An updated checklist of the Asteraceae of Ñeembucú, Paraguay

. Ñeembucú is one of the least surveyed departments of Paraguay in terms of floristic diversity, largely due to its flooded topography, which has limited the accessibility to its wild areas. Previous work has systematised 676 taxa of vascular plants, demonstrating floristic richness and emphasizing the information gaps that still exist. Considering that Asteraceae is one of the largest botanical families in Paraguay, as an update to the knowledge of the flora of Ñeembucú, we present here an updated list of 88 species of Aster-aceae from the Ñeembucú region, represented by 58 genera within 17 tribes. Out of these 88 species, 50 are new departmental records for Ñeembucú, and one is a new national record for the Paraguayan flora. This work highlights the importance of regular monitoring and constant updating of biodiversity data to support sustainable development in the face of the rapid advancement of agriculture and forestry projects threatening natural ecosystems


INTRODUCTION
Paraguay is a land-locked country between 19°18′-27°03′S and 054°15′-062°38′′W at the heart of the South American continent (Benítez et al. 2023), and lies entirely within the Río de la Plata drainage system, the second largest in South America, behind only the Amazon basin (Rieu-Clarke et al. 2012).The country is divided by the Paraguay River into the Oriental region (also known as the Paraná region) and the Occidental region (also known as the Chaco), which forms part of the Gran Chaco Americano that is shared between Argentina, Bolivia and Paraguay (De Egea et al. 2012).The country is divided into 17 departments, 14 of which lie to the east of the Río Paraguay (De Egea et al. 2012).It is an ecologically unique country, resulting from its location at the convergence of five ecoregions: the Atlantic Forest, the Humid Chaco, the Dry Chaco, the Pantanal, and The Cerrado, all of which contribute to its floristic richness (Huang et al. 2009;Bueno et al. 2017;Peña-Chocarro and De Egea 2018).Spichiger et al. (2011) stated that Paraguay may be viewed as a large and diversified ecotone in South America.
The Department of Ñeembucú has been one of the least explored and documented areas of Paraguay in terms of floristic diversity (De Egea et al. 2012).This is mainly due to the historical difficulties of accessibility to its wild areas, resulting from its flooded terrain and lack of drivable roads (Fogel 2000).Consequently, the heterogeneous vegetation with ecotonal features of Ñeembucú has been largely undervalued against other ecoregions such as the Atlantic Forests, the Cerrados, and the Chaco.A brief overview of botanists and their major explorations carried out in Ñeembucú can be found in De Egea et al. (2012), from the late 19 th century to present.The most recent checklist of the vascular plants of Ñeembucú included 676 taxa, distributed in 100 families and 374 genera (De Egea et al. 2012), demonstrating an interesting floristic richness, but also highlighting the information gaps that still exist.
The Department of Ñeembucú lacks large, protected areas for the conservation of its wetlands and forests.Just over 400 km 2 are under protection, equivalent to only 3.3% of its area, which makes up part of the Ypoá National Park.This park is shared with the Central and Paraguarí departments and was designated a Ramsar Site in 1995, along with the Natural Monuments Laguna Méndez and Sissi (MADES/PNUD 2020).Furthermore, the expanding agricultural frontier, deforestation, and environmental degradation all represent serious threats to the wetlands and forests of Ñeembucú (Yanosky and Salas-Dueñas 2004).In particular, wetlands and other wild areas of Ñeembucú are threatened by artificial drainage systems created with the purpose of gaining areas of productive land (Yanosky and Salas-Dueñas 2004).These areas are dedicated to forestry with exotic trees, and intensive cattle ranching through the implementation of unsustainable practices that require the introduction of non-native grasses, intensive grazing, and uncontrolled burning of pastures; all these activities have caused extensive, negative impact in recent years (Vogt and Mereles 2005).Consequently, the shortage of protected areas and changes in land use, with few alternatives for sustainable production compatible with conservation, threaten biodiversity and the complex ecological systems of Ñeembucú (De Egea et al. 2012), emphasizing the need for better understanding of its natural resources to support conservation initiatives.
Asteraceae is one of the the largest and most dominant families of flowering plants on Earth (Mandel et al. 2019).It comprises about 1,700 genera and ca.25,000 species worldwide, which constitutes approximately 10% of the world's flowering plant diversity (Mandel et al. 2019).This family has widely distributed taxa, found in all continents except Antarctica, and in almost all types of environments (Funk et al. 2009;Palazzesi et al. 2022), although they prefer open areas, meadows, fields, steppes, and only a few have an aquatic or marshy habit or are characteristic of waterlogged soils that tolerate frequent flooding (Soria 2016).In Paraguay, it is one of the largest families, with 149 genera and 539 species recorded so far (Zuloaga et al. 2019).De Egea et al. (2012) listed 37 species of Asteraceae for Ñeembucú, 13 of which were new records for the department, and one was a new record for the country.Asteraceae was also the third most taxon-rich family of the flora of Ñeembucú, after Poaceae and Fabaceae (De Egea et al. 2012).
We sought to answer how much new data has been generated for the flora of Ñeembucú within the last 12 years, since the previous checklist (De Egea et al. 2012).We wanted to evaluate the representativeness of the previous checklist, as well as the information gaps then underlined by the authors.Considering the diversity and ecological importance of the Asteraceae, this study aims to contribute towards the knowledge of the flora of Ñeembucú, focusing on the Asteraceae as a good indicator of its overall floral biodiversity.

