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Acta Botanica Brasilica

Print version ISSN 0102-3306On-line version ISSN 1677-941X

Acta Bot. Bras. vol.30 no.2 Belo Horizonte Apr./June 2016  Epub Apr 19, 2016

http://dx.doi.org/10.1590/0102-33062016abb0058 

Articles

Distribution patterns of ferns and lycophytes in the Coastal Region of the state of Rio Grande do Sul, Brazil

Felipe Gonzatti1  * 

Letícia Machado2 

Paulo Günter Windisch2 

1 Herbário da Universidade de Caxias do Sul, Universidade de Caxias do Sul, Rua Francisco Getúlio Vargas 1130, 95020-972, Caxias do Sul, RS, Brazil

2 Programa de Pós-graduação em Botânica, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, 91501-970, Porto Alegre, RS, Brazil

ABSTRACT

A survey of ferns and lycophytes of the Coastal Region of the state of Rio Grande do Sul (CRRS) was performed based on field work and collections of the main regional herbaria. The following were evaluated for each species: preferential habits (terrestrial, epiphytic or aquatic), geographic distribution patterns and habitats (forest, grassland, and wetland). The occurrence of a latitudinal gradient in diversity was tested over five latitudinal ranges using the Sørensen Similarity Index. A total of 17 lycophyte and 206 fern species representing 28 families was found between the latitudes of 29° and 34°S. Exclusively terrestrial species were predominant (162), with the majority (113) exhibiting wide Neotropical distributions, followed by species that also occurred in the state of Paraná (44). The forest habitat harbored the greatest number of species (159), while grasslands had the fewest (26). Cluster analysis showed pronounced floristic differentiation among latitudinal Ranges III (31°01' to 32°S) and IV (32°01' to 31°S), with a similarity index of only 0.41. Our results demonstrate a strong north-to-south reduction in species richness in the study area, which is related to environmental conditions along the latitudinal gradient and, especially, microclimatic differences in the transition zone between the Atlantic Forest and Pampa biomes.

Keywords coastal vegetation; ecology; floristic diversity; latitudinal gradient; phytogeography

Introduction

Ferns and lycophytes are significant components of tropical and temperate floras, occupying a variety of ecological niches (Holttum 1938; Tryon & Tryon 1982; Windisch 1992; 1996; 2002; Page 2002; Sharpe et al. 2010), and having patterns of geographical distribution that are associated with the long distance dispersal capacity of their spores (Tryon 1970; Smith 1972; Barrington 1993; Wolf et al. 2001).

In the meridional portion of South America (the "Southern Cone"), centers of species diversity and endemism, as well as limits to floristic distributions, have been related to paleogeographical alterations that produced climatic barriers and interrupted floristic continuity (Sota 1973; Ponce et al. 2002). At a local scale, climatic factors, such as temperature and humidity (Kessler 2001; Kessler et al. 2011), variation in the chemical composition of the edaphic matrix (Tuomisto & Ruokolainen 1993; Tuomisto & Poulsen 1996; Tuomisto et al. 2003a; Tuomisto et al. 2003b; Tuomisto et al. 2014), variation in pH (Ranal 1995a), environmental heterogeneity (Sylvestre & Windisch 2003; Dittrich et al. 2005; Nettesheim et al. 2014), and fragmentation and edge effect (Paciencia & Prado 2005) have been implicated in determining fern and lycophyte distribution.

There are about 140 lycophyte and 1,100 fern species in Brazil (Prado & Sylvestre 2015), with the greatest number occurring in the montane regions of the Atlantic Forest biome (Windisch 2002; Dittrich et al. 2005; Prado & Labiak 2009). The presence of a center of diversity and endemism of ferns and lycophytes in the Atlantic Forest of southeastern Brazil (Tryon 1972), is relevant for the diversity of southern Brazil, including the Coastal Region of the state of Rio Grande do Sul. This diversity within Rio Grande do Sul is represented by approximately 397 species (Sehnem 1977), mainly known from regional surveys (Mondin & Silveira 1989; Bueno & Senna 1992; Senna & Waechter 1997; Athayde-Filho & Windisch 2006; Schmitt et al. 2006; Lehn et al. 2009; Santos & Windisch 2008 Schmitt & Goetz 2010; Becker et al. 2013; Silva et al. 2013; Gonzatti et al. 2014a; Gonzatti et al. 2014b; Mallmann & Schmitt 2014), phytogeographic and palynological reviews (Sehnem 1977; Lorscheitter et al. 1998; 1999; 2001; 2002; 2005; 2009), and research on ecology, phenology and development (Schmitt & Windisch 2010; Schneider & Schmitt 2011; Schmitt & Windisch 2012; Rocha et al. 2013; Neumann et al. 2014; Quevedo et al. 2014; among others).

