Weedy ferns (Polypodiopsida) in Argentina: diversity, distribution and impact on human activities and ecosystems.

Currently, in Argentina 368 species of true ferns (i.e. Polypodiopsida class) are distributed throughout the country, however, only four of them have been mentioned until now as weeds and ruderal species. The goal of this work was to generate an update of weedy ferns from Argentina, including morphology, distribution, and type of weed according to their impact on natural habitats and/or human activities. All Argentinian fern species were analyzed based on references, herbarium specimens, and field trips. As a result of our study 25 species were recorded from Argentina and classified as segetal, ecological, or aquatic weeds, and ruderal and/or toxic species. Current taxonomic identity, diagnostic characters, origins, habitats, geographical distribution, common names, and impact and potential risks were indicated by species. In addition, we provide a dichotomous key to species, presence of these species in southern South American countries, as well as and photographs in natural habitat. This work represents the first review on native and exotic ferns from Argentina that cause an impact on human activities or disturbe native habitats. The results provide information for the development of weed management tools and priority areas to implement them.


INTRODUCTION
This work represents the first contribution on the weedy "fern" or "true ferns" species (Polypodiopsida sensu PPG I) that grow in Argentina and their relationships with natural habitats and human activities. Previously, until more than a decade ago, the ferns and lycophytes (Lycopodiopsida class sensu PPG I 2016) were grouped in the paraphyletic clade "Pteridophytes" but they later separated based on morphological and molecular data (Smith et al. 2006).
Phylogenetically, Polypodiopsida is the sister group of the seed plants and consists of about 10578 species in the world (PPG I 2016), of which 368 are present in Argentina (Ponce & Arana 2016). Although ferns are usually recognized by humans due to their ornamental and/or medicinal uses, more than 157 species in the world have been registered as alien weeds, of which 39% behave as invasive species (Jones et al. 2018) or toxic for animals and humans (Siman et al. 2000). The controversial term "weed" can be defined, in a broad sense, as those plant species that interfere with human activity because they grow at a time and place where they are unwanted (Holzner 1978, Fryer 1979. From a biogeographical perspective, "weeds" are considered exotic species that are distributed outside their native distribution area due to an unnatural cause (Rejmánek 1995). However, if ecological changes occur under man-made management systems, species of the native flora can expand their range of distribution and invade new habitats (Mortimer 1990). From an ecological perspective, "colonizing weeds" are considered those pioneer species that rapidly invade those areas where the original vegetation was altered (Baker 1974, Pysek 1995, Wijesundara 2017. Colonizing species can be considered as weeds because they invade cultivable areas and decrease the productivity of the crop (segetal weeds), and because they invade disturbed natural habitats and, if these are exotic, they could displace native species (environmental or ecological weeds) (Holzner 1978, 1982, Lorenzi 2008. Furthermore, some aquatic species can also be considered colonizing weeds, when their populations grow excessively under favorable environmental conditions. These populations reach to cover completely bodies of water hindering navigation, fishing, and electrical generation, and contributing to the ecosystem eutrophication due to the symbiosis of aquatic species with Cyanobacteria (Randall 1996).
On the other hand, other species are considered weeds but because of their toxicity. In addition to the risk to human health, the poisoning caused by the ingestion of toxic plants is one of the main causes of mortality of livestock animals and causes great economic losses (Gallo 1979, Acamovic et al. 2004, Campos et al. 2016. Finally, sometimes the concept "weed" includes those species called "ruderals". These species grow spontaneously in urban microhabitats such as stone or brick walls, roofs, roadsides, and margins of railway lines, and ditches (Holzner 1978, Caluff & Fiallo 2008, Edgington 2008, Morajkar et al. 2015. Although in many cases the ruderal species do not cause a direct impact on the anthropic activities, and even provide an ecosystem service, their excessive growth for a long time can turn them into "annoying" or unwanted species (Del Tredici 2010).
It is important to note that the recognition of a species as a weed varies according to the region and over time, since it depends on the subjectivity of the human with respect to the problems that the species causes (Marzocca 1986, Binggeli 1994.
Ferns have reproductive strategies that in many cases coincide with those of a colonizing weed. Among these can be highlighted: production of thousands of anemophilous spores that are dispersed hundreds of kilometers and remain dormant for years forming a spores bank in the soil (Tryon 1986); rapid and massive germination and young fastgrowing sporophytes; long creeping rhizomes sometimes fire-resistant (Roos et al. 2010); vegetative multiplication through fragmentation and/or through gemmiferous rhizomes, rachis, and leaves (Vasco et al. 2013), and production of allelopathic substances that inhibit the growth of other species. In this way, exotic species of ferns have displaced native representatives in different parts of the world, producing numerous adverse effects on the ecosystems that invade (Sharpe et al. 2010, Akomolafe & Rahmad 2018.
Despite the important diversity of ferns in the Argentine flora, only four species were considered weeds in general or local works as weeds (Marzocca 1986, Lallana 1989, Califano & Echazú 2013, Rosato et al. 2015, Fernández et al. 2016. The goals of this work are (1) to suggest which among the fern species present in the Argentine flora behave as weeds (including ruderal) and to review their taxonomic and morphological diversity, (2) to update information about their
From a taxonomical point of view, the 25 species belong to 16 genera and ten families of Polypodiopsida. The families most represented were Pteridaceae, with 11 mostly ruderal and toxic species, followed by Salviniaceae, with six aquatic weeds.
Regarding the original distributions, 14 of the weedy species are native and widely distributed in the country. Of these, twelve occur in three out of five regions of Argentina (Fig. 3). The remaining 11 species are exotic and, in most cases, their introduction into the country may be due to their ornamental use followed by the establishment beyond human control. However, the causes of the introduction of Macrothelypteris torresiana (Gaudich.) Ching, Pteris cretica L., and Salvinia adnata Desv remain unknown.
Geographically, the highest number of species (21) is recorded in the Central region, and the lowest number (five) in the Patagonian region. The province of Salta in Northwest Argentina and the Buenos Aires province in the Central region, recorded the highest weed species richness (18). Furthermore, Salta has the largest number of native weedy species in the country, while Buenos Aires has the largest number of alien weedy species in the country (Fig 2). In contrast, Tierra del Fuego (Patagonian region) is the province where the lowest number of weedy species was observed, just two: Azolla filiculoides Lam. and Equisetum giganteum L.
Despite the fact that most species identified in the present study are also cited in floras of South American countries, only in some cases these were recognized as weeds (Sagástegui & Leiva 1993, Mattheii et al. 1995, Kissmann 1997, Lorenzi 2008, De Egea et al. 2016 (Fig. 1).
In relation to this, seven Argentinian colonizing weeds (segetals, environmentals or aquatics) are also distributed in Uruguay, six in Brazil, three in Peru, two in Bolivia and only one in Chile and Paraguay. In the case of Argentinian ruderal species, Macrothelypteris torresiana is also distributed in Brazil, Adiantum capillusveneris and Cyrtomium falcatum in Peru, and Nephrolepis cordifolia, Pteris cretica, P. tremula and P. vittata in Uruguay. Pteridium esculentum subsp. arachnoideum and Equisetum giganteum were explicitly recognized as toxic weeds in Brazil and Chile, respectively (Fig. 1).
Finally, three species were explicitly mentioned as weed in the most countries: Azolla filiculoides, Equisetum giganteum and Pteridium esculentum subsp. arachnoideum.        Fig. 4a.

