Spore viability is a key parameter of reproduction and population dynamics in spore-producing plants. In ferns, spore abortion is commonly assessed by morphology, germination tests or staining, but these methods are unreliable in lycophytes due to high morphological variability, failure of germination tests and thick sporopollenin walls, which limit dye permeability. Using central European cytotypes of Huperzia selago as a model, we evaluated whether a visually-based spore abortion index (SAI; optical microscopy) reflects biochemical indicators of viability. SAI values were compared with bulk biochemical estimates of protein, nucleic acid and sporopollenin (by Fourier-transform infrared spectroscopy, FTIR) and oil content (gravimetrically). All biochemical indicators were significantly correlated with SAI, confirming that visual classification reliably reflects spore viability. Viable spores contained well-developed protoplasts with visible oil droplets, whereas aborted spores lacked cytoplasmic content and appeared irregular and darker, often containing air pockets. Oil concentration strongly correlated with relative protein and nucleic acid content and was negatively correlated with sporopollenin abundance. Spore viability also varied with ploidy level. Even cytotypes (4x, 6x) showed moderate abortion rates (1–38

Ferns and angiosperms represent the two largest vascular plant lineages but exhibit striking genomic and ecological contrasts. We investigated whether differences in genome size, chromosome architecture, GC content, and stomatal traits reveal divergent evolutionary trajectories between these lineages. We assembled the most comprehensive dataset to date, integrating genome size, chromosome number and size, GC content, and stomatal traits for over 1100 fern species and compared it with an extensive angiosperm dataset. Ferns exhibited markedly lower variability and c. 16-fold slower rates of chromosome size evolution than angiosperms. A persistent positive relationship between genome size and chromosome number in ferns suggests limited cytological post-polyploid diploidization. While ferns generally possess larger stomata, this difference disappears after accounting for genome size, indicating that nucleotypic constraints, rather than lineage-specific physiology, dictate stomatal dimensions. Both groups share a unimodal GC-genome size relationship peaking at c. 14 Gbp. Larger fern chromosomes imply lower genome-wide recombination rates, potentially limiting genetic reshuffling and adaptive potential. Our results highlight fundamentally divergent evolutionary trajectories, likely shaped by meiotic symmetry in ferns and meiotic asymmetry, possibly centromere drive, and post-polyploid diploidization in angiosperms, defining the functional and genomic landscapes of these lineages across deep evolutionary timescales.

A new fern species, Polystichum caucasicum sp. nov., is described from the Caucasus region and adjacent areas of Georgia, Armenia, Turkey and Russia. The species was likely overlooked due to its morphological similarity to P. braunii and P. aculeatum, but it can be distinguished by a combination of characters, including a densely scaly rachis, enlarged basal acroscopic pinnules, and long-pointed pinnae. P. caucasicum could also be misidentified as P. kadyrovii in this region; however, a revision of the type material confirms that P. kadyrovii is conspecific with P. aculeatum and therefore not related to the newly described taxon. Genome size analyses (flow cytometry) of 20 individuals revealed an average 2C genome size of 44.7 pg, indicating a hexaploid cytotype, which is also supported by guard cell size measurements. In addition, a comprehensive comparative analysis of genome size characteristics was conducted across the majority of European and Caucasian Polystichum species, providing estimates of genome size, monoploid genome size (1Cx), and genomic GC content. The species produces well-developed fertile spores. Polystichum caucasicum appears to be an endemic of the Caucasus region and adjacent areas, growing in a wide ecological range in humus-rich and rocky beech, ravine or alluvial forests dominated by Acer, Fagus, Tilia and Alnus. Its habitat preferences are documented through four phytosociological relev & eacute;s and realized climatic niche of the species at known locations was performed using the Chelsa Bioclim dataset.