The Coastal Region possesses distinct phases of vegetational succession, featuring a mosaic of floristic communities from open grassland and wet areas to arboreal communities (Waechter 1990; Waechter & Jarenkow 1998; Müller & Waechter 2001). This mosaic is determined mainly by edaphic conditions, but also by wind action and extreme insolation (Rambo 1956). However, there is general transition in vegetation cover from it being scarce and sparse at the coastline, to gradually giving rise to forests with tropical characteristics in the continental interior (Rambo 1951; 1954; Klein 1984; Waechter 1990).

A marked change in vegetation cover is mainly determined by climatic changes close to the 30° S parallel, where abrupt differences in rainfall and temperature regimes occur, resulting in a north-to-south reduction of species richness, especially with regard to tropical elements (Rambo 1951; Waechter 1990). This north-to-south change from a tropical to a temperate climate induces floristic changes including the substitution of the Atlantic Forest biome by the Pampa biome in this portion of Rio Grande do Sul (Waechter 1985; Fiaschi & Pirani 2009; Overbeck et al. 2012).

Considering that only about 15% of the original Coastal Region vegetation coverage remains (Cordeiro & Hasenack 2012), and that area is a priority for conservation for the state of Rio Grande do Sul (MMA 2000), an increase in the knowledge of flora in this transitional vegetation formation would be valuable. Through this inventory, we seek to understand the distribution patterns of ferns and lycophytes among different vegetation physiognomies and along a latitudinal gradient in the study area, and the relationships of these plants with adjacent plant communities.

Materials and methods

Study area

The study area comprises the entire Coastal Region of the state of Rio Grande do Sul (CRRS hereafter), situated between the latitudes of 29°17'S to 33°41'S and the longitudes of 49°43'W to 53°31'W. The area encompasses about 33,000 km², and is characterized by extensive lowlands and several shallow freshwater lakes (Fig. 1), extending from the municipality of Torres in the north, to Chuí in the south. The CRRS is limited to the west, continental, side by the geomorphological formations of the "Sulriograndense" Plateau (a.k.a. "Serra Geral"), to the north, by the Central Depression and by the Sulriograndense Shield to the south. The origin of the Coastal Region is discussed by Tomazelli et al. (2000), Villwock & Tomazelli (2007) and Buchmann et al. (2009).

Figure 1 Location of the Coastal Region of Rio Grande do Sul, highlighting the sampled localities and the five latitudinal ranges (I: 29°17'-30°S, II: 30°01'-31°, III: 31º01'- 32ºS, IV: 32º01' - 33ºS, V: 33°01'-33°41'S). 

Despite the relative uniformity of these coastal areas, microtopographic variation allows for two main soil types: well drained sandy soils at low elevations, and poorly drained sandy, clayish or peaty soils in the lowlands. Most of the terrain is covered by Solodic Planosol derived from alluvial and lacustrine depositions or sandstone decomposition. These Planosol areas are poorly drained and have low fertility, with forest growing on peat. The northern portion is characterized by Hydromorphic Humic Quartz-Soil type (Neosol) of sedimentary origin formed during the Holocene and featuring a high accumulated-carbon content and poor drainage. Also in the northern portion, shallow and highly fertile Chernosols are present, with rock mixtures in the A horizon. Red Latosol can also be found, constituting deep soils, rich in iron and nutrient poor in the A horizon. Dune banks of depositional origin prevail along the coastline, composed of quartz sands of low pedogenetic structuration, low fertility and high wind mobility (Moser 1990; Embrapa 2006).

According to the Köppen classification, the climate is Cfa type, subtropical with hot summers with the coldest monthly mean temperature higher than −3 °C and the warmest above 22 °C, with an annual average of around 17.6ºC. Monthly precipitation varies between 100 and 170 mm, heterogeneously distributed between the extreme north and south of the Coastal Region (annual average: 1,423 mm in Torres and 1,186 and in Santa Vitória do Palmar). These climate conditions occur in most regions with altitudes below 600-650 m alt., and cover all the Coastal Region, reaching the limit at the Cfb climate type being found at the highest elevations (Moreno 1961; Alvares et al. 2013).