List of species
Weed type: Segetal weed and ecological weed.
Origin area and distribution in Argentina: Native species from Mexico up to central Argentina and southern Brazil . In Argentina, it is distributed on the northwest and northeast, reaching Central region (Fig. 3).
Growth habits / Impact / Relationship to human activities: It is frequent as a large-coverage weed, usually in road margins, understory of degraded native forests, and grazed areas. It has been recorded as a weed in overgrazed field in Entre Ríos province (Cottani & Sabattini 2006), associated with forest crops of Eucalyptus grandis W. Hill in Corrientes province ( Barrett & Tressens 1996), and growing in implanted forests of Pinus elliotti Engelm. and Pinus taeda L. in Córdoba province (Morero 2006). Likewise, the presence of A. chlorophylla in pastures abandoned after agricultural exploitation and its predominance with respect toother pioneer species has been recorded in an experimental field located from Santa Fe province (Etchepare & Boccanelli 2007, Boccanelli & Pire 2011. Observations: A. chlorophylla h as xeromorphic characteristics such as lamina with glandular trichomes, and petioles, rachis and lamina with abundant sclerenchyma tissue. These characters give it ecological plasticity and advantage over competing species to grow in a great diversity of environments (Hernández & Rodríguez 2010). Also, it has robust rhizomes that are fire resistant (Meza Torres et al. 2013a).