The distribution of cytotypes and their contact zones provides insights into the spatial, morphological, and ecological differentiation of individual lineages, as well as their rates of reproductive isolation, gene flow, and/or selection. In this study, we focused on the Pulmonaria officinalis group, which comprises two widely distributed and morphologically similar species, P. obscura and P. officinalis, that differ in chromosome number. Intermediate plants, often of questionable identity, are rarely reported from mixed populations. In addition, several ornamental cultivars exhibit morphological similarities to P. officinalis. We employed flow cytometric relative genome size estimation, chromosome counting, morphometric analysis, and pollen staining methods to evaluate cytotype distribution, morphological variation, and to confirm the hybrid origin of intermediate plants and their frequency. We identified two main cytotypes, each associated with specific taxa, i.e. P. obscura (2n = 2x = 14), predominant in the northern regions, and P. officinalis s. str. (2n = 2x = 16), more common in southern areas of Central Europe. We also occasionally detected DNA-triploids in natural populations of both taxa and confirmed an intermediate cytotype (2n = 15), mainly in mixed populations of P. obscura and P. officinalis in natural contact zone, although such populations were rare. The intermediate cytotype displayed differences in relative genome size and chromosome number, as well as several morphological characters (e.g. calyx length and calyx indumentum) compared to the parental taxa. These plants also have lower fertility, with pollen viability ranging from 2 to 33

PREMISE:Apomixis in ferns is relatively common and obligatory. Sterile hybrids may restore fertility via apomixis at a cost of long-term genetic stagnation. In this study, we outlined apomixis as a possible temporary phase leading to sexuality and analyzed factors relating to transitioning to and away from apomixis, such as unreduced and reduced spore formation in apomict and apo-sex hybrid ferns. METHODS:We analyzed the genome size of 15 fern species or hybrids ("taxa") via flow cytometry. The number of reduced and unreduced gametophytes was established as a proxy for viable spore formation of either type. We also calculated the spore abortion ratio (sign of reduced spores) in several taxa, including the apo-sex hybrid Dryopteris × critica and its 16 apomictically formed offspring. RESULTS:Four of 15 sampled taxa yielded offspring variable in genome size. Specifically, each variable taxon formed one viable reduced plant among 12-451 sampled gametophytes per taxon. Thus, haploid spore formation in the studied apomicts was very rare but possible. Spore abortion analyses indicated gradually decreasing abortion (haploid spore formation) over time. In Dryopteris × critica, abortion decreased from 93.8% to mean 89.5% in one generation. CONCLUSIONS:Our results support apomixis as a transitionary phase toward sexuality. Newly formed apomicts hybridize with sexual relatives and continue to form haploid spores early on. Thus, they may get the genomic content necessary for regular meiosis and restore sexuality. If the missing relative goes extinct, the lineage gets locked into apomixis as may be the case with the Dryopteris affinis complex.

The fundamental value of universal nomenclatural systems in biology is that they enable unambiguous scientific communication. However, the stability of these systems is threatened by recent discussions asking for a fairer nomenclature, raising the possibility of bulk revision processes for "inappropriate" names. It is evident that such proposals come from very deep feelings, but we show how they can irreparably damage the foundation of biological communication and, in turn, the sciences that depend on it. There are four essential consequences of objective codes of nomenclature: universality, stability, neutrality, and transculturality. These codes provide fair and impartial guides to the principles governing biological nomenclature and allow unambiguous universal communication in biology. Accordingly, no subjective proposals should be allowed to undermine them.