STUDY AREA
The Department of Ñeembucú (25°35′-27°20′S and 056°35′-058°40′W) lies in the southwestern quadrant of the Oriental region of Paraguay and covers an approximate area of 12,147 km 2 (Benítez et al. 2023).Ñeembucú is bordered by the Paraguay and Paraná rivers along its west and south boundaries, respectively (DGEEC 2002) (Figure 1).The average annual temperature is between 22° and 23°C, and average annual rainfall is around 1,500 mm (Acevedo et al. 1990).Most of this area is made up of a plain comprised of alluvial sediments from the Quaternary period, with hydromorphic soils formed from the transport of sediment by rivers and streams, and dominated by shallow hydromorphic and alluvial gley types, planosols, or gley humic acids with high organic matter content (Acevedo et al. 1990).
The area is low in elevation and relatively flat; altitudinal range is between 50 and 124 metres above sea level (Fogel 2000).The natural vegetation is characterised by a predominance of grasslands, periodically or permanently flooded wetlands, palm savannahs with Copernicia alba Morong or Butia paraguay ensis (Barb.Rodr.)L.H. Bailey as the dominant palm trees, riparian forests, and semi-deciduous sub-humid forests on islets (Acevedo et al. 1990;Vogt and Mereles 2005;De Egea et al. 2012;Cartes et al. 2016).The Ñeembucú Department belongs to the Ñeembucú Ecoregion of Paraguay (Acevedo et al. 1990; MADES/ PNUD 2020), and it is classified within the biome of tropical and subtropical grasslands, savannahs, and shrublands (Olson et al. 2001) and the Chacoan Province (Cabrera and Willink 1973;Morrone 2014).
As a result of the particular topographic and hydrographic features, Ñeembucú is usually described as an extensive floodplain (Fogel 2000).Over 85% of this area is wetlands (Fogel 2000), where water is the primary factor that regulates seasonal variation and biological and ecological characteristics of the floral composition (Fogel 2000).The wetlands of Ñeembucú are the largest in the Oriental region and are very rich in terms of alpha and beta diversity, particularly when it comes to species of flora and fauna closely linked to water (Vogt and Mereles 2005).
The wetlands and forests of Ñeembucú comprise physical features and species composition similar to the humid Chaco.Thus, they are regarded as intrusions of Chaco vegetation into the Oriental region (Mereles 2004;Vogt and Mereles 2005).However, the sandy layer, which emerges in many parts of the department, results in the development of more diverse and transitional habitats (Mereles 2004).Consequently, the vegetation of Ñeembucú is a mosaic of species typical of both the Eastern and Western (Chaco) regions (Mereles 2004).Spichiger et al. (1995) described the tree flora of Ñeembucú as "a most interesting boundary zone between the Chacoan, the Palm-Savannahs, the Residual Pleistocenic Dry Seasonal, and the Paranean Floras", i.e., an ecotone between dry forests, wet forests, and savannahs.