Origin area and distribution in Argentina:
It is a cosmopolitan species. In the Americas it is distributed from southern United States and Mexico, throughout Central America, the Caribbean and northern South America up to Chile and Argentina (Davidse et al. 1995). It was cited in floras of Venezuela (Vareschi 1969), Peru (Tryon & Stolze 1989) and Chile (Rodriguez 1995). There are no older references of this species in Argentine flora, but there are records of cultivated specimens at the end of the 19th Century (Hicken s.n., SI). In Argentina, recently it was cited growing on walls at the Natural Reserve of Punta Lara, on the southern coast of Rio de la Plata, Buenos Aires province (Giudice et al. 2011) (Fig. 3).
Growth habits / Impact / Relationship to human activities: It is a ruderal species in urban habitats where it colonizes gardens and pots and grows on brick walls, favored by calcareous substrate.
Observations: Frequently used as ornamental.
Origin area and distribution in Argentina: It is widely distributed in the Americas, on the Southeast and Southwest of Canada and the United States, throughout Central America and South America up to Uruguay and Argentina (Arana 2016). In Argentina, it is distributed mainly from northern and Central regions (Fig. 3).
Growth habits / Impact / Relationship to human activities: This species inhabits lentic water bodies (e.g. ditches, ponds and temporary puddles) and its populations present an annual cycle with periods of growth in the warm season. Its rapid vegetative reproduction by mean of rhizome fragmentation obstructs the passage of light and oxygen in a short time. This alters the balance of the ecosystem and inhibit the growth of submerged vegetation.
Taxonomic notes: Currently, Azolla caroliniana Willd. is a synonym of A. filiculoides (Ponce & Arana 2016) but in previous provincial floras of Argentina were treated as distinct species (Capurro 1968, de la Sota 1977, Ponce 1994.
Additional diagnostic characters: Fronds up to 5 cm length, densely imbricated, green to reddish; segments elliptic to ovate. Morphologically it is very similar to A. cristata and it only differs from this one by microscopic characters (see key to species).

Origin area and distribution in Argentina:
It is widely distributed in the Americas, from Alaska on the North to Tierra del Fuego and Malvinas Islands on the South (Arana 2016). It is present in all the provinces of Argentina (Fig. 3).
Growth habits / Impact / Relationship to human activities: It grows between sea level to 3800 m, on banks of stagnant waters, lakes, ditches, gutters of roads and, less frequently in channels and slow streams. It can cover the entire surface of water body by blocking the light entrance and disturbing the ecological balance of aquatic ecosystem. The massive propagation is facilitated through rhizomes fragmentation and the differentiation in new individuals. This vegetative mechanism constitutes a more common type of reproduction than sexual reproduction. On the other hand, A. filiculoides establishes a symbiosis with the Cyanobacteria Anabena azollae that fixes atmospheric nitrogen. Thus, the excessive growth of the species can generate eutrophication of the environment. In addition, this species can absorb heavy metals from the environment and become potentially toxic to animals (Kissmann 1997).
Mechanical control and control through herbicides have been tested in Azolla filiculoides with few and expensive results. Also, two insect species were identified as possible candidates for the biological control of this weed: Pseudolampsis guttata (Leconte) (Chrysomelidae) and Stenopelmus rufinasus Gyllenhal (Curculionidae) (Hill & Cilliers 1999, McConnachie et al. 2003. Observations: It is one of the most cited weeds for irrigated rice crops (Lallana 2005), paradoxically it can be used as an economic biofertilizer in these crops. Weed type: Toxic. Common names in Argentina: "Helecho petiso", "raki raki".
Origin area and distribution in Argentina: It is distributed from Peru, Bolivia and northern Chile, in Andean and sub-Andean environments to central Argentina . In Argentina, it grows from the Northwest to the Pampean mountains range between sea level to 2000 and 4800 m (Fig. 3). Among fern species, it inhabits the highest number of different ecosystems in the country.
Growth habits / Impact / Relationship to human activities: It is a xeromorphic epipetric species that grows in ravines and rocky slopes, crevices and edges of water springs. C. pruinata affects livestock activity due to its toxicity (Califano andEchazú 2011, 2013). When ingested, it affects the nervous system of animals causing depression, anorexia, muscle fibrillation and locomotor ataxia, decubitus position and, finally, death. It affects especially the offspring of sheep and goats, between 48 to 72 hours after consumption. Cases of poisoning have been detected in Jujuy province localities and towns of the Iruya River Basin, northwestern Argentina, in Salta province where livestock consume it during the spring due to a shortage of other forage species.
Observations: It is used by traditional Andean cultures for the medical treatment of urinary disorders, Chagas disease and postpartum, stomach, menstrual and head pains (Navarrete et al. 2006).
Additional diagnostic characters: Segments with basal pair of adjacent veins joined forming a single vein; circular sori protected by indusia with acicular short and dense hairs; sporangium with one glandular hair on the stalk.