Polyploidization is pivotal in plant speciation, affecting adaptability, ecological tolerance and specific geographical distribution patterns. While cytotype diversity has been extensively studied in angiosperms and ferns, knowledge in homosporous lycophytes remains very limited. Our study addresses this gap, focusing on the homosporous lycophyte Huperzia selago in Central Europe. The genome size of 1330 individuals from 208 populations were assessed via flow cytometry, revealing five distinct cytotypes (2x, 3x, 4x, 5x, 6x). Challenging chromosome counting using gemmae roots yielded average counts of 140 (2x), 204 (3x), and 262 (4x) chromosomes. The hexaploid genome size (29 pg) approached the upper limits reported for lycophytes. Tetraploids were the most abundant (72.7%), while triploids (21.3%) were less common, while the remaining cytotypes comprised less than 5% of the dataset. Geographical separation of cytotypes was not observed. However, uncommon cytotypes were associated with the Alps and triploids also occured in the highest parts of Western Carpathians. Around 27.3% of populations exhibited multiple cytotypes. Except for atypical diploids, spore abortion differed between even (21.8%) and odd ploidies (65.2%). Microcharacter (stoma, spore) proportions did not linearly correspond with increasing ploidy levels. The high ploidy-level diversity and cytotype coexistence in Central European H. selago match the well documented patterns in ferns and angiosperms. These findings provide valuable insights into lycophyte polyploidy, underscoring the necessity for broader geographical sampling and application of molecular studies to elucidate phylogenetic relationships and taxonomic classifications within the genus Huperzia.

