macaronesia archipelagos as refugia for genetic variation.
... However, in particular, large invasive spiders, such as Dysderacrocata, use human-mediated transfer (Nedvěd et al. 2011), which may help increase the IRR of these species. Similar to angiosperms and vertebrates (except for birds), the successful expansion of pteridophytes worldwide is likely due to their high dispersal ability (linked to ferns producing numerous small spores that are easily transported over long distances and remain viable for several years ;Tryon 1970;Smith 1972;Wolf et al. 2001), while plants, in general, expand in great part because of horticulture, aquaculture (Reichard and White 2001) and aquarium trade (Peres et al. 2018). ...
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Humans are facilitating the introduction and range expansion of invasive alien species (IAS), which have negatively impacted ecological and socio-economic systems worldwide. Understanding the global diffusion of IAS is important for developing environmental policies and management strategies. We estimate the rate of increase and the doubling times of the number of new records of 178 IAS using a global dataset with c. 3.4 million records obtained over c. 100 years. Here, we show that the number of records of IAS have exponentially increased with a mean double time of c. 14 years across the Earth. For the most analysed species, the number of records increased faster in the non-native than native continents, suggesting that such IAS might be exponentially expanding their range size. We also found that each continent has a taxonomic group with a particular increase in IAS records. Governments and scientists should pay attention to these taxonomic groups to implement appropriate control or management actions. Our study provides an indication that the current local, regional and continental efforts to control invasions may be not sufficient at the global scale. This is a concerning situation given the great number of areas available for invasion worldwide.
... Pteridophytes, including both lycophytes and ferns, are considered to be good climate indicators (Khine et al., 2019) because they are dispersed by spores which can travel thousands of kilometers by wind (Wolf et al., 2001), so that their distributions are more in equilibrium with climate than distributions of seed plants (Qian, 2009), and because the stomatal control of pteridophytes is less efficient than that of angiosperms (Brodribb & McAdam, 2011), so that they appear to be more susceptible to limited water availability . Across latitudinal gradients, species richness of pteridophytes generally decreases polewards (Karger et al., 2011), whereas on elevational gradients, species richness of pteridophytes commonly peaks at mid-elevations (Bhattarai et al., 2004;Khine et al., 2019;Tanaka & Sato, 2013;Tang et al., 2014). ...
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There is a consensus that climate factors strongly influence species richness along elevation gradients, but which factors are crucial and how they operate are still elusive. Here, we assess the relative importance of temperature‐related versus precipitation‐related variables and the relative importance of extreme climate versus climate seasonality in driving pteridophyte species richness. We used correlation and regression analyses to relate species richness of pteridophytes, and their two major groups (lycophytes, ferns), in fifty 100‐m vertical bands to climatic factors representing different aspects of climatic conditions (general climate, stressful climate, and climate seasonality). Variation partitioning analysis was used to determine the relative importance of each group of climatic factors on species richness. Across the entire elevational gradient, species richness had a parabolic response to mean annual temperature (adjusted R2 = .87−.91), and a linear response to annual precipitation (adjusted R2 = .82). Mean annual temperature and annual precipitation in the second‐order polynomial model together explained 96.3%−98.7% of the variation in species richness. The variation in species richness uniquely explained by minimum temperature of the coldest month was much greater than that uniquely explained by temperature seasonality, but the variation in species richness uniquely explained by precipitation during the driest month was much smaller than that uniquely explained by precipitation seasonality. Overall, extreme climate variables explained slightly more variation than did climate seasonality. Our study suggests that pteridophyte richness along the elevational gradient is largely driven by a combination of both temperature‐ and precipitation‐related parameters, although precipitation‐related variables play a slightly stronger role, and that extreme low temperature events (at high elevations) and seasonal precipitation variability (at low elevations) are the strongest determinants of pteridophyte species richness. Relationships between elevation and species richness (a) or species density (b) for pteridophytes in Nepal. Each dot represents a 100‐m elevation band. Species density is defined as species richness in an elevational band being divided by the log10‐tranformed area (km2) of the elevational band.