Origin area and distribution in Argentina:
It is a paleotropical species, originally distributed in Africa, Asia, Australia and South Pacific islands. In the Americas, it is introduced and naturalized at present from the southeastern United States to Argentina (e.g. Smith 1971, Holttum 1976. Although the origin of its introduction is not determined, specimens in North America and the Antilles are frequently recorded from 1930 where it could have been dispersed (Strother & Smith 1970). Because in Argentina cultivated specimens are kept at herbaria since 1908 (Hicken 50, SI), probably naturalization of this species could involve independent events in the continent. Christella dentata grows on the northwest and northeast of this country, reaching the Central region (Fig. 3). According to Smith (1971), this species has the most quantity of recorded specimens within Thelypteridaceae.
Growth habits / Impact / Relationship to human activities: It forms dense populations in exposed habitats and colonizes margins of roads, edges of fields, perennial crops and understory of tree plantations such as Pinus sp. and Araucaria sp. It is also found as ruderal, growing in wasteland or on walls in urban and suburban areas. Occasionally, it is cultivated for ornamental purposes. It is a potential invasive species and displacement of native species due to this type of growth has been indicated for Mexico (Tejero-Díez & Torres-Díaz 2012). According to Murakami et al. (2007), urban matrix growth facilitates the expansion of this species since, in an urban environment, it prefers artificial structures such as side walls or bottoms of drainage channels, crevices in stone walls and roadsides instead of forestfloor environments. Furthemore, the roots of C. dentata possess an allelopathic substance, Thelypterin A and B that inhibits gametophytes growth of other ferns (Davidonis 1976). Weed type: Ruderal. Common names in Argentina: "Helecho acebo", "helecho cirtomio".
Origin area and distribution in Argentina: it is native of eastern Asia, mainly in China, Japan, South Korea, and Taiwan. It was introduced worldwide for ornamental use and currently is naturalized in Europe, North America, Oceania, and South Africa with few records in the Caribbean and South America (Ponce & Arana 2016). In Argentina, it was introduced as ornamental due to its successful growth in temperate climates and easy propagation through rhizomes multiplication. It is currently recorded on the east of Argentina (Fig. 3).
Growth habits / Impact / Relationship to human activities: It is a ruderal species frequently associated with urban areas, growing on rocky surfaces of walls, stairs or water wells. This species requires humid or shaded conditions for its establishment and it is sensitive to low temperatures. However, it has a rapid growth once it was established. Colonization of new habitats is facilitated by its apogamic reproduction (Robinson 2009). In Argentina, it is associated mainly with anthropized landscapes; however, in the Caribbean it was recorded in natural areas displacing native species Taxonomic notes: It was cited as Dryopteris patagonica Diem in a floristic work (Diem 1960).