(2957) Dryopteris affinis (Lowe) Fraser-Jenk. in Fern Gaz. 12: 56. Aug 1979 (Nephrodium affine Lowe in Trans. Cambridge Philos. Soc. 6: 525. 1838), nom. cons. prop. Typus: Portugal, Madeira, Ribeiro Frio, by the Levada to the right, 1 Nov 1828, Lowe (K [on 3 sheets] barcodes K000351173, K000351174 & K000351175). (H) Dryopteris affinis Kinahan in Phytologist 5: 197. 1856, nom. rej. prop. Lectotypus (vide Fraser-Jenkins & Corley in Brit. Fern Gaz. 10: 222–223. 21 Mar 1973): Azerbaidjan, Karabakh: Helenendorf [= Khanlar], 1836, Hohenacker (LE barcode LE01053081). The name Dryopteris affinis (Lowe) Fraser-Jenk. has been almost universally used since 1979 in Floras and other taxonomic and horticultural works throughout the range of the species in Europe, Macaronesia, NW Africa, Turkey, the Caucasus and N Iran. It has been used in a strict sense, as a diploid species, or in an aggregate sense, as the name for the whole cytologically complex apomictic aggregate, in both cases containing subspecies within it of various different cytotypes, diploid, triploid or tetraploid. Many important works from three continents, including every country in Europe, utilize the name D. affinis (Lowe) Fraser-Jenk. Approximately 300 works accepting it are known to us, as opposed to 3 works utilising D. affinis Kinahan (attributed to "(Newman) Kinahan"), one of which is now in the process of amendment. A geographical selection of works accepting D. affinis (Lowe) Fraser-Jenk. includes Heywood (in Tutin & al., Fl. Eur., ed. 2, 1: 1–33. 1993), Castroviejo & al. (Fl. Iber. 1: 128–144. 1986), Hutchinson & Thomas (Welsh Ferns: 121–143. 1996), Stace (New Fl. Brit. Isles, ed. 4: 35–39. 2019), Jonsell & Karlsson (Fl. Nordica 1: 74–84. 2000), Prelli & Boudrie (Fougères Pl. Alliées Eur.: 361–370. 2021), Euro+Med PlantBase (http://ww2.bgbm.org/EuroplusMed/), Güner & Ekim (Resimli Türkiye Florası 2: 239–263. 2019) and many other local, taxonomic, chemical, horticultural and systematic publications. The name Nephrodium affine Lowe (in Trans. Cambridge Philos. Soc. 6: 525. 1838), on which D. affinis (Lowe) Fraser-Jenk. is based, was lectotypified by Fraser-Jenkins (in Willdenowia 10: 108. 1980). But in 2022, IPNI (International Plant Names Index, http://www.ipni.org) discovered and brought to notice an earlier validation of Dryopteris affinis by Kinahan (in Phytologist 5: 197. 1856), based on Dryopteris filix-mas var. affinis of Newman (Hist. Brit. Ferns, ed. 3: 187. 1854), a synonym of D. caucasica (A. Braun) Fraser-Jenk. & Corley (in Brit. Fern Gaz. 10: 222. 1972). Newman (l.c.) based his varietal name on Aspidium affine Fisch. & C.A. Mey. (in Bull. Soc. Imp. Naturalistes Moscou 11: 240. 1838), non Blume (1828). Another species name based on A. affine and cited by Newman was Polystichum affine Ledeb. (Fl. Ross. 4: 515. 1853), but this is also illegitimate as A. caucasicum A. Braun (in Flora 24: 707. 1841) had already been published as a replacement name for A. affine Fisch. & C.A. Mey. and Ledebour should have adopted Braun's epithet. In consequence, Newman's D. filix-mas var. affinis lacks a basionym and so cannot be treated as a new combination, and is, therefore, illegitimate as Newman cited in synonymy Lastrea filix-mas var. incisa T. Moore (in Phytologist 3: 137. 1848), the epithet of which he should have adopted. Consequently, Kinahan's species name is also not a new combination but must be attributed to him alone. As Kinahan based his name entirely on Newman's account, it is to be typified by the type of Newman's varietal name. Although this is superfluous and illegitimate, it is not automatically typified by the type of Moore's varietal name, because, in citing A. affine Fisch. & C.A. Mey. as an intended basionym, Newman indicated a different type, that of Fischer & Meyer's name (Art. 7.5 & Ex. 6). Dryopteris affinis Kinahan was previously unknown, appearing in a note on ferns in a small valley in Ireland, was not listed in any other works and was made inadvertently following Newman's account where the heading was given as Dryopteris affinis, but the text gave it as Dryopteris filix-mas var. affinis and Newman explained that it was a variety of D. filix-mas. Neither Newman nor Kinahan realised that the name applied to the separate species, D. caucasica, not present in Britain, Ireland, or all of W and C Europe, and they had misapplied this D. filix-mas var. affinis and D. affinis to D. filix-mas. Kinahan simply gave the name as "D. affinis Newman", without other nomenclatural information. This earlier D. affinis Kinahan, although also illegitimate, being necessarily typified by the type of D. caucasica, the legitimate replacement name for Aspidium affine Fisch. & C.A. Mey., pre-occupies the name and thus renders D. affinis (Lowe) Fraser-Jenk. an illegitimate later homonym. The disruption and instability caused by the earlier name would be very extensive and would also involve the aggregate having to be referred to by the name, Dryopteris borreri (Newman) Kinahan, of a different cytotype from D. affinis sensu stricto, and the diploid species being changed to D. pseudomas (Woll.) Holub & Pouzar, with many new combinations being required for subsidiary subspecies and varieties, whether treated as a single complex species aggregate, or as in a strict sense as a separate diploid species. Any use of D. affinis ultimately based on Aspidium affine Fisch. & C.A. Mey. would therefore create great disruption in what is already known to be a complex group. Accordingly it is proposed here to conserve the name Dryopteris affinis (Lowe) Fraser-Jenk. against D. affinis Kinahan to maintain nomenclatural stability for the species concerned. CRFJ, https://orcid.org/0000-0003-4490-8523 FJR, https://orcid.org/0000-0003-4459-6769 LE, https://orcid.org/0000-0003-3947-787X ACP, https://orcid.org/0000-0001-6021-9360 We are especially grateful to Prof. J. McNeill and Dr J. Wiersema for their thorough elucidation of the complex nomenclature of Kinahan's Dryopteris affinis and for editorial corrections.