Sampling and data processing

Field work was conducted between March 2013 and December 2014 in 19 municipalities (Fig. 1). Spot inventories were conducted in different vegetation formations with random sampling following the procedure described by Filgueiras et al. (1994), from the seaside and up to 50 m alt. in regions with slope. The samples were collected and preserved following Windisch (1992). Voucher specimens were deposited in the ICN and HUCS herbaria (acronyms based on Thiers 2015).

Collections of the following herbaria were reviewed: Herbário do Instituto de Ciências Naturais, Universidade Federal do Rio Grande do Sul (ICN), Instituto Anchietano de Pesquisas, Universidade do Vale do Rio dos Sinos (PACA), Herbário Alarich Schultz, Fundação Zoobotânica do RS (HAS), Herbário da Universidade de Caxias do Sul (HUCS), Herbário da Universidade Federal de Pelotas (PEL) and Herbário da Universidade Federal de Rio Grande (HURG). All exsiccates from the study area were annotated with updated identifications and nomenclature, and their location and habitat information were added to our database.

The taxonomic delimitation of families and genera follows Smith et al. (2008), with the genus Deparia Hook. & Grev. belonging in Athyriaceae (Rothfels et al. 2012). Adaptations to Lycopodiaceae followed Øllgaard (2012). For the genus Blechnum L. we followed Perrie et al. (2014). For Tryonia J. Prado, A. T. Cochran we followed Cochran et al. (2014), and for Mickelia R. C. Moran et al. we followed Moran et al. (2010). Abbreviations of the names of the authors of species follow the Species List of the Flora of Brazil (Prado & Sylvestre 2015).

Species habits were categorized as terrestrial, epiphytic or aquatic and assigned to habitats: forest, grassland, wetland or combinations thereof. Species distribution patterns were categorized based on Waechter (2002) and Cabrera & Willink (1980), as follows:

Global distribution:

Cosmopolitan: widely distributed across the five continents;

Amphipacific: disjunct distribution in the tropical and subtropical regions of America and Asia;

Holarctic: wide distribution in the temperate regions of the Northern Hemisphere and Eurasian region;

Pantropical: distribution in the American, African and Asian tropical regions;

Neotropical: distribution restricted to the American tropical and subtropical region;

Neotropical distribution:

Neotropical-Antarctic: distribution in the Neotropical region, with eventual occurrence in temperate South-American regions;

Neotropical-Atlantic: restricted to the Atlantic province;

Neotropical-Paranaense: restricted to the Paranaense province;

Neotropical-Pampeana: restricted to the Pampa biome.

The latitudinal distributions of the taxa within the study area were verified by their presence or absence in five latitudinal ranges, according to Waechter (1998). In this study, Ranges I and V were smaller than Ranges II, III and IV, as only areas within the state of Rio Grande do Sul were evaluated, and did not extend into the state of Santa Catarina or Uruguay (Fig. 1).

Range I (extreme North): species occurring from 29°17' south to 30ºS;

Range II (North): species occurring between the parallels 30º01' and 31ºS

Range III (Middle center): species occurring between the parallels 31°01' and 32°S;

Range IV (South): species occurring between the parallels 32°01' and 33°S;

Range V (extreme South): species occurring beside the parallel 33°01' and 33º41'S.

The floristic similarity among distinct latitudinal ranges was evaluated by applying the Sørensen Similarity Index using the Unweighted Pair-Group Method with Arithmetic Logarithm (UPGMA). This analysis was processed by the Past 3.04 software (Hammer et al. 2001).

Results

A total of 3,450 herbarium records were evaluated, including 520 collected during our field work and 2,930 previously existing in collections. In total the records represented 223 species in 79 genera and 28 families, of which 17 were species of lycophytes and 206 were species of ferns (Tab. 1).

The largest values for species richness were for the families: Pteridaceae (34), Polypodiaceae (29), Thelypteridaceae (23), Dryopteridaceae (22), Aspleniaceae (18) and Blechnaceae (13). Marattiaceae, Psilotaceae, Lygodiaceae, Isoetaceae and Equisetaceae had one species each (Tab. 1). The genera with the largest values for species richness were: Thelypteris (22), Asplenium (17), Blechnum (12), Elaphoglossum (nine), Pecluma (eight), Pleopeltis (seven) and Doryopteris (seven), with the remaining genera varying from one to six species (Tab. 1).