Origin area and distribution in Argentina:
It is distributed in North America, Europe, northern and central Asia and Madagascar; introduced species in New Zealand and South America (Ponce & Arana 2016). In Argentina, it inhabits northern Patagonia (Fig. 3).
Growth habits / Impact / Relationship to human activities: Populations in Argentina were originated from ornamental culture of northwestern Patagonia that escaped in the region of Nahuel Huapi Lake, Neuquén and Río Negro provinces. Also, it has been registered as an invader of degraded and anthropically altered sites in New Zealand like urban and suburban areas (e.g. Christchurch and Dunedin), rural vegetation from unimproved hill country pasture, exotic forest and indigenous forest remnants (Ure 2014). Its role as a colonizing species is due to the tolerance to a wide range of environmental conditions, including soils compacted by livestock, and the long-distance dispersal of its spores. D. filix-mas is used as antiparasitic, and anthelmintic in traditional medicine (Blakemore et al. 1964), and in Argentina, it is an official drug cited by the Argentine Pharmacopoeia (Bandoni et al. 1978) or in phytotherapy (Disposition 2673/99, National Administration of Drugs, Food and Medical Technology). However, its intake must be controlled because it can be very toxic to humans if it is ingested in large quantities. There are records of vomiting, dizziness with visual disturbances to blindness or even death due to the ingestion of this species (Schönfelder & Schönfelder 2001).
Origin area and distribution in Argentina: It is widely distributed in tropical areas of the Americas (Arana 2016). In Argentina it is widely distributed (Fig 3).
Growth habits / Impact / Relationship to human activities: It is an invasive species of grasslands and waterlogged crops, channels and ditches, drainage channels, wasteland and roadsides. Additionally, it represents a serious problem for irrigation systems of crops in flood zones in Brazil and Peru (Sagástegui & Leiva 1993, Zegarra 1996, Lorenzi 2008. Colonization is facilitated by its rhizomes fragmentation. Also, E. giganteum is toxic for horses and other domestic animals because it produces antithiaminic substances that causes weight loss, weakness, signs of paralysis and temporary excitement by its ingestion (Alvin-Carneiro 1948, Kissmann 1997, Riet-Correa et al. 2017). On the other hand, the aqueous extract of vegetative organs shows allelopathic principles that inhibit seed development (Franco et al. 2014).
Observations: Equisetum hyemale L. is a close species that was recently identified as a problematic invasive in Uruguay (C. Brussa comm. pers.). Because this species is cultivated in Argentina studies are necessary for avoiding its probable invasion in this country.
Origin area and distribution in Argentina: It is a Paleotropical species, distributed from tropical and subtropical Africa, Asia, and the Pacific islands . In the Americas, it is a widely naturalized species from the United States to southern Brazil and central Argentina (Fig 2).
Growth habits / Impact / Relationship to human activities: It grows in modified and open habitats such as margins of ditches and roads, embankments, margins of railways, associated with sandy or rocky soils, or lands covered with litter. In Argentina, it invades forests of Araucaria angustifolia (Gaudich.) Ching on the east of the country (Meza Torres et al. 2013b). In addition, it is registered as ruderal since 1960 (Burkart 21520, SI). Potential colonizing of M. torresiana is mainly due to the enormous production of spores several times by year.
Observations: This species is considered a source of anti-cancer drugs because recent studies detected flavonoids in the roots with antitumor action in vitro (Huang et al. 2010).
Additional diagnostic characters: two pairs of opposing pinnae on a very short rachis (resembling a clover with four leaflets), floating; petioles up to 20 cm long, submerged; sporocarps growing under the substrate.

Origin area and distribution in Argentina:
It is distributed in the Americas from Mexico up to southern Argentina. In Argentina inhabits from the north of the country up to northern Patagonia (Fig. 3).
Growth habits / Impact / Relationship to human activities: It inhabits lentic environments such as banks of ponds, dams and temporary water puddles. It is a frequent weed of rice crops. Its main colonization strategies are the vegetative fragmentation of rhizomes and the presence of closed reproductive bodies (sporocarps) within which spores can resist dormant in soils flooded for many years.
Observations: The enzyme Tiaminase I, which promotes the breakdown of thiamine (Vitamin B1), has been found in the leaves of Marsilea species. This process represents a risk of intoxication for livestock (Skalski et al. 2016). Additional diagnostic characters: Rhizomes with branched stolons with gemmiferous tubers; laminae pinnate with strongly reduced base; pinnae patent or slightly falcate, with unequal base, rounded apex and dentate margin.

Origin area and distribution in Argentina:
It is distributed as native from Africa, southeastern Asia, Indochina, Australia, New Zealand and the Pacific Islands, and probably northern South America and the Caribbean (Hovenkamp & Miyamoto 2005). In the remaining Neotropical countries, it is probably a crop escape. This species is naturalized in Argentina, Bolivia, Brazil, Paraguay, and Peru. In Argentina, it is distributed from the north to the center of the country (Fig. 3).
Growth habits / Impact / Relationship to human activities: This species forms dense populations in a very short time due to a rapid rhizomes growth and production of many stolons with tubers. In Argentina, it is a spontaneous species in urban and suburban areas, on walls and roofs of abandoned buildings, and has been frequently recorded on trunks of Melia azedarach L. and Phoenix or Butia species. It is also part of the Global Invasive Species Database. Nephrolepis cordifolia has been introduced in different countries around the world because its use as ornamental. In the United States (Florida estate), it alters and displaces native species, changing structure or ecological functions of the community and hybridizing with native taxa (Langeland 2014).