Key messageOur results indicate the existence of interploidy gene flow in Cystopteris fragilis, resulting in sexual triploid and diploid gametophytes from pentaploid parents. Similar evolutionary dynamics might operate in other fern complexes and need further investigation.Polyploidization and hybridization are a key evolutionary processes in ferns. Here, we outline an interploidy gene flow pathway operating in the polyploid Cystopteris fragilis complex. The conditions necessary for the existence of this pathway were tested. A total of 365 C. fragilis individuals were collected covering representatives of all three predominant ploidy levels (tetraploid, pentaploid, and hexaploid), cultivated, had their ploidy level estimated by flow cytometry, and their spores collected. The spores, as well as gametophytes and sporophytes established from them, were analysed by flow cytometry. Spore abortion rate was also estimated. In tetraploids, we observed the formation of unreduced (tetraploid) spores (ca 2%). Collected pentaploid individuals indicate ongoing hybridization between ploidy levels. Pentaploids formed up to 52% viable spores, ca 79% of them reduced, i.e. diploid and triploid. Reduced spores formed viable gametophytes, and, in the case of triploids, filial hexaploid sporophytes, showing evidence of sexual reproduction. Some tetraploid sporophytes reproduce apomictically (based on uniform ploidy of their metagenesis up to filial sporophytes). Triploid and diploid gametophytes from pentaploid parents are able to mate among themselves, or with "normal" reduced gametophytes from the sexual tetraploid sporophytes (the dominant ploidy level in the sporophytes in this populations), to produce tetraploid, pentaploid, and hexaploid sporophytes, allowing for geneflow from the pentaploids to both the tetraploid and hexaploid populations. Similar evolutionary dynamics might operate in other fern complexes and need further investigation.

Abstract Premise Few studies have explored competition in fern gametophyte populations. One limiting factor is the tedious measurement of gametophyte size as a proxy for biomass in these small plants. Here, an alternative approach of estimating the number of green pixels from photos was employed to measure the competitive interactions among apomictic and sexual Dryopteris gametophytes. Methods We cultivated the gametophytes of two apomictic (diploid and triploid) and one sexual (tetraploid) Dryopteris species in monocultures and in two‐species mixtures in the ratios 1 : 1 and 1 : 3. The total gametophyte cover of each population originating from 20 spores was assessed using Easy Leaf Area. Assessments were performed weekly between weeks 4 and 10 of cultivation. Additionally, during week 5, the cover of each species in each mixture was estimated separately. Results We identified a positive correlation between gametophyte size and ploidy level as well as sexual reproduction. The performance of the tested species in mixtures was dependent on the competitor species identity, indicating the importance of competition between gametophytes. Discussion The methods outlined can be used for a rapid assessment of fern gametophyte cover in large gametophyte populations. Ploidy level and reproduction type seem to play a major role in the competitive abilities of fern gametophytes, but more research is needed on this topic.

Premise of research. The gametophytes of ferns are nutritionally independent of the sporophytes and are potentially hermaphroditic. The sexual expression of fern gametophytes is based on environmental cues. To prevent excessive self-fertilization, fern gametophytes employ strategies to increase mating between gametophytes. One of these strategies relies on antheridiogens, pheromones released by older gametophytes and absorbed by younger gametophytes. There are multiple distinct antheridiogen types, some of which are poorly understood and in need of further examination. A still-unresolved antheridiogen type was described in Asplenium ruta-muraria.Methodology. We employed cultivation experiments using spores of 12 fern species to assess the extent and uniqueness of the antheridiogen released by A. ruta-muraria. We tested antheridiogen interactions between representatives of three well-established antheridiogen types and A. ruta-muraria to assess their uniqueness. Furthermore, the effect of potentially antheridiogen-releasing gametophytes of A. ruta-muraria on multiple Asplenium species was examined. Germination in darkness in response to antheridiogens was also tested.Pivotal results. The younger gametophytes of A. ruta-muraria did not respond to the presence of older conspecific gametophytes in a way that could be attributed to antheridiogens. No antheridiogen interactions between A. ruta-muraria and any other species were observed. Nevertheless, the exudates of older A. ruta-muraria gametophytes may affect the development of younger conspecific and interspecific gametophytes.Conclusions. On the basis of its interaction with representatives of known antheridiogen types and the lack of germination in darkness, we conclude that our sample of A. ruta-muraria does not use antheridiogens. This discrepancy between our experiment and the initial publication describing antheridiogens in A. ruta-muraria may have been caused by intraspecific genetic variability within the species. The studied individual of A. ruta-muraria may be able to affect the growth of other gametophytes by other means, possibly via allelopathy, although this aspect of gametophyte interaction is poorly understood.