Richness differed among the evaluated latitudinal ranges, with the number of taxa gradually decreasing from north-to-south with Range I having 198 species, while Range V had only 28. Of the total 223 species, only 21 occurred throughout the entire study area (Tab. 1). Large reductions in floristic richness occurred between latitudinal Ranges III and IV, and between Ranges IV and V, with a decrease of 46% and 51%, respectively. A 43 % reduction in floristic richness was observed between Ranges I and II. At the northern extreme of the study area (Range I), 34% of the richness corresponded to species that occur exclusively in that portion of the area, while in ranges to the south exclusive species comprised less than 10%, reaching 0% in the extreme South (Range V) (Fig. 2).

Figure 2 Species richness for ferns and lycophytes found in each latitudinal range sampled. 

Table 1 Floristic composition found in the Coastal Region of Rio Grande do Sul. Families, Species, Habit: T - terrestrial; E - epiphyte ; A - aquatic. Vegetation: F - forest; G - grassland; W - wet land. Geographic distribution pattern: COS - cosmopolitan; PAN - pantropical; HOL - holarctic; ANP - anfipacific; NEO -neotropical; NEO-ATL - neotropical-atlantic; NEO-PAR - neotropical-paranaense; NEO-PAM - neotropical-pampeana; NEO-ANT - neotropical-antarctic. Latitudinal occurrence: I - 29°17'-30°S; II - 30°01'-31°; III - 31º01'-32ºS; IV - 32º01'-33ºS; V - 33°01'-33°41' of South latitude. Herbarium voucher: reference material deposited in the herbaria ICN, HAS, PACA, HUCS e HURG. 