... Given the prevalence of reproduction through spores, ferns in particular tend to be excellent dispersers and therefore are often believed to be more likely to occur whenever there are suitable conditions for their establishment and growth (although this notion has yet to be tested experimentally, Wild and Gagnon 2005). For instance, dispersal by wind in ferns and lycophytes can vary greatly between taxa but many species are known to have remarkable long-distance dispersal abilities (Barrington 1993;Wolf et al. 2001) and thus are often able to overcome geographical barriers more easily than other taxonomic groups (Tyron 1970). However, our understanding of how fern and lycophyte lineages evolved to occupy their current climatic niches is still incipient (Bystriakova et al. 2011;Hernandez-Rojas et al. 2021). ...
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Honduran fern and lycophyte taxa under present and future climates. We found that species were distributed throughout most of the available climatic space. Under RCP2.6 and RCP8.5 projections 128 to 391 species will have their average niche positions outside of the predicted available climatic space by the years 2049-2099. Particularly affected will be species that grow in low temperature and high precipitation areas, which represent high altitude parks, such as Celaque National Park. Epiphytes showed smaller variance in their climatic niches than terrestrial species. However, terrestrial species showed higher loss in climate space (e.g., 82.9% vs. 17.1% for RCP8.5) and are more likely to be at risk in the future. In general, Hondu-ras is expected to become drier, with more extreme events of severe drought. Considering that ferns are particularly sensitive to changes in climate, if tested in the future, they could be used as a proxy for other Honduran plant taxa.
... In the aftermath of a fire event, most species die out and recolonization mediated by propagules from the surrounding landscape may be stochastic (Hubbell, 2001). Ferns can quickly colonize areas after extreme disturbance events such as fires, landslides, hurricanes and deforestation (Walker & Sharpe, 2010 and references therein) because of the high wind-dispersal capacity of its propagules, known as spores, which are both highly abundant and longlived (Perrie & Brownsey, 2007;Wolf et al., 2001). ...
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Tropical forests have been rapidly deforested and degradation worldwide has outpaced biodiversity field sampling. No study to date has assessed the effects of insular habitats induced by hydroelectric dams on Amazonian understory plants. Fern community responses to anthropogenic effects on tropical forest islands can be revealed at a faster pace by using simple and cheap, yet informative, protocols that could be applied by non‐specialists. This study seeks to both understand the drivers of fern and lycophytes assemblages on forest islands and investigate the relative costs and effectiveness of a simplified sampling protocol that can be applied by non‐specialists. Fern species were sampled by a non‐specialist who photographed all ferns and lycophytes within seventeen 0.25‐ha plots on 10 forest islands at the lake of Balbina Hydroelectric dam, central Amazonia. Sampling was carried out opportunistically during a field expedition planned to conduct tree inventories. As predictors, we used locally measured or GIS‐derived descriptors of plot and landscape conditions. We used multivariate and linear models to further assess the influence of predictors on patterns of species richness and composition of ferns assemblages. A total of 286 photographed individual ferns or lycophytes represented at least 23 species and 14 genera. The average number of taxa per plot was 6.1 in the islands and 14.3 in the mainland. The species pool found on islands was a nested subset of the mainland fern community. Species richness was positively related to island size and negatively related to isolation and fire severity. Area, isolation and fire severity also significantly explained variation in community composition. The relative cost of the picture‐based fern protocol applied was very modest (only 4% of the total expedition budget), even compared to the typically low cost of alternative field campaigns. We conclude that fern community structure in this forest archipelago was primarily driven by island size, isolation and fire disturbance. Moreover, we show that a simple sampling protocol carried out by a non‐specialist can