PREMISE:Apomixis and hybridization are two essential and complementary factors in the evolution of plants, including ferns. Hybridization combines characteristics from different species, while apomixis conserves features within a lineage. When combined, these two processes result in apo-sex hybrids. The conditions leading to the formation of these hybrids are poorly understood in ferns.METHODS:We cultivated spores from 66 fern samples (43 apomicts, 7 apo-sex hybrids, and 16 sexuals), and measured their development in vitro over 16 weeks. We evaluated germination, lateral meristem formation rates, sexual expression, and production of sporophytes and then compared ontogenetic patterns among the three groups.RESULTS:The three examined groups formed antheridia (male gametangia) but differed in overall gametophyte development. Sexual species created archegonia (female, 86% of viable samples), but no sporophytes. Apomicts rarely created nonfunctional archegonia (8%) but usually produced apogamous sporophytes (75%). Surprisingly, apomictic and sexual species showed similar development speed. The sexually reproducing parents of viable studied hybrids formed about twice as many meristic gametophytes as the apomictic parents (39% vs. 20%, respectively).CONCLUSIONS:We present the most thorough comparison of gametangial development of sexual and apomictic ferns, to date. Despite expectations, apomictic reproduction might not lead to earlier sporophyte formation. Apomicts produce functional sperm and thus can contribute this type of gamete to their hybrids. The development patterns found in the parents of hybrids indicate a possible increase of hybridization rates by antheridiogens. The apo-sex hybrids always inherit the apomictic reproductive strategy and are thus capable of self-perpetuation.

The delimitation of lineages in the Cystopteris fragilis complex is complicated by the presence of multiple cytotypes and a lack of defining morphological characters. One character, the production of rugose instead of regular spiny spores, is sometimes associated with a potential Scottish endemic, C. dickieana; however, whether this character is associated with a distinct lineage is uncertain. To better understand the diversity in the C. fragilis complex, we selected 87 C. fragilis samples of known ploidy (4x, 5x, 6x) for sequencing of two plastid loci and we assessed their spore types. These samples represent the variability found in Northern Hemisphere populations, including the type locality of C. dickieana in Scotland. Our analyses revealed two haplotype lineages, which we label the hemifragilis and reevesiana clades, based on their potential relationship to the two presumed diploid parents of C. fragilis. Hexaploids and tetraploids were both polyphyletic. Rugose spores were rarer overall (26% of samples), but five times more prevalent in the hemifragilis clade. Although proper delimitation and understanding of C. fragilis remains a challenge, this study further describes great genotypic and cytotypic complexity present in this complex. Furthermore, rugose-spored plants are widely distributed and should not be associated with a single name.

Wild edible plants have become an attractive variation of the human diet, especially in East Asia, North America, and Oceania. However, their potential in nutrition is only rarely considered in Europe. This study aims to reveal the nutritional and antioxidant potential of mature fern leaves from 13 families grown in Europe. We found that most of the examined fern species displayed a high antioxidant capacity, exceeding 0.5 g Trolox equivalent per gram of extract dry weight in ORAC assay and reaching IC50 values lower than 30 mu g.mL(-1) in DPPH assay (with the value for Trolox 7 mu g.mL(-1)). Most of the species also appeared to be a good source of carotenoids, especially of lutein (205 mu g.g(-1) DW on average) and beta-carotene (161 mu g.g(-1) DW on average) when compared to the reference leafy vegetables spinach and rocket. A cytotoxicity test using ovine hepatocytes showed a non-toxicity effect of fern leaf extracts.