Families/Species Habit Habitat Geographic pattern Latitudinal occurrence Herbarium voucher
ANEMIACEAE
Anemia ferruginea Humb. & Bonpl. ex Kunth T F NEO I PACA 100902
Anemia phyllitidis (L.) Sw. T F NEO I, II, III, IV HUCS 41492
Anemia tomentosa (Sav.) Sw. T G/F NEO I, II, III, V HUCS 41507
Anemia warmingii Prantl T F NEO-ATL I ICN 107595
ASPLENIACEAE
Asplenium abscissum Willd. T F NEO I, III ICN 171238
Asplenium bradei Rosenst. T F NEO-ATL I, II HUCS 41361
Asplenium brasiliense Sw. T F NEO-PAR I, II ICN 161392
Asplenium claussenii Hieron. T F NEO I, II, III, IV ICN 176197
Asplenium gastonis Fée T/E F NEO-PAR I, II, III, IV HUCS 41374
Asplenium harpeodes Kunze T F NEO I, II ICN 171237
Asplenium inaequilaterale Willd. T F PAN I, II, III HUCS 41399
Asplenium incurvatum Fée E F NEO-ATL I, II PACA 72760
Asplenium kunzeanum Klotzsch ex Rosenst. T F NEO-ATL I ICN 176481
Asplenium martianum C. Chr. T F NEO-ATL I ICN 176746
Asplenium mucronatum C.Presl E F NEO-PAR I HUCS 40582
Asplenium oligophyllum Kaulf. T F NEO I ICN 171106
Asplenium scandicinum Kaulf. E F NEO-PAR I, II, III HUCS 39487
Asplenium sellowianum (Hieron.) Hieron. T F NEO-PAR I, II, III, IV, V HUCS 41134
Asplenium serra Langsd. & Fisch. T F NEO I, II, III ICN 161365
Asplenium ulbrichtii Rosenst. T F NEO-PAR II, III, V HUCS 41523
Asplenium uniseriale Raddi T F NEO I ICN 124310
Hymenasplenium triquetrum (N. Murak. & R.C. Moran) L. Regalado & Prada T F NEO I ICN 124318
ATHYRIACEAE
Deparia petersenii (Kunze) M. Kato T F ANP I, II, III, V HUCS 41400
Diplazium ambiguum Raddi T F NEO I ICN 126284
Diplazium cristatum (Desr.) Alston T F NEO I, II, III ICN 176745
Diplazium herbaceum Fée T F NEO-ATL I, II ICN 107001
Diplazium plantaginifolium (L.) Urb. T F NEO I, II ICN 161430
BLECHNACEAE
Blechnum acutum (Desv.) Mett. T/E F NEO I, II, III, IV HUCS 41401
Blechnum auriculatum Cav. T F NEO-PAR I, II, III, IV, V HUCS 41084
Blechnum austrobrasilianum de la Sota T F NEO-PAR I, II, III, IV HUCS 41067
Blechnum brasiliense Desv. T F/W NEO I, II, III, IV, V HUCS 41069
Blechnum cordatum (Desv.) Hieron. T G/F/W NEO-ANT I, II, III, IV, V HUCS 41055
Blechnum gracile Kaulf. T F NEO I ICN 173499
Blechnum laevigatum Cav. T G NEO-PAR I, II, III ICN 170402
Blechnum lehmannii Hieron. T F NEO I ICN 114698
Blechnum occidentale L. T F NEO I, II, III, IV ICN 176486
Blechnum polypodioides Raddi T G NEO I, II, III HUCS 38878
Blechnum schomburgkii (Klotzsch) C. Chr. T G/W NEO I, II, III HUCS 37970
Blechnum spannagelii Rosenst. T W NEO-ATL I, II ICN 172982
Telmatoblechnum serrulatum (Rich.) Perrie, D.J. Ohlsen & Brownsey T G/F/W NEO I, II, III, IV, V HUCS 37962
CYATHEACEAE
Alsophila setosa Kaulf. T F NEO-PAR I, II, III ICN 176724
Cyathea atrovirens (Langsd. & Fisch.) Domin T F NEO-PAR I, II, III, IV ICN 176726
Cyathea corcovadensis (Raddi) Domin T F NEO-ATL I HUCS 41403
Cyathea delgadii Sternb. T F NEO I, II HUCS 39883
Cyathea phalerata Mart. T F NEO-ATL I ICN 176725
DENNSTAEDTIACEAE
Dennstaedtia dissecta T. Moore T F NEO I HUCS 41285
Dennstaedtia globulifera (Poir.) Hieron. T F NEO I, IV HUCS 41521
Dennstaedtia obtusifolia (Willd.) T. Moore T F NEO I PACA 77670
Hypolepis acantha Schwartsb. T F NEO-ATL III -
Hypolepis stolonifera Fée T F NEO-ATL III HUCS 41535
Pteridium arachnoideum (Kaulf.) Maxon T G NEO I, II, III, IV, V HUCS 41078
DICKSONIACEAE
Dicksonia sellowiana Hook. T F NEO I, II, III HUCS 41394