lead to inexpensive and highly reliable ecological data. This opens an avenue for crowdsourcing ecological fern data collections using a citizen science approach. Tropical forests have been rapidly deforested and degradation worldwide has outpaced biodiversity field sampling. No study to date has assessed the effects of insular habitats induced by hydroelectric dams on Amazonian understory plants. Fern community responses to anthropogenic effects on tropical forest islands can be revealed at a faster pace by using simple and cheap, yet informative, protocols that could be applied by non‐specialists. This study seeks to both understand the drivers of fern and lycophytes assemblages on forest islands and investigate the relative costs and effectiveness of a simplified sampling protocol that can be applied by non‐specialists. Fern species were sampled by a non‐specialist who photographed all ferns and lycophytes within seventeen 0.25‐ha plots on 10 forest islands at the lake of Balbina Hydroelectric dam, central Amazonia. Sampling was carried out opportunistically during a field expedition planned to conduct tree inventories. As predictors, we used locally measured or GIS‐derived descriptors of plot and landscape conditions. We used multivariate and linear models to further assess the influence of predictors on patterns of species richness and composition of ferns assemblages. A total of 286 photographed individual ferns or lycophytes represented at least 23 species and 14 genera. The average number of taxa per plot was 6.1 in the islands and 14.3 in the mainland. The species pool found on islands was a nested subset of the mainland fern community. Species richness was positively related to island size and negatively related to isolation and fire severity. Area, isolation and fire severity also significantly explained variation in community composition. The relative cost of the picture‐based fern protocol applied was very modest (only 4% of the total expedition budget), even compared to the typically low cost of alternative field campaigns. We conclude that fern community structure in this forest archipelago was primarily driven by island size, isolation and fire disturbance. Moreover, we show that a simple sampling protocol carried out by a non‐specialist can lead to inexpensive and highly reliable ecological data. This opens an avenue for crowdsourcing ecological fern data collections using a citizen science approach. As florestas tropicais estão sendo desmatadas rapidamente e a degradação em todo o mundo ocorre de forma mais rápida que coletas de dados em campo sobre a biodiversidade. Por exemplo, nenhum estudo até o momento avaliou os efeitos de habitats insulares induzidos por barragens hidrelétricas em plantas de sub‐bosque da Amazônia. As respostas da comunidade de samambaias aos efeitos antrópicos em ilhas de floresta tropical podem ser reveladas em um ritmo mais rápido usando protocolos simples, baratos, e ainda assim informativos. Tais protocolos podem ser aplicados por não especialistas acelerando, portanto, o nosso entendimento sobre como a diversidade de espécies é moldado em paisagens altamente fragmentadas. Este estudo busca compreender os fatores determinantes de variações nas assembléias de samambaias e licófitas em ilhas florestais e investigar os custos relativos vs. eficácia de um protocolo de amostragem simplificado que pode ser aplicado por não especialistas e, portanto, tem potencial para ser usado em estratégias de coleta de dados ecológicos de forma coletiva (crowdsourcing). As espécies de samambaias foram amostradas por um não especialista que fotografou todas as samambaias e licófitas em 17 parcelas de 0,25 ha em 10 ilhas florestais no lago da Barragem Hidrelétrica de Balbina, na Amazônia central. A amostragem foi realizada de forma oportunista, durante uma expedição de campo planejada para realizar um inventário de árvores em parcelas permanentes. Para cada uma das parcelas amostradas, usamos um conjunto de variáveis preditoras medidas localmente ou derivados de SIG nas escalas da parcela, do fragmento florestal ou da paisagem. Usamos Análise de Coordenadas Principais (PCoA) e Modelos Lineares Mistos Generalizados (GLMMs) para avaliar os fatores determinantes dos padrões de variação na composição e riqueza de espécies de samambaias. Um total de 286 indivíduos de samambaias ou licófitas foram fotografados, representanto pelo menos 23 espécies e 14 gêneros. Em media, foram observadas 6,1 espécies nas ilhas e 14,3 no continente. As espécies encontradas