Origin area and distribution in Argentina:
It is widely distributed in the Americas, from southern United States up to central Argentina (Arana 2016). In Argentina, it inhabits from the Andean Mountains on the Northwest of the country (reaching 4300 m u.s.l.) up to Sierra de la Ventana mountain range (reaching ca. 1200 m u.s.l.) in southern Buenos Aires province in the pampas region (Fig. 3).
Growth habits / Impact / Relationship to human activities: It is usually recorded on walls in urban areas because it is a xeromorphic species that grows in nature on mountains, hills and ravines. It is a toxic for livestock, goats and sheeps, especially in northwestern Argentina (Califano & Echazú 2013). This species and Cheilanthes pruinata, both named "chujchu" by Andean people, are mentioned as having similar effects on livestock (Villagrán et al. 2003).

Origin area and distribution in Argentina:
It is widely distributed in the Americas from southern United States to central Argentina ( Giudice & Luna 2016). In Argentina, it inhabits from the northwest of the country up to the Río de la Plata region (Fig. 3).

Growth habits / Impact / Relationship to human activities:
It usually grows in anthropized environments such as margins of crops, roadsides, channels and ditches. In the outskirts of San Miguel de Tucumán, it was observed forming dense populations in the margins of maize plantations (Yañez et al. 315 BA).
Origin area and distribution in Argentina: It is distributed in the tropical and subtropical regions of the Americas (Schwartsburd et al. 2018). In Argentina, it inhabits rocky soils from the northwestern Andean Mountains and northeastern subtropical forests up to Balcarce mountains in Buenos Aires province in the pampas region (Fig. 3). It was recorded in sandy islands of the Paraná Delta by Burkart (1933) and Capurro (1968).
Growth habits / Impact / Relationship to human activities: This species is one of the best known weeds in the world for its aggressiveness to colonize and modify habitats disturbed by anthropic activity, such as pastures, abandoned fields and deforested lands. This species presents a double system of branched, underground rhizomes, very difficult to remove (Watt 1940) and that is fire-resistant. This last characteristic allows the species to grow even in those regions where the burning of vegetation is the most frequent method to clean fields destined for planting (Roos et al. 2010). In addition, the reproductive success of this species is due to the enormous production of spores that are easily dispersed by the wind and germinate in short periods. Once the populations are established, the growth of other plant species is hindered because fronds up to 4 m length are scandent and form a thick covering that limits the germination of remaining seeds in the soil. Likewise, decomposing fronds release phenolic compounds that interfere in an allelopathic way, inhibiting the germination of seeds and the establishment and growth of possible competitors (Silva Matos & Belinato 2010, Xavier et al. 2016. As a defense mechanism against consumers, the species produces cyanogenic glycosides that, through their hydrolysis, release hydrogen cyanide (Oliveros-Bastidas & Alonso-Amelot 2010). Finally, in addition to invading altered habitats, intoxication events of livestock animals have been recorded by ingestion of this species for a long time (Marrero Faz & Calderón Tobar 2012, Furlan et al. 2014 due to the concentration of toxic Ptaquiloside in the aerial parts of the plant. This problem has been registered in Argentina, mainly in the northwest region (Marin et al. 2004, Marín 2011. In humans, carcinogenesis caused by ingestion or continuous contact with the species was also recorded (Simán et al. 2000, Recouso et al. 2003, Tourchi-Roudsari 2014.
Various mechanisms such as herbicides, mechanical extraction and the use of competing native species were used to control this species (Roos et al. 2011, Aguilar-Dorantes et al. 2014. Observations: Colonization of new habitats by Pteridium species has been matched with human activity throughout history. In spite of genus origin was dated to the Miocene, its role as an invasive species has been recorded during the Mesolithic associated with modifications of natural environments by the human being (Rymer 1976 albo-lineata (Capurro 1968, Martinez & Prado 2016. Recently, following the works of Shieh (1966) and Jaruwattanaphan et al. (2013), Guerrero et al. (2017 redefined them as P. nipponica. In the present work, Martínez & Prado (2016) were followed because it is considered that more studies are needed about the infraspecific variability of this complex species to take taxonomic decisions.

Origin area and distribution in Argentina:
It is distributed in the Paleotropical region and naturalized in the Americas from southeastern United States to southern Argentina, in the Malvinas archipelago (Martinez & Prado 2016).
Growth habits / Impact / Relationship to human activities: It is a very common species in disturbed and ruderal environments, such as roadsides or humid walls. It is registered as an apogamic species (Walker 1962, Martínez 2010 and, probably, this characteristic is related to the cosmopolitan distribution of the species and the facility to colonize new environments. According to Global Invasive Species Database, this species has caused the displacement of other native species in the USA. Additional references: Morton (1957), Martínez & Morbelli (2009), Martínez (2011 (and P. plumula Desv., see below) with this disease was verified (Micheloud et al. 2017).