Lophosoria quadripinnata (J.F. Gmel.) C. Chr. T G/F NEO-ANT I ICN 176734
DRYOPTERIDACEAE
Ctenitis falciculata (Raddi) Ching T F NEO I HUCS 41548
Ctenitis submarginalis (Langsd. & Fisch.) Ching T F NEO I, II, III HUCS 41310
Didymochlaena truncatula (Sw.) J. Sm. T F PAN I, II HUCS 161411
Elaphoglossum burchellii (Baker) C. Chr. T/E F NEO I ICN 126301
Elaphoglossum glaziovii (Fée) Brade T/E F NEO-ATL I HUCS 41537
Elaphoglossum lingua (C. Presl) Brack. E F NEO-ATL I ICN 172999
Elaphoglossum luridum (Fée) Christ T/E F NEO I HUCS 41538
Elaphoglossum macahense (Fée) Rosenst. T/E F NEO-ATL I PACA 79232
Elaphoglossum macrophyllum (Mett. ex Kuhn) Christ T F NEO-ATL I ICN 51347
Elaphoglossum pachydermum (Fée) T. Moore T F NEO-ATL I ICN 126307
Elaphoglossum scolopendrifolium (Raddi) J. Sm. T/E F NEO-ATL I, II ICN 166160
Elaphoglossum vagans (Mett.) Hieron. T/E F NEO-ATL I ICN 166343
Lastreopsis amplissima (C. Presl) Tindale T F NEO I, II, III ICN 176493
Lastreopsis effusa (Sw.) Tindale T F NEO I, II ICN 161394
Megalastrum abundans (Rosenst.) A.R. Sm. & R.C. Moran T F NEO-ATL I ICN 126310
Megalastrum connexum (Kaulf.) A.R. Sm. & R.C. Moran T F NEO-PAR I, II, III, IV HUCS 41520
Megalastrum oreocharis (Sehnem) Salino & Ponce T F NEO-PAR I ICN 126282
Mickelia scandens (Raddi) R.C.Moran et al. T/E F NEO-ATL I HUCS 41289
Olfersia cervina (L.) Kunze T/E F NEO I ICN 126305
Polybotrya cylindrica Kaulf. T/E F NEO-ATL I, II, III ICN 176730
Polystichum platyphyllum (Willd.) C. Presl T F NEO I, II ICN 107475
Rumohra adiantiformis (G. Forst.) Ching T G/F/W PAN I, II, III, IV, V HUCS 41080
EQUISETACEAE
Equisetum giganteum L. T G/F/W NEO-ANT I, II, III, IV, V HUCS 41128
GLEICHENIACEAE
Dicranopteris flexuosa (Schrad.) Underw. T G NEO I, II, III HUCS 41311
Gleichenella pectinata (Willd.) Ching T G NEO I, II, III HUCS 41498
Sticherus bifidus (Willd.) Ching T G NEO I, II HUCS 41386
Sticherus lanuginosus (Fée) Nakai T G NEO I, II, III HUCS 41312
Sticherus nigropaleaceus (J.W.Sturm) J.Prado & Lellinger T G NEO II HUCS 39492
Sticherus pruinosus (Mart.) Ching T G NEO I ICN 107002
HYMENOPHYLLACEAE
Abrodictyum rigidum (Sw.) Ebihara & Dubuisson T F NEO I ICN 176711
Didymoglossum hymenoides (Hedw.) Desv. T/E F NEO I, II, III HUCS 41365
Didymoglossum reptans (Sw.) C. Presl T/E F NEO I, II ICN 178344
Hymenophyllum caudiculatum Mart. T/E F NEO-ANT I ICN 178347
Hymenophyllum polyanthos (Sw.) Sw. E F PAN I ICN 42361
Hymenophyllum pulchellum Schltdl. & Cham. E F NEO I ICN 85305
Polyphlebium angustatum (Carmich.) Ebihara & Dubuisson E F NEO I, II, III ICN 161400
Polyphlebium pyxidiferum (L.) Ebihara & Dubuisson E F PAN I, II, III ICN 178355
Trichomanes cristatum Kaulf. T F NEO I, II ICN 176748
Trichomanes pilosum Raddi T G NEO I HUCS 41308
Trichomanes polypodioides Raddi E F NEO I ICN 178349
Vandenboschia radicans (Sw.) Copel. T/E F PAN I, II ICN 41391
Vandenboschia rupestris (Raddi) Ebihara & K.Iwats. T/E F NEO I ICN 178356
ISOETACEAE
Isoetes weberi Herter T W NEO-ATL II PACA 98839
LINDSAEACEAE
Lindsaea lancea (L.) Bedd. T F NEO I, II ICN 166179
Lindsaea quadrangularis Raddi T F NEO I, II HUCS 41383
LOMARIOPSIDACEAE
Lomariopsis marginata (Schrad.) Kuhn T/E F NEO-ATL I ICN 146209
Nephrolepis cordifolia (L.) C. Presl T G ANP I, III HUCS 41387
Nephrolepis exaltata (L.) Schott T G NEO III PACA 74470
Nephrolepis pectinata (Willd.) Schott T G NEO II ICN 129296
LYCOPODIACEAE