nas ilhas representaram um subconjunto da comunidade de samambaias do continente. A riqueza de espécies foi maior quanto maior e mais próxima do continente era a ilha. A riqueza diminuiu quanto maior a severidade do fogo nas ilhas. Área, isolamento e severidade do fogo também explicaram significativamente a variação na composição da comunidade. O custo relativo do protocolo de samambaias baseado em imagens aplicado por um não especialista foi modesto (em nosso caso, apenas 4% do orçamento total da expedição), mesmo em comparação ao custo tipicamente baixo de muitas campanhas de campo. Concluimos que estrutura da comunidade de samambaias neste arquipélago florestal foi impulsionada principalmente pelo tamanho da ilha, isolamento e incêndio. Além disso, demonstramos que um protocolo de amostragem simples, realizado por um não especialista pode levar a dados ecológicos baratos e altamente informativos. Isso abre um caminho para coletas de dados de samambaias ecológicas usando uma abordagem de ciência‐cidadã. As florestas tropicais estão sendo desmatadas rapidamente e a degradação em todo o mundo ocorre de forma mais rápida que coletas de dados em campo sobre a biodiversidade. Por exemplo, nenhum estudo até o momento avaliou os efeitos de habitats insulares induzidos por barragens hidrelétricas em plantas de sub‐bosque da Amazônia. As respostas da comunidade de samambaias aos efeitos antrópicos em ilhas de floresta tropical podem ser reveladas em um ritmo mais rápido usando protocolos simples, baratos, e ainda assim informativos. Tais protocolos podem ser aplicados por não especialistas acelerando, portanto, o nosso entendimento sobre como a diversidade de espécies é moldado em paisagens altamente fragmentadas. Este estudo busca compreender os fatores determinantes de variações nas assembléias de samambaias e licófitas em ilhas florestais e investigar os custos relativos vs. eficácia de um protocolo de amostragem simplificado que pode ser aplicado por não especialistas e, portanto, tem potencial para ser usado em estratégias de coleta de dados ecológicos de forma coletiva (crowdsourcing). As espécies de samambaias foram amostradas por um não especialista que fotografou todas as samambaias e licófitas em 17 parcelas de 0,25 ha em 10 ilhas florestais no lago da Barragem Hidrelétrica de Balbina, na Amazônia central. A amostragem foi realizada de forma oportunista, durante uma expedição de campo planejada para realizar um inventário de árvores em parcelas permanentes. Para cada uma das parcelas amostradas, usamos um conjunto de variáveis preditoras medidas localmente ou derivados de SIG nas escalas da parcela, do fragmento florestal ou da paisagem. Usamos Análise de Coordenadas Principais (PCoA) e Modelos Lineares Mistos Generalizados (GLMMs) para avaliar os fatores determinantes dos padrões de variação na composição e riqueza de espécies de samambaias. Um total de 286 indivíduos de samambaias ou licófitas foram fotografados, representanto pelo menos 23 espécies e 14 gêneros. Em media, foram observadas 6,1 espécies nas ilhas e 14,3 no continente. As espécies encontradas nas ilhas representaram um subconjunto da comunidade de samambaias do continente. A riqueza de espécies foi maior quanto maior e mais próxima do continente era a ilha. A riqueza diminuiu quanto maior a severidade do fogo nas ilhas. Área, isolamento e severidade do fogo também explicaram significativamente a variação na composição da comunidade. O custo relativo do protocolo de samambaias baseado em imagens aplicado por um não especialista foi modesto (em nosso caso, apenas 4% do orçamento total da expedição), mesmo em comparação ao custo tipicamente baixo de muitas campanhas de campo. Concluimos que estrutura da comunidade de samambaias neste arquipélago florestal foi impulsionada principalmente pelo tamanho da ilha, isolamento e incêndio. Além disso, demonstramos que um protocolo de amostragem simples, realizado por um não especialista pode levar a dados ecológicos baratos e altamente informativos. Isso abre um caminho para coletas de dados de samambaias ecológicas usando uma abordagem de ciência‐cidadã. Tropical forests have been rapidly deforested and degradation worldwide has outpaced biodiversity field sampling. We here show that a simple sampling protocol carried out by a non‐specialist can lead to inexpensive and highly reliable ecological data. Moreover, we disentangle the effects of local and landscape characteristics in fern community structure in a human‐made forest archipelago in central Amazonia.