METHODS
We built the checklist of the Asteraceae of Ñeembucú based on two sources of data: 1) The sampling and collection of Asteraceae species occurring in key sites, selected according to accessibility (availability of roads and entry permissions to private properties issued by the owners), and the presence of several types of vegetation from areas with different conservation status, ranging from wild areas to cattle grazing fields, cropfield surroundings, and suburban areas (Figure 1).Each site was surveyed once.We surveyed a series of random, georeferenced points (up to 8 per day) to collect the plants occurring within a 50 m radius.We carried out intensive sampling in the winter, spring, and summer months of 2022 (August, September, October, November, December); collection of herbarium samples were always made with flowers and/or fruits.Herbarium specimens were dried and deposited in the Facultad de Ciencias Químicas, Universidad Nacional de Asunción, Paraguay (FCQ) (Thiers 2024).Identification of specimens was made with the use of traditional taxonomic methods and the relevant literature available for the country and region (Cabrera 1974;Soria and Zardini 1995;Cabrera et al. 1996;Cabrera and Freire 1998;Cabrera et al. 2009;Soria and Mereles 2022).
We compiled voucher information for each taxa present in Ñeembucú in a spreadsheet database.Taxonomic classification, regarding subfamilial and tribal circumscription, follows The Compositae Global Database (Compositae Working Group 2024).Nomenclatural data follows the International Plant Names Index (IPNI 2024) and accepted names are in line with The Compositae Global Database (Compositae Working Group 2024).
In the checklist, species are sorted alphabetically within tribes, and then alphabetically within subfamilies.For each taxon, we present the accepted name, general distribution in Paraguay by departments (Figure 2), residence status (all species are native except where indicated), global distribution (based on the relevant literature and the revised specimens from the consulted herbaria), and one voucher specimen, specifying the collector's last name and collection number, as well as the herbarium code number or barcode.We provide species-level identification for the newly recorded taxa, based on key characters.

DATA RESOURCES
The data underpinning the checklist reported in this paper were deposited on 27 July 2024 at GBIF, the Global Biodiversity Information Facility, http://ipt.pensoft.net/ipt/resource.do?r=xxxxxx
According to the Asteraceae life forms analysis, about 69% of the species in the checklist are herbs, 11% are subshrubs, 16% are shrubs, and only 3% are vines (Figure 9).Regarding the vegetation types occupied by the taxa documented (Figure 10), most of the species inhabit open vegetation types such as savannahs, grasslands, and prairies (38%) and many of them additionally exploit disturbed areas (17%) such as crop fields, cattle pastures, road edges, farms, urban and suburban areas, and modified soils.About 7% of the species are exclusively associated with forests, and another 13% are adapted to ecotonal conditions such as forest edges and clearings, many of them also present in savannahs and grasslands.Hygrophilous species strictly or closely associated with wetlands make up about 26% of the list.Subfamily Asteroideae (Cass.)Lindl.Tribe Anthemideae Cass.

Distribution in
Global distribution.Tropical and subtropical America; introduced to other continents.
Phenology.Flowers throughout the year.Ecology.Savannahs, grasslands, and prairies.On sandy soils.