A d d i t i o n a l d i a g n o s t i c c h a ra c te rs:
Morphologically, it is similar to juvenile forms of P. cretica. However, they can be easily distinguished by the winged or wingless rachis (see key).

Origin area and distribution in Argentina:
It is distributed in tropical Asia and is widely naturalized in the Americas, from southeastern United States to the center of Argentina (Martinez and Prado 2016). In Argentina, it has been recorded in two disjunct areas: both Buenos Aires city and province in the pampas, and in the north of the country up to 1200 m u.s.l (i.e. Chaco and Salta provinces).
Growth habits / Impact / Relationship to human activities: It grows in ruderal habitats, on humid walls. In addition, this species has been defined as an ecological weed in other areas of its distribution (Murakami et al. 1997). Apogamous reproduction has been detected in this species (Kawakami et al. 1995) and selffertilization events of gametophytes has been studied, which could be related to an adaptive advantage for the colonization of open and distant habitats (Watano 1988).
Observations: As in the case of P. cretica, there are ornamental cultivars for this species. According to Burkart (1933), this could be the origin of the spontaneous populations that are observed in Buenos Aires city.
Additional diagnostic characters: Fronds up to 2 m long, dimorphic, pale green; petiole pale brown to chestnut-brown; rachis red-brown; last sterile segments up to 3 mm wide, narrowoblong to linear, slightly toothed margins; last fertile segments up to 1.5 mm wide.

Origin area and distribution in Argentina:
It is originally distributed in Australia (Orchard 1998). In Argentina, it is a common cultivated species that is a spontaneous in urban areas of both Buenos Aires city and province. However, according to Martínez & Prado (2016) it is not a naturalized species in the country.
Growth habits / Impact / Relationship to human activities: In Argentina, it is usually found as a ruderal species on walls, growing sub-spontaneous in gardens or on the banks of the Paraná river. Also, it is observed growing in protected areas of the province as Parque Natural Municipal Ribera Norte (San Isidro), Reserva Natural Avellaneda (Avellaneda) y Reserva Natural Punta Lara (Punta Lara) (Berrueta com pers.). Burkart (1933) noted that spontaneous specimens were smaller than those cultivated and often it were sterile. However, the specimens observed in the aforementioned protected areas are fertile. It is important to follow the naturalization process of this species with the objective of evaluating a possible displacement of native flora species. Taxonomic notes: According to early works, Argentine specimens were identified as P. longifolia L. (Burkart 1933, Capurro 1938, Capurro 1968, Cabrera & Zardini 1978. However, later on, de la Sota & Morbelli (1985) based on an exhaustive morphological analysis, determined that these specimens actually correspond to P. vittata and excluded P. longifolia of this country.
Additional diagnostic characters: Fronds pinnate with pinnae entire, sessile and linear. This species varies enormously in other frond traits and in size, density and color of rachis scales.

Origin area and distribution in Argentina:
It is distributed in the east of Asia, and naturalized in the Americas ( Martinez & Prado 2016). In Argentina, it inhabits from the north to the center of the country, and in Buenos Aires city have been recorded spontaneous near its harbor from the early 20th Century (Burkart 1933) Growth habits / Impact / Relationship to human activities: It has been introduced in the Americas with ornamental proposes. It is a ruderal species that grows sub-spontaneously in wall crevices with calcareous substrate. It is usually found on old houses roofs or abandoned buildings. It is a drought-resistant species, and can grow without soil, in shaded or sunny environments. It causes gradual substrate deterioration.
Origin area and distribution in Argentina: It is distributed originally in southeastern Brazil. However, currently it has invaded tropical and subtropical regions around the world reaching 31 countries of four continents where it has become a worrisome weed (Luque et al. 2014). In many cases, introductions were due to its ornamental use in fish tanks and fountains. In Argentina, according to Arana (2016), it has been only recorded in the Iberá wetlands, Corrientes province. However, it is a doubtful species in Argentina since we could not find the unique cited specimen of the species for the country (Forno s.n., Z).
Growth habits / Impact / Relationship to human activities: According to the Global Invasive Species Database, it is one of the most aggressive weed belonging to the genus Salvinia in Africa, North America, and Oceania. It is a highly competitive species with a great capacity for vegetative proliferation by rhizome fragmentation. It disperses easily and has high tolerance to environmental stress factors such as low temperatures (Arana 2016). Under favorable conditions, this species forms dense populations over 50 cm thick that cover the entire body of water and limit the gas exchange and the photosynthesis process of other plant species, also deteriorating the physical-chemical quality of the water. It affects human activity because it interferes with fishing exploitation, the cultivation of species in flooded soil such as rice, the generation of hydroelectric energy (for obstruction of reservoirs) and maritime transport (Kissmann 1997). One of the methods of biological control frequently used is by Cyrtobagous salviniae which creates tunnels in rhizomes and feeds on buds (Jacono et al. 2001). Even though the species present nowadays a restricted distribution in Argentina, continuous monitoring is required to avoid a potential impacts..
Observations: S. adnata is a hybrid species originated between S. biloba and S. auriculata based on reproductive and morphological data (Loyal & Grewal 1966, Mitchell 1972.