Ferns are part of the diet and traditional medicine in East Asia, North America, and Oceania, however, their importance has been forgotten in Europe. Here, the nutritional and antioxidant potential of young fern fronds (fiddleheads) of eight families were studied. Most of the tested fern species excelled in high antioxidant capacity when compared to the reference leafy vegetables spinach and rocket. On average, the total phenol content reached 220 mg·g−1 of extract dry weight for all fiddleheads, and 15 out of 24 tested species exceeded 1 g Trolox equivalent per gram of extract dry weight in Oxygen Radical Absorbance Capacity (ORAC) assay. On the other hand, fiddleheads contained a comparable amount of carotenoids and ascorbic acid with the reference vegetables. In the case of fatty acid composition, fiddleheads contained especially high amounts of essential omega-3 (n3) and omega-6 (n6) polyunsaturated fatty acids with a beneficial n6/n3 ratio. The n6/n3 ratio in all tested species was between 2 and 6.4, whereas the ratio in the reference vegetables was below 0.4. All in all, fiddleheads from European ferns are a rich source of valuable antioxidants and essential fatty acids with a desirable n-6/n-3 ratio and may thus form an alternative source of these compounds, especially for those people not consuming fish and fish products.

Summary Sex expression of homosporous ferns is controlled by multiple factors, one being the antheridiogen system. Antheridiogens are pheromones released by sexually mature female fern gametophytes, turning nearby asexual gametophytes precociously male. Nevertheless, not all species respond. It is still unknown how many fern species use antheridiogens, how the antheridiogen system evolved, and whether it is affected by polyploidy and/or apomixis. We tested the response of 68 fern species to antheridiogens in cultivation. These results were combined with a comprehensive review of literature to form the largest dataset of antheridiogen interactions to date. Analyzed species also were coded as apomictic or sexual and diploid or polyploid. Our final dataset contains a total of 498 interactions involving 208 species (c. 2% of all ferns). About 65% of studied species respond to antheridiogen. Multiple antheridiogen types were delimited and their evolution is discussed. Antheridiogen responsiveness was not significantly affected by apomixis or polyploidy. Antheridiogens are widely used by ferns to direct sex expression. The antheridiogen system likely evolved multiple times and provides homosporous ferns with the benefits often associated with heterospory, such as increased rates of outcrossing. Despite expectations, antheridiogens may be beneficial to polyploids and apomicts.

Polyploidization is an important speciation and evolution mechanism in ferns. Initially, new cytotypes face challenges in maintaining themselves within the majority cytotype populations. Unlike in most even-ploidy cytotypes, fern triploids are often apomictic or infertile, due to genetic imbalance. An interesting opportunity to study these phenomena has emerged with the discovery of triploid bracken (Pteridium aquilinum), a triploid fern that is fertile but not apomictic. Originally found in one Welsh population, the distribution of this cytotype in Europe is unknown as is its origin and how it maintains itself among the presumed diploid majority. We sampled 135 populations of P. aquilinum, focusing on Central Europe. Ploidy level of all samples was analyzed by flow cytometry. We compared the two cytotypes via micromorphological characters (spore and stomata size), fertility characteristics (spore abortion and proportion of populations with sporangia-bearing fronds). Additionally, genetic difference between ploidy levels was tested as well. The diploid cytotype of P. aquilinum is dominant in continental Europe with 121 entirely diploid populations found, but we also found 9 mixed and 5 entirely triploid populations. Fertile diploid and triploid plants were found only in 17.7% and 21.4% of populations, respectively. The cytotypes are distinguishable using both tested micromorphological characters, but stomata are more reliable due to overall reduced fertility. Unlike the Welsh specimen, our tested triploid has most spores aborted, ca 97.4%, compared to mean 6.0% of spores aborted in diploids. The triploid cytotype is rare and likely originated multiple times from the diploids and relies on clonal and possibly limited sexual reproduction to maintain itself. However, diploids and triploids are often genetically different within a population, indicating that the triploid may migrate between populations. Due to its vegetative growth and presumed continuous formation, the triploid cytotype is likely to remain established in Central Europe, although in small numbers.