DISCUSSION
In this updated list of the Asteraceae of the Ñeembucú Department of Paraguay, we added 50 new records for the department and one new record for the country, all of them resulting from our recent field work.This reinforces the necessity of efforts and financial investments in field-based botanical research in the region and country-wide.This work more than doubles the diversity of Asteraceae for Ñeembucú since the previous checklist (De Egea et al. 2012).
The most species-rich tribes documented here are in line with results of other floristic studies in the country.Eupatorieae is the largest Asteraceae tribe in Paraguay, with the most taxa previously recorded for Ñeembucú (De Egea et al. 2012), for the Asteraceae flora of Paraguayan wetlands (Soria and Mereles 2022), for the flora of the Mbaracayú Forest Nature Reserve (Peña-Chocarro et al. 2010), and even for the endemic flora of Paraguay (Peña-Chocarro and De Egea 2018).The tribes Astereae, Heliantheae and Vernonieae follow the Eupatorieae for species-richness, although the order varies by region.
The predominance of herbs and subshrubs within the Asteraceae taxa of Ñeembucú is in line with the vegetation types they occupy, since this is an area of Paraguay dominated by wetlands, savannahs, and grasslands.
Most of the listed taxa are native to Paraguay, to South America, or display a wide natural distribution within tropical America (85 species).One is an endemic taxon: Tessaria dodoneifolia subsp.plucheoides, which was previously known only from the Departments of Central and Presidente Hayes (Peña-Chocarro and De Egea 2018), but is now also documented in Ñeembucú.This species seems to be restricted to the areas associated with the banks of the Paraguay River.Three species are non-native: Carduus acanthoides subsp.acanthoides, Cirsium vulgare subsp.vulgare and Sonchus oleraceous: all three of which are widely recognised as invasive plants worldwide.Sonchus oleraceous is a well-established species in Paraguay, present throughout most of the territory, and known as a common weed in crop fields, cattle pastures, and disturbed or modified areas in general.The presence of Carduus acanthoides in Paraguay, however, is recorded here for the first time, while the first record of Cirsium vulgare for the country was made by De Egea et al. (2012).These two Cardueae species, native to the Old World and North America, respectively (Susanna and Garcia-Jacas 2009), are also notorious for their invasive, weedy behaviour (Cabrera 1974;Lorenzi 2008), and are naturally associated with temperate climates.Consequently, their first records from the south of Paraguay could indicate an escalating dispersion process of these invasive plants from temperate to subtropical climates.
Asteraceae are well known for their ability to colonize open, recently modified and disturbed areas, to the point of becoming highly problematic weeds.About 17% of the species documented are widespread colonizers, but two of them in particular, Bidens pilosa and Erigeron bonariensis, have been mentioned in the literature as two of the most frequent, abundant, and resistant weeds in Paraguay (De Egea et al. 2016) as well as in other countries of the region (Lorenzi 2008;Guglieri-Caporal et al. 2011;Ferrari 2012).They show great plasticity and resilience, high adaptability to different types of soils and climates, they produce high volumes of biomass and a great number of seeds.
The results of our study emphasize the relevance of carrying out plant expeditions and ongoing monitoring efforts, since, as already pointed out by De Egea et al. (2012), the knowledge of the biodiversity of Ñeembucú is far from complete, not only taking into consideration other ecologically and taxonomically important plant families, but also elements of the fauna, vulnerable ecosystems, and ecological processes.While Ñeembucú is not considered a "hotspot" area for conservation efforts (Dinerstein et al. 1995;Myers et al. 2000), the savannahs, grasslands, prairies, and wetlands of Ñeembucú are unique in terms of biodiversity.Historically, the ecosystems of Ñeembucú have remained in pristine condition until very recently, mainly due to their isolation from the floodable terrain and lack of drivable roads.However; the area is now currently facing a process of increasing habitat loss and land use change due to the expansion of forestry and agricultural activities.It is hoped that this checklist will contribute towards a better knowledge of the Ñeembucú biodiversity, to inspire further studies and the systematization of data, and to prioritise initiatives of national and global biodiversity conservation.

Figure 1 .
Figure 1.Location of the Department of Ñeembucú in Paraguay (red dots indicate sampling points).

Figure 2 .
Figure 2. Political division of Paraguay into 17 departments.

Figure 9 .
Figure 9. Life forms of the Asteraceae species of Ñeembucú (in percentages).

Figure 10 .
Figure 10.Vegetation types occupied by the Asteraceae species of Ñeembucú (in percentages).

Figure 8 .
Figure 8. Tribes of Asteraceae present in Ñeembucú showing number of genera and species.

Table 1 .
List of Asteraceae from the Department of Ñeembucú, Paraguay.New records for the Department are marked with (*) and new records for the country with (u).
Ecology.Riparian forests, palm savannahs, and proximate to wetlands.Phenology.Flowers from September through March.
Global distribution.North, Central and South America.
Phenology.Flowers from August through May.