Additional Diagnostic characters:
First pair of floating pinnae up to 20-25 mm long. It differs from S. auriculata complex by the fusion of the apices of the papillae hairs (see dichotomous key).
Origin area and distribution in Argentina: It is widely distributed in the Americas, from the United States and central Mexico to central Argentina, where it was cited from Salta to Buenos Aires provinces (Arana 2016).
Growth habits / Impact / Relationship to human activities: As it happens with other species of the genus, the excessive growth of the populations of this species through vegetative fragmentation obstructs fluvial channels and affects the water quality. Alterations in water and soil quality and reduction of native biodiversity have been recorded because of the species growth by the Global Invasive Species Database. As with Salvinia adnata, it can be controlled by the action of the insect Cyrtobagous salviniae (Parys & Johnson 2013). Salvinia minima is frequently cultivated as ornamental in pools and aquariums due to its small size and thermal tolerance. Although it is registered as a weed in other countries of the Americas, up to now there is no exhaustive survey of its impact in Argentina.
Observations: Salvinia minima has the ability to absorb heavy metals such as arsenic and plumb (Hoffmann et al. 2004).

DISCUSSION
The present study represents an important progress to the knowledge of the colonizing fern species of disturbed habitats (aquatic, ecological, segetal, or ruderal) and / or toxic for livestock animals from Argentina. In this sense, 20 more weedy ferns species are recognized than those mentioned in the last study of Argentinian weeds carried out by Fernandez et al. (2016). This represents an increase from 0.6% to 3% in the percentage of ferns in the Argentina weed list. Likewise, weeds represent 7% of 368 species of ferns recognized in the Argentinian flora (Ponce & Arana 2016).
Among the species studied, Pteridaceae is the best represented family and half of its representatives are exotic. This is consistent with the observations of Jones et al. (2018) who pointed out that, globally, Pteridaceae is the family with most number of species that have become alien.
The present study, also, constitutes the starting point for more exhaustive studies about the ecological role and the distribution of the studied species, which allow to identify suitable environmental conditions for their growth and to detect potential risks for human activities. In this sense, although some species such as Pityrogramma trifoliata, Salvinia adnata and S. minima have restricted distributions ranges and/or their impact is still little known in the country, the problems detected in other countries will contribute to future studies about the inconveniences that these species could cause.
Regarding the geographical distribution of the species, according to the results obtained in this study, the priority region for future analyzes is the central Argentina because the largest number of records of weed ferns was found here. Likewise, the province of Buenos Aires, from the Central region, was one of the two provinces with the largest number of weed species and the province with more exotic weed species. Due to the latter, it would be important to carry out studies in the province concerning the impact caused by exotic species on native flora populations, mainly in protected areas.
Authors studying weedy species in Asteraceae family made similar observations, as the greatest richness of adventitious Asteraceae species are distributed in the province of Buenos Aires (Katinas et al. 2007). The other province with high number of weedy fern species was Salta. High diversity of weedy ferns in Salta may simply reflect that Salta belongs to the Northwest region, one of the main centers of fern diversity in Argentina (Ponce et al. 2002).
Additionally, this survey provides further data to the scarce and fragmented information that up to now exists about the presence of fern species that can affect urban buildings (Bertolami 1990, Franceschi 1996, Franceschi & Boccanelli 2013, Rosato et al. 2015. Most of these species are exotic and only in some cases the origin of their invasion is clearly know. Therefore future studies are need to clarify their introduction to the country and categorize the state of the invasion (Blackburn et al. 2011) and the magnitude of the impact on native species, on the ecosystem structural characteristics or on human activities (Blackburn et al. 2014).
The results of this study provide information for the development of weed management tools and point to priority areas to implement them, distribution modeling and ecological niche modeling of invasive species or sanitary control to livestock where those species are found.