... Ferns, which include about 12,000 species worldwide (Hassler, 2004e2021), are one of the oldest and the most species-rich groups of vascular plants (Mabberley, 2008;Qian et al., 2021a). Fern propagules are spores, which are small (usually <0.1 mm in equatorial axis and polar axis; Adsersen, 1995), and are capable of dispersing thousands of kilometers by wind (Wolf et al., 2001). Ferns are generally distributed broadly, and fern distributions are thought to be more in equilibrium with climate than most other groups of vascular plants (Qian, 2009). ...
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Despite that several studies have shown that data derived from species lists generated from distribution occurrence records in the Global Biodiversity Information Facility (GBIF) are not appropriate for those ecological and biogeographic studies that require high sampling completeness, because species lists derived from GBIF are generally very incomplete, Suissa et al. (2021) generated fern species lists based on data with GBIF for 100 km × 100 km grid cells across the world, and used the data to determine fern diversity hotspots and species richness−climate relationships. We conduct an evaluation on the completeness of fern species lists derived from GBIF at the grid-cell scale and at a larger spatial scale, and determine whether fern data derived from GBIF are appropriate for studies on the relations of species composition and richness with climatic variables. We show that species sampling completeness of GBIF is low (<40%) for most of the grid cells examined, and such low sampling completeness can substantially bias the investigation of geographic and ecological patterns of species diversity and the identification of diversity hotspots. We conclude that fern species lists derived from GBIF are generally very incomplete across a wide range of spatial scales, and are not appropriate for studies that require data derived from species lists in high completeness. We present a map showing global patterns of fern species diversity based on complete or nearly complete regional fern species lists.
... Such old vicariance events are often invoked to explain disjunct amphi-oceanic distributions but actually rarely demonstrated in free-sporing tracheophytes (traditional 'pteridophytes') because of their high longdistance dispersal (LDD) ability due to their minute, numerous and light spores. In many recent studies, LDD seems to explain the majority of the disjunct and wide distributions in leptosporangiate ferns (as reviewed by Wolf, Schneider & Ranker, 2001;Haufler, 2007;Schaefer, 2011 (Labiak et al., 2014), Polystichum Roth (Le Péchon et al., 2016), Ctenitis (C.Chr.) C.Chr. , Rumohra Raddi (Bauret et al., 2017a) and grammitids (Bauret et al., 2017b). ...
Article
The filmy fern genus Trichomanes mainly comprises Neotropical species and a few taxa in Africa and the western Indian Ocean. The aim of this study is to infer the phylogenetic placement of all five Afro-Malagasy taxa in the genus and to investigate their history via an expanded and dated phylogenetic analysis including 39 species representing over half the diversity of the genus. The results support the monophyly of Trichomanes including all the sampled species attributed to the genus, but also suggest the inclusion of the species Abrodictyum cellulosum, revealing a morphological diversity of the genus greater than what was traditionally recognized, and highlighting the importance of the campanulate sorus as a generic diagnostic character. To accommodate those new phylogenetic results and morphological investigations, we describe a new subgenus Afrotrichomanes grouping the Afro-Malagasy taxa (except T. crenatum). The dated history of the genus among the trichomanoids suggests at least two origins for the Palaeotropical species. A recent Cainozoic colonization from the Neotropics towards Africa gave rise to the West African taxon T. crenatum, and a possible Mesozoic vicariance event gave rise to subgenus Afrotrichomanes. The low species diversity of the genus in the Afro-Malagasy region is discussed.
... Many life-history traits of ferns, such as their unique life cycles with independent, often ephemeral gametophytes and relatively long-lived sporophytes, make it difficult to study one or more of these processes, such as mutation and selection, in these organisms. However, other traits, such as their ability to produce massive quantities of easily wind-dispersed spores (Wolf et al. 2001), make ferns ideal candidates for studying other processes, such as gene flow. ...
Article
The Amotape-Huancabamba Zone, straddling the Huancabamba Depression in the tropical Andes, is often recognized as a major hotspot of species richness for plants and animals in the Neotropics. The biogeographic role of the area as a barrier, transition, or unique endemism zone in the Andes has long been debated. Here, using tree ferns, we take a new look at this question and discuss the biogeographic significance and limits of the Amotape-Huancabamba Zone. We find that tree fern distribution supports the idea that the Amotape-Huancabamba zone is a unique biogeographic unit within the Andes defined by high endemism, overlap of the floras of the Northern and Central Andes, and high overall species richness; however, the centrally located Huancabamba-Marañón depression plays only a minor role as a floristic barrier.