Diphasiastrum thyoides (Willd) Holub T G NEO I ICN 176735
Lycopodiella alopecuroides (L.) Cranfill T G NEO I, II, III, IV, V HUCS 41053
Lycopodiella tupiana (B. Øllg. & P.G. Windisch) B. Øllg. T G NEO-PAR II HAS 78174
Lycopodium clavatum L. T G COS I, III HUCS 41395
Palhinhaea cernua (L.) Franco & Vasc. T G/W PAN I, II, III HUCS 41396
Phlegmariurus acerosus (Sw.) B.Øllg. E F NEO I ICN 89978
Phlegmariurus fontinaloides (Spring) B.Øllg. E F NEO-ATL I HAS 40598
Phlegmariurus heterocarpon (Fée) B.Øllg. E F NEO-PAR I, II HAS 40596
Phlegmariurus mandiocanus (Raddi) B.Øllg. E F NEO-PAR I, II ICN 178336
Phlegmariurus quadrifariatus (Bory) B.Øllg. E F NEO-ATL I ICN 44523
Phlegmariurus reflexus (Lam.) B.Øllg. T F NEO II PACA 905
Pseudolycopodiella caroliniana (Silveira) Holub T G NEO I, II, III, V HUCS 41054
LYGODIACEAE
Lygodium volubile Sw. T F NEO I HUCS 41393
MARATTIACEAE
Eupodium kaulfussii (J.Sm.) J.Sm. T F NEO I ICN 124279
MARSILEACEAE
Marsilea ancylopoda A. Braun T W NEO I, III, IV HUCS 41269
Regnellidium diphyllum Lindm. T W NEO-PAM I, II, III, IV, V HUCS 41468
OPHIOGLOSSACEAE
Cheiroglossa palmata (L.) C.Presl E F PAN I, II ICN 178367
Ophioglossum crotalophoroides Walter T G NEO I, IV HURG 115
Ophioglossum nudicaule L. f. T G PAN I, II, III, IV ICN 47377
Ophioglossum reticulatum L. T G PAN I, II, III ICN 45109
OSMUNDACEAE
Osmunda regalis L. T G/F/W HOL I, II, III, IV, V HUCS 41052
Osmundastrum cinnamomeum (L.) C. Presl T G/F/W HOL III, IV HUCS 41466
POLYPODIACEAE
Campyloneurum acrocarpon Fée T F NEO-ATL I HUCS 41286
Campyloneurum austrobrasilianum (Alston) de la Sota E F NEO-PAR I, II, III HUCS 39495
Campyloneurum lapathifolium (Poir.) Ching T/E F NEO I ICN 152403
Campyloneurum nitidum (Kaulf.) C. Presl T F NEO I, II, III, IV HUCS 41482
Campyloneurum rigidum Sm. E F NEO-ATL I PACA 91198
Microgramma squamulosa (Kaulf.) de la Sota T/E G/F NEO I, II, III, IV, V HUCS 38881
Microgramma vacciniifolia (Langsd. & Fisch.) Copel. T/E G/F NEO I, II, III, IV, V HUCS 37778
Niphidium crassifolium (L.) Lellinger E F NEO I, II ICN 143984
Niphidium rufosquamatum Lellinger E F NEO I, II, III, IV HUCS 38943
Pecluma chnoophora (Kunze) Salino & Costa Assis T F NEO-PAR I HUCS 41545
Pecluma paradiseae (Langsd. & Fisch.) M.G. Price T F NEO-ATL I, II, III HUCS 41542
Pecluma pectinatiformis (Lindm.) M.G.Price E F NEO-PAR I, II, III ICN 168848
Pecluma recurvata (Kaulf.) M.G.Price E F NEO-PAR I ICN 184455
Pecluma robusta (Fée) M. Kessler & A.R. Sm. T F NEO-PAR I, III ICN 152424
Pecluma sicca (Lindm.) M.G.Price E F NEO-PAR I, II, III ICN 184456
Pecluma singeri (de la Sota) M.G.Price E F NEO-PAR I, II, III ICN 173093
Pecluma truncorum (Lindm.) M.G.Price E F NEO-PAR I ICN 184452
Phlebodium aureum (L.) J.Sm. E F NEO I, III ICN 184469
Pleopeltis astrolepis (Liebm.) E.Fourn. E F NEO I, II ICN 89945
Pleopeltis hirsutissima (Raddi) de la Sota E F NEO-PAR I, II, III, IV, V HUCS 39386
Pleopeltis lepidopteris (Langsd. & Fisch.) de la Sota T/E G/F NEO-PAR I, II, III, IV HUCS 41489
Pleopeltis macrocarpa (Bory ex Willd.) Kaulf. E F NEO I, II, III ICN 178372
Pleopeltis minima (Bory) J. Prado & R.Y. Hirai E F NEO I, II, III, IV HAS 48577
Pleopeltis pleopeltidis (Fée) de la Sota E F NEO-PAR I ICN 124179
Pleopeltis pleopeltifolia (Raddi) Alston E F NEO I, II, III, IV, V ICN 178389
Serpocaulon catharinae (Langsd. & Fisch.) A.R. Sm. T/E G/F NEO-PAR I, II, III, V ICN 161377
