Spiranthinae (Orchidaceae - Cranichideae) from Uruguay: taxonomy and distribution

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Spiranthinae (member of Orchidoideae), with ca.40 genera and 520 species, is the most diverse group of terrestrial orchids in the Neotropics (Garay 1982;Salazar 2003).It is currently considered monophyletic and included within the tribe Cranichideae (Cribb 1999;Salazar 2003;Salazar et al. 2018).It can be distinguished mainly by its tubular and resupinate flowers with lip margins adnate to the sides of the column (Dressler 1993;Pridgeon et al. 2003;Salazar et al. 2018).The subtribe includes ca.33 % of the genera (6 genera) and ca.41 % of the species (24 spp.) of Orchidaceae in Uruguay (Marín-Pérez et al. 2020).Regionally, its representatives comprise ca.35 % of the orchids in the grassland region of the River Plate, which also includes portions of Argentina and Brazil, being the largest continuous grassland region of the Americas (Izaguirre 2010;Schinini 2010;Andrade et al. 2018).
The Southern Cone and Southeast region of Brazil constitute one of the centers of diversity of Spiranthinae (Balogh 1982;Dressler 1993).However, the region of the River Plate Grassland has been historically neglected for conservation mainly due to interest in the high agricultural productivity of the region (Foley et al. 2011;Andrade et al. 2018;Bilenca et al. 2018).In this area 35 species of Orchidaceae have been classified as a priority for conservation, of which 10 are members of Spiranthinae (Marchesi et al. 2013;Marín-Pérez et al. 2020).
Although a list of the species of Spiranthinae from Uruguay has recently been published (Marín-Pérez et al. 2020), identification of the species is still challenging for non-specialists due to the lack of taxonomic treatments.Thus, the aim of this study is to provide a detailed study of the Spiranthinae species from the country, including descriptions, illustrations, an identification key and comments on the geographical distribution of the species.

Materials and methods
Uruguay is located in the Southern Cone of South America.It is divided into 19 departments and it has coastlines along the River Plate and the Atlantic Ocean (MVOTMA 2020) (Fig. 1).The country occupies a transitional area, greatly influenced by the Paranaense and Chaqueña provinces (Cabrera & Willink 1973;Morrone 2001;Grela 2004), but it is fully within the River Plate Grassland ecosystem.It is mainly composed of grasslands (G), which occupy 88 % of the territory, and forests, representing 5.2 % of the territory (FAO et al. 2015).The territory has been divided into seven ecoregions with diverse environments, as shown in Figures 1, 2 (Evia & Gudynas 2000;Rivas 2010;Panario et al. 2011;Brazeiro et al. 2012).
The assessment of priority for conservation in the country follows the criteria for vascular plants of Marchesi et al. (2013) and is mentioned in the relevant species.The species considered rare follow criterion 2 of Marchesi et al. (2013): species with few (5) collections (< 5) in Uruguay and without population records.The morphology follows Dressler (1993), Harris & Harris (1994) and Gonçalves & Lorenzi (2007).