BACKGROUND AND AIMS:Polyploidy has played an important role in the evolution of ferns. However, the dearth of data on cytotype diversity, cytotype distribution patterns and ecology in ferns is striking in comparison with angiosperms and prevents an assessment of whether cytotype coexistence and its mechanisms show similar patterns in both plant groups. Here, an attempt to fill this gap was made using the ploidy-variable and widely distributed Cystopteris fragilis complex. METHODS:Flow cytometry was used to assess DNA ploidy level and monoploid genome size (Cx value) of 5518 C. fragilis individuals from 449 populations collected over most of the species' global distributional range, supplemented with data from 405 individuals representing other related species from the complex. Ecological preferences of C. fragilis tetraploids and hexaploids were compared using field-recorded parameters and database-extracted climate data. KEY RESULTS:Altogether, five different ploidy levels (2x, 4x, 5x, 6x, 8x) were detected and three species exhibited intraspecific ploidy-level variation: C. fragilis, C. alpina and C. diaphana. Two predominant C. fragilis cytotypes, tetraploids and hexaploids, co-occur over most of Europe in a diffuse, mosaic-like pattern. Within this contact zone, 40 % of populations were mixed-ploidy and most also contained pentaploid hybrids. Environmental conditions had only a limited effect on the distribution of cytotypes. Differences were found in the Cx value of tetraploids and hexaploids: between-cytotype divergence was higher in uniform-ploidy than in mixed-ploidy populations. CONCLUSIONS:High ploidy-level diversity and widespread cytotype coexistence in the C. fragilis complex match the well-documented patterns in some angiosperms. While ploidy coexistence in C. fragilis is not driven by environmental factors, it could be facilitated by the perennial life-form of the species, its reproductive modes and efficient wind dispersal of spores. Independent origins of hexaploids and/or inter-ploidy gene flow may be expected in mixed-ploidy populations according to Cx value comparisons.

Research on the Czech flora has a long tradition and yielded a large number of records on the occurrence of plants. Several independent electronic databases were established during the last three decades in order to collect and manage these records. However, this fragmentation and the different characteristics of each database strongly limit the utilization and analyses of plant distribution data. Solving these problems was one of the aims of the Centre of Excellence PLADIAS (Plant Diversity Analysis and Synthesis. 2014-2018). which is also the source of the name of the central database of the project: Pladias - Database of the Czech Flora and Vegetation (www.pladias.cz). We developed an occurrence module as a part of the Pladias database in order to integrate species occurrence data on vascular plants in the Czech Republic for use in pure and applied research. In this paper, we present a description of the structure of this database, data handling and validation, creation of distribution maps based on critically evaluated records as well as descriptions of the original databases and explorative analyses of spatiotemporal and taxonomic coverage of the integrated occurrence data. So far we have integrated more than 13 million records of almost 5 thousand taxa (species, subspecies, varieties and hybrids). which came from five large national databases. seven regional projects and records collected within the PLADIAS project. The Pladias database is now the largest set of data on vascular plant occurrence in the Czech Republic, which is subject to continuous quality control. Analyses of this database pointed to differences in spatial and taxonomic coverage of the source datasets. However, it also showed that the targeted effort of experts focused on validating existing records, as well as the collection of new data is still necessary in order to obtain reliable distribution data for individual species.

Recent studies investigating the evolution of genome size diversity in ferns have shown that they have a distinctive genome profile compared with other land plants. Ferns are typically characterized by possessing medium-sized genomes, although a few lineages have evolved very large genomes. Ferns are different from other vascular plant lineages as they are the only group to show evidence for a correlation between genome size and chromosome number. In this study, we aim to explore whether the evolution of fern genome sizes is not only shaped by chromosome number changes arising from polyploidy but also by constraints on the average amount of DNA per chromosome. We selected the genus Asplenium L. as a model genus to study the question because of the unique combination of a highly conserved base chromosome number and a high frequency of polyploidy. New genome size data for Asplenium taxa were combined with existing data and analyzed within a phylogenetic framework. Genome size varied substantially between diploid species, resulting in overlapping genome sizes among diploid and tetraploid spleenworts. The observed additive pattern indicates the absence of genome downsizing following polyploidy. The genome size of diploids varied non-randomly and we found evidence for clade-specific trends towards larger or smaller genomes. The 578-fold range of fern genome sizes have arisen not only from repeated cycles of polyploidy but also through clade-specific constraints governing accumulation and/or elimination of DNA.