New record of Serpocaulon triseriale ( Sw . ) A . R . Sm . ( Polypodiaceae ) in Argentina , with morphological comparison of relatives

Serpocaulon triseriale (Sw.) A.R. Sm. is considered the most widespread species in the genus. It has been recorded from south of Mexico to Bolivia, Paraguay and Brazil. Here, we expand its distribution by reporting a new record from Salta province, Argentina, based on material that was previously misidentified as S. polystichum (Link) A.R. Sm. We compare the S. triseriale and S. polystichum with their relatives (S. attenuatum (Humb. & Bonpl. ex Willd.) A.R. Sm., and S. rex Schwartsb. & A.R. Sm.), providing photographs of the plants in the field, SEM images of the spores and light photos of the rhizome scales to discriminate S. rex from S. triseriale. In addition, distributional records are included.


Introduction
Serpocaulon A.R. Sm. (Polypodiaceae) is a tropical American fern genus (Smith et al. 2006), which presents its highest diversity in the Andes of Colombia (Sanín 2018), Bolivia (Smith et al. 2018), and in the Atlantic Rain Forest of Brazil (Labiak and Prado 2008).
There are several recent publications that try to remediate the incomplete and inaccurate knowledge on the distribution of Serpocaulon species.Batke and Hill (2013) expanded the distribution of S. lasiopus (Klotzsch) A.R. Sm., which was previously known from Venezuela to Brazil (Smith et al. 2006), to include Nicaragua to Argentina.More recently, S. latissimum (R.C.Moran & Øllg.)A.R. Sm., which was originally thought by Moran and Øllgaard (1995) to be an Ecuadorian endemic, had its range extended to include Bolivia and Brazil (Sanín 2018, Smith et al. 2018).
An interesting case is Serpocaulon triseriale (Sw.)A.R. Sm. (Fig. 1), the most widely distributed species in the genus (Smith et al. 2006, 2018, Sanín 2018), which is known from southern Mexico to Bolivia, Paraguay, and Brazil (Smith et al. 2006(Smith et al. , 2018) ) but implicitly not known from Argentina.This species remains without a detailed description of its geographical range.In Colombia for example, it is the most abundant species and is recorded in 23 of the 32 Colombian departments (Sanín 2018).Nevertheless, although Smith et al. (2006) recognized its presence in the neighboring countries, S. triseriale had apparently been misidentified as S. polystichum (Link) A.R. Sm. because it is the only species of Serpocaulon with pinnate laminae listed in Flora of Argentina (Cacharani et al. 2014, 2016, Labiak et al. 2008, Flora de Argentina 2018).
After examining Argentine and Brazilian collections of Serpocaulon, we evaluated this possible misidentification and collected data in support that the species recorded in Argentina is not S. polystichum but S. triseriale.Thus, our aims of our study are to present the new record for Argentina, provide novel microcharacters, and compare it with species that could be confused morphologically with S. triseriale, namely S. attenuatum (Humb.& Bonpl.ex Willd.)A.R. Sm. (Sanín 2018) known from neighboring Bolivia, and the recently described S. rex Schwartsb.& A.R. Sm. (Schwartsburd and Smith 2013) from south-central Brazil.

Methods
Collections of Serpocaulon housed at BHCB, COL, CORD, CUVC, FAUC, HNH, HUA, K, LIL, LP, LPB, MCNS, MO, RB, SP, VIC, UPCB, and USM (after Thiers 2018), were examined in full.We focused on the following morphological characters: rhizome scales, laminar dissection, number of pinnae, number of areoles at the middle of the pinna, and number of sori between the costa and the margin.In addition, we carefully studied SEM images of the spores (following Ramírez-Valencia and Sanín 2016), from the type specimen of S. rex (P.B.Schwartsburd & L.M. Alves 2596, VIC), and the Argentine collection (M.Ramos s.n., MCNS), which was misidentified as S. polystichum.Hensen (1990), isotipo BM¡). Figure 1C, D, G, H, J  Identification.We found that the species of Serpocaulon most similar to the single (M.Ramos s.n.) Argentine specimen are S. attenuatum, S. rex, and S. triseriale (Table 1).Those 3 species present short-creeping (except in S. rex), thick rhizomes (5.7-20 mm) with light brown, patent scales and erect leaves that exhibit a protuberant venation in their pinnae, features that could confound them.A comparison of S. triseriale (the putative Argentine pinnate species) with the other 2 species (Table 1) shows that the principal differences are found in the lamina division, with pinnate laminae in S. rex and S. triseriale, and pinnatifid laminae (with few proximal pinnate pinna and distally pinnatifid) in S. attenuatum (Table 1).The Argentine material exhibits a short-creeping rhizome, patent scales, and pinnate laminae.For these key characters, and due to their distribution, we are focusing on comparing Ramos's material, circumscribed as S. triseriale, with S. rex to discriminate the former as a new record in Argentina.

Discussion
The presence of pinnate laminae with proximal pinnae barely adnate and distal pinnae broadly adnate, has been described in the Prodromus of Bolivian Fern Flora (Smith et al. 2018), and the taxonomic revision of Serpocaulon of Colombia (Sanín 2018).In the same way, the spores of S. triseriale have been widely studied (Murillo and Bless 1978, Hensen 1990, Contreras-Duarte et al. 2006, Coelho and Esteves 2011, Ramírez-Valencia et  Besides morphological differences between Serpocaulon attenuatum, S. rex and S. triseriale, their distribution is also important to note.Although S. attenuatum is said to be widely recorded from Nicaragua to Panama, Venezuela, the Guianas, Colombia to Bolivia, and Brazil (Smith et al. 2006), Smith et al. (2018) suggested a narrow distribution (northern South America from the Guianas to Venezuela and Bolivia).Serpocaulon triseriale also presents a wide distribution from Mexico to Paraguay (Smith et al. 2006), but differs with the former by its higher altitudinal range, recorded in Colombia from the sea level to 2500 m (Sanín 2018), in contrast to S. attenuatum, which is recorded mainly in lowland areas (Sanín obs. pers.).
The record of S. triseriale in Argentina was expected, due to the existence of the corridor represented by the Yungas montane forest.This band of forest occupies the eastern slope of the Andes, between 500 and 3500 m, and goes from Peru to northwestern Argentina (Morrone 2017) and allows for the interconnection of the central and southern Andes (Nores and Cerana 1990).
Serpocaulon rex is endemic to Brazil and has only been recorded in Minas Gerais and São Paulo states, although it might also occur in Mato Grosso do Sul and Goiás (Schwartsburd and Smith 2013).Here, we can confirm that the geographic range of this species does include Mato Grosso do Sul and Goiás.
We also confirm the wide distribution of S. triseriale (Smith et al. 2006, 2018, Sanín 2018), and increase its distribution to include Salta province in Argentina, which is the southernmost record of this species.Altogether, our findings support the construction of an accurate biogeographical hypothesis for Serpocaulon species, their distributional range, and their conservation.

Table 1 .
Comparison between related species of Serpocaulon.