Results and Discussion
Spiranthinae is represented in Uruguay by 22 species and seven genera, which corresponds to 45 % of the species of terrestrial orchids in the country (based in Marín-Pérez et al. 2020).The genera Cyclopogon (8 spp.), Skeptrostachys (5 spp.), and Brachystele (4 spp.) were the most representative.
The greatest species richness was found in the "Graben de la Laguna Merín" (14 spp.) (mainly in the departments along the Atlantic Ocean coast), which is one of the regions with the greatest richness of woody and epiphytic species in the country (Brazeiro 2015;Mai 2014).High species richness, though with less significant representation, was also found in the "Sierras del Este" (11 spp.) (Maldonado, Rocha and Lavalleja) and "Cuenca Sedimentaria Gondwánica" (11 spp.) (mainly in Cerro Largo, Rivera and Tacuarembo) (Fig. 2).Among the environments, Spiranthinae was found mainly in the "Serrano forests" (17 spp., 5 genera) and in the coastal forests (12 spp.).Its species occupy the highest altitude areas in the Southeast (Lavalleja, 10 spp.) and Northeast (Rivera,11 spp.,Tacuarembó,9 spp.) regions of Uruguay.It was also found, with less widespread distribution, along the Atlantic Ocean coast in the Southeast (Maldonado,10 spp.,Rocha,12 spp.).This higher richness found in the "Serrano forests" of the "Sierras del Este" (Fig. 1) may be in part a result of dispersal of species from the neighboring provinces (Paranaense and Chaco) (Grela & Brussa 2003).The altitude and constant humidity (due to high temperatures and fog banks) favor the presence of biological corridors and the expansion of the distributional range of groups (Grela & Brussa 2003;Mai 2014).
Grasslands (10 spp., 5 genera), Riparian forests (10 spp.) and "Quebradas forests" (9 spp., 4 genera) also have considerable species richness.The grasslands of the North region may be favored by the practice of grazing and seasonal agriculture.These activities are considered less harmful to the maintenance of diversity (García et al. 2019;Gonçalves 2016;Dostálek & Frantik 2008).The "Quebradas forests" stand out for their peculiar characteristic of forming different microclimates between the top and bottom of ravines (Rivas 2010).
The environments with less species richness and diversity were the following: "parque forests" (6 spp.), wetlands (3 spp.) and "palmares" (1 sp.).These occupy restricted areas in the country (Evia & Gudynas 2000) and are threatened by rice cultivation and overgrazing (Rivas 2010).In "parque forests" in the West and Southwest (Fig. 1) regions, urban expansion associated with the capital of the country and productive activities (agriculture and timber afforestation) were possible causes of the lower species richness (Mai 2014;Achkar et al. 2015;Haretche et al. 2012).Agricultural activities characterized by seasonal crop rotations use herbicides and fertilizers.These strongly impact populations of endemic species in the region (Achkar et al. 2015;MGAP 2015;Schrag et al. 2009).
For the country, eight species were newly classified as conservation priorities according to criteria 1, 2 and 3 of Marchesi et al. (2013).Together with the other previously listed species (Marchesi et al. 2013;Marín-Pérez et al. 2020) 82 % are included, and only four Spiranthinae species (Brachytele camporum, B. dilatata, Cyclopogon apricus and C. elegans) are not conservation priorities in Uruguay because of their wider distribution.
Some species are known from only a few old records and have not been collected recently (Cyclopogon apricus (1986), C. congestus (1987), Cyclopogon taquaremboensis (1933), Skeptrostachys berroana (1972)).Most of these old collections were carried out in environments which are currently urbanized (South region of the country) during a period of intensive collection effort (Mai 2014).It is possible that some of these have become extinct in the country.Nevertheless, the border region with Brazil has habitats suitable for Cyclopogon species, yet this area remains poorly collected.
Although Cyclopogon taquaremboensis and Pachygenium arechavaletae are considered native species in the country, they were not described due to insufficient data (no records in herbaria) for the analysis.For these two species we included the original diagnosis provided by the authors in the protologue.
Phenology-Observed in flower and fruit from November to April.
Notes-This species could be confused with B. dilatata but it differs by the color of the flowers (white-greenish vs. yellow-greenish), shape and length of the lip (oblate, 0.2-0.25 long vs. sub-orbicular to reniform, 0.45-0.5 long).It is considered a priority species for conservation for the country according to the criteria of Marchesi et al. (2013), as it is an endemic species of the Uruguay river basin and has a restricted distribution in Uruguay (criteria 1 and 3).Habitat-In Uruguay it is common and occurs in stony soils of grasslands, the "Serrano forest", and riparian forests.Specimens were also collected in "Cuenca Sedimentaria del Oeste", "Cuenca Sedimentaria Gondwánica", "Graben de Santa Lucía", "Graben de la Laguna Merín", "Escudo Cristalino" and "Sierras del Este" (Fig. 4).
Phenology-Observed in flower and fruit between November and June.
Notes-The shape of the lip and especially the epichile is fairly variable in this species, which, especially when it is rounded at the apex, can generate confusion when compared to B. dilatate.However, these two species can be distinguished by the length and shape of the hypochile (obovate, 0.2-0.3 vs. sub-orbicular to reniform, 0.4-0.7 cm long).Distribution-Argentina, Brazil, Paraguay, Uruguay (Salto).
Habitat-In Uruguay it is rare and occurs in stony soils of "Serrano forest".Present in "Cuenca Sedimentaria del Oeste" (Fig. 4).
Phenology-Observed in flower and fruit from December to February.
Notes-This species could be confused with B. dilatata due to the yellow-greenish flowers, but it differs in the number of number of flowers in the inflorescences (10-15-flowered vs. 50-80-flowered) and in the size of the epichile (0.05 × 0.05 vs. 0.1 × 0.1 cm).It has a restricted distribution in Uruguay meeting criterion 3 of Marchesi et al. (2013), thus it is considered a priority species for conservation for the country.Habitat -In Uruguay it is common and occurs in stony soils of grasslands, "Serrano forest" and riparian forest.Also in "Cuenca Sedimentaria del Oeste", "Cuenca Sedimentaria Gondwánica", "Graben de Santa Lucía", "Graben de la Laguna Merín", "Escudo Cristalino" and "Sierras del Este" (Fig. 4).
Phenology -Observed in flower and fruit between December and February.
Notes -It can be distinguished from the other species of the genus in the country by the larger sub-orbicular to the reniform hypochile (0.4-0.45 × 0.35-0.4 cm).After analysis of the protolog, photo of the holotype and illustration of B. waldemarii (Szlachetko 1996) we propose its synonymization under B. dilatata.Brachystele waldemarii is known only by the type specimen collected in 1918.The characters used to support it as distinct from B. dilatata (non-auriculate, rhomboid and sessile lip, transversely elliptical epichile, petals linear and falcate, lateral sepals falcate and 3-nerved) can be observed in specimens of B. dilatata, thus these characters are understood as part of its morphological variation.
Phenology-Observed in flower and fruit from September to March.
Phenology-Observed in flower and fruit in September and October.
Notes-It could be confused with C. elegans but differs by the shape and length of the hypochile (ovate-oblong, 0.25-0.3cm vs. oblong, 0.4-0.5 cm long).It is considered a priority species for conservation for the country according to the criteria of Marchesi et al. (2013), due to its restricted distribution in Uruguay (criterion 3).
Phenology-Observed in flower and fruit in October and November.Habitat-In Uruguay it is rare and occurs in stony and sandy soils of grasslands, "Serrano Forest", and "Quebradas forest".Present in "Cuenca Sedimentaria Gondwánica", "Sierras del Este" and "Cuesta Basáltica" (Fig. 9).
Phenology-Observed in flower and fruit from January to March.
Notes-The species could be confused with S. gigantea but differs by the length and shape of the petals (ovateelliptical, 0.7-1.0 vs. lanceolate, 1.1-1.2cm long), and the length of the epichile (0.3-0.4 vs. 0.5-0.6 cm long).
Habitat-In Uruguay it is rare and occurs in stony soils of grasslands, and "Serrano forest".Present in "Graben de la Laguna Merín" and "Sierras del Este" (Fig. 9).
Phenology-Observed in flower and fruit in January and February.
Notes-The species could be confused with S. gigantea but differs by the length of the peduncle (20-60 vs. 80-150 cm long) and width of the lip (0.7-0.75 vs. 0.8-0.9cm wide).It is a rare species, endemic in Uruguay, and presents a restricted distribution in Uruguay, meeting criteria 1, 2 and 3 of Marchesi et al. (2013).
Phenology-Observed in flower and fruit between December and April.
Notes-It is easy to recognize among the species of the genus in the country by the longer peduncle (80-150 cm long).
Phenology-Observed in flower and fruit between March and June.
Notes-It could be confused with S. berroana but it is easy to distinguished by the color of the flowers (white-pinkish vs. white-greenish), the shape of the petals (elliptical vs. lanceolate), and the length of the lip (0.8-0.95 vs. 1.2-1.3).It is considered a priority species for conservation for the country according to the criteria of Marchesi et al. (2013) for having a restricted distribution in Uruguay (criterion 3).