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Background Despite the broad distribution of several species in Gleicheniaceae in the neotropical region, Diplopterygium is the only genus having a restricted distribution. Species of Gleicheniaceae occupy open (including anthropogenic) habitats and produce large amounts of wind-dispersed propagules – so why does Diplopterygium bancroftii, the only neotropical species in the genus, have a restricted distribution? Aims We investigated if the restricted distribution of Diplopterygium in the Neotropics reflected the absence of suitable areas for the establishment. Methods We used species distribution modeling to identify suitability areas during different periods of the Pleistocene (Last Glacial Maximum and Last Interglacial), the Holocene, and the present. Results The environmental suitability model at the present time corroborated the current distribution of D. bancroftii, and also evidenced additional suitable potential areas where the species has so far not been recorded, especially in eastern Brazil. In projections of the past, no connectivity was observed between suitable areas in the Andes and eastern Brazil. Conclusions As neither the dispersal ability nor the absence of suitable areas at the present time or in the past were limiting factors to the range expansion of Diplopterygium, we discuss possible migration barriers and propose a hypothesis for its colonization history in the Neotropics.
Conference Paper
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The taxonomic status of certain Pteridium (bracken) populations in Britain and their relationships with other British populations and with North American taxa, are much disputed. Apart from the common Pteridium aquilinum subsp. aquilinum var. aquilinum these other British populations have been variously treated as as either subsp. latiusculum (Tryon's var. latiusculum), as a separate species P. pinetorum, or as hybrids between British var. aquilinum and North American latiusculum. In an attempt to infer evolutionary relationships among these taxa, we sequenced several regions of the chloroplast genome, including the genes rbcL, atpB, and rps4, in addition to the spacer regions between rbcL and atpB, and between atpB and atpE. We sampled from specimens representing six bracken taxa and seven populations from both Britain and North America. Specimens from Britain were chosen from aquilinum, fulvum, and pinetorum. North American taxa were represented by latiusculum (2 populations), pseudocaudatum, and pubescens. Following alignment, sequences were subjected to phylogenetic analysis.
Article
The extreme isolation and mid-Pacific origin of the Hawaiian archipelago has ensured that all indigenous organisms have arrived via long-distance dispersal or have evolved from successfully colonizing species. Although this isolation has also produced high rates of species endemism in angiosperms (89% or more), that rate in pteridophytes is considerably less (76%). The ratio of native species to the estimated number of original successful colonizing species in angiosperms (3.4) is more than double that for pteridophytes (1.6). One possible explanation for the lower speciation rate in pteridophytes is that populations of these species are more likely to experience interpopulational gene flow because of the great vagility of their wind-dispersed spores. We conducted isozymic surveys of populations from the island of Hawaii of the indigenous allotetraploid species Asplenium adiantum-nigrum, putatively derived from two strictly European diploid taxa. Our data support multiple hybrid origins for the populations surveyed, with a minimum of 3, and possibly as many as 17, discrete hybridization events having produced the genetic diversity observed. Since the parental taxa are not found in Hawaii, each hybrid lineage must have arrived in the archipelago independently of the others. Similar long-distance, repeated dispersal events may be occurring between insular and noninsular populations of other native pteridophytes in Hawaii and in other insular regions of the world, thus contributing to the relatively low rates of speciation and insular endemism in this ancient group of plants.
Chapter
A largely tropical family of six mostly epiphytic genera that are restricted either to the New World or the Old World, except for Antrophyum and Vittaria, which are widely distributed in both regions. The spores are mostly trilete but are either tri- or monolete in Vittaria and Antrophyum. The sporoderm consists of a blechnoid type of exospore and a thin perispore of one or two layers, usually plain or papillate with globules or rodlets.