Figure 4 .
Figure 4. Distribution of species of Brachystele in relation to the relief of the country.

Figure 5 .
Figure 5. Distribution of species of Cyclopogon in relation to the relief of the country.

Notes-
It differs from the other Spiranthinae of Uruguay by the linear-oblong shape and the larger size (1.7-2.1 × 0.4-0.6 cm) of the lip and the red to red-orangish flowers.It has a restricted distribution in Uruguay, meeting criterion 3 of Marchesi et al. (2013), thus it is considered a priority species for conservation for the country.

Figure 8 .
Figure 8. Distribution of species of Pachygenium, Pelexia and Sacoila in relation to the relief of the country.

Figure 10 .
Figure 10.Spiranthinae from Uruguay.A-B.Pachygenium bonariense. A. Detail of the flowers.B. Specimens in the habitat.C-D.Sacoila lanceolata.C. Detail of the flowers, D. Specimens in the habitat.E-F.Skeptrostachys arechavaletanii.E. Detail of the flowers, F. Specimens in the habitat.G-H.Skeptrostachys balanophorostachya.G. Detail of the Flowers, H. Specimens in the habitat.I-J.Skeptrostachys gigantea.I. Detail of the flowers, J. Specimens in the habitat.K-L.Skeptrostachys paraguayensis.K. Detail of the Flowers.L. Specimens in the habitat.