Serpocaulon fraxinifolium (Jacq.) A. R. Sm. T F NEO III ICN 176740
Serpocaulon latipes (Langsd. & L. Fisch.) A.R. Sm. T F NEO-PAR I, II, III HUCS 41318
Serpocaulon menisciifolium (Langsd. & Fisch.) A.R. Sm. T/E F NEO-ATL I, II HUCS 41317
PSILOTACEAE
Psilotum nudum (L.) P. Beauv. T/E G/F COS I, II, IV HUCS 41402
PTERIDACEAE
Acrostichum danaeifolium Langsd. & Fisch. T W NEO I, II, III, IV HUCS 41048
Adiantopsis cheilanthoides R.M.Senna T G NEO-ATL II PACA 87639
Adiantopsis chlorophylla (Sw.) Fée T G/F NEO I, II, III, IV, V HUCS 41476
Adiantopsis dichotoma (Cav.) T. Moore T G/F NEO-PAR II PACA 76701
Adiantopsis occulta Sehnem T F NEO-ATL I, III PACA 76714
Adiantopsis perfasciculata Sehnem T G/F NEO-ATL II, III HUCS 41509
Adiantopsis radiata (L.) Fée T F NEO II HAS 55620
Adiantum digitatum Hook. T F NEO II, III ICN 170488
Adiantum lorentzii Hieron. T F NEO-PAR I, II, III HUCS 41278
Adiantum pentadactylon Langsd. & Fisch. T F NEO-ATL I ICN 161367
Adiantum pseudotinctum Hieron. T F NEO-PAR I ICN 170491
Adiantum raddianum C.Presl T F NEO I, II, III, IV, V HUCS 41283
Anogramma leptophylla Link T F PAN III, IV HUCS 41381
Anogramma lorentzii (Hieron.) Diels T F NEO-PAR II, IV HUCS 41453
Doryopteris concolor (Langsd. & Fisch.) Kuhn T G/F PAN I, II, III, IV, V HUCS 41085
Doryopteris lomariacea Klotzsch T G NEO I, II HUCS 41370
Doryopteris lorentzii (Hieron.) Diels T G/F NEO I, II, III, IV HUCS 41358
Doryopteris nobilis (T. Moore) C. Chr. T F NEO IV HUCS 41464
Doryopteris pentagona Pic. Serm. T F NEO I, II, III, IV HUCS 41470
Doryopteris stierii Rosenst. T F NEO-ATL IV PACA 78525
Doryopteris triphylla (Lam.) Christ T G NEO I, II ICN 30816
Hemionitis tomentosa (Lam.) Raddi T F NEO II ICN 30814
Jamesonia osteniana (Dutra) J.G.Gastony T F NEO-PAR II HAS 44935
Pityrogramma calomelanos (L.) Link T G/F PAN I, II HUCS 38768
Pityrogramma chaerophylla (Desv.) Domin T G/F NEO I, II, III, IV HUCS 41291
Polytaenium lineatum (Sw.) Kaulf. E F NEO I ICN 89959
Pteris brasiliensis Raddi T F NEO I, II HUCS 41275
Pteris decurrens C. Presl T F NEO I HUCS 41277
Pteris defexa Link T F NEO I, III HUCS 41512
Pteris denticulata Sw. T F NEO I, II, III HUCS 41477
Pteris splendens Kaulf. T F NEO I, II ICN 14804
Tryonia myriophylla (Sw.) Schuettp., J.Prado & A.T.Cochran T F NEO-PAR I ICN 124325
Vittaria graminifolia Kaulf. T G NEO I HUCS 41534
Vittaria lineata (L.) Sm. E F NEO I, II, III, IV, V HUCS 42510
SALVINIACEAE
Azolla filiculoides Lam. A W NEO I, II, III, IV HUCS 39104
Salvinia auriculata Aubl. A W NEO I, II, III, IV HUCS 38703
Salvinia biloba Raddi A W NEO I, II, III, IV HUCS 41527
Salvinia minima Baker A W NEO II, III, IV HUCS 41271
SCHIZAEACEAE
Actinostachys subtrijuga (Mart.) C.Presl T F NEO III ICN 66739
Schizaea elegans (Vahl) Sw. T F NEO I ICN 66739
SELAGINELLACEAE
Selaginella marginata (Humb. & Bonpl. ex Willd.) Spring T F NEO I, II, III HUCS 41506
Selaginella microphylla (Kunth) Spring T F NEO I, II HUCS 67584
Selaginella muscosa Spring T F NEO I, II, III HUCS 41479
Selaginella tenuissima Fée T F NEO-ATL I PACA 89923
TECTARIACEAE
Tectaria incisa Cav. T F NEO I ICN 176738
Tectaria pilosa (Fée) R.C. Moran T F NEO I ICN 176714
THELYPTERIDACEAE
Macrothelypteris torresiana (Gaudich.) Ching T G/F/W PAN I, II, III HUCS 41076
Thelypteris abbiattiae C.F. Reed T F NEO-PAR I, III HUCS 41117
Thelypteris amambayensis Ponce T F NEO-PAR I, II, III, IV HUCS 41129
Thelypteris berroi (C.Chr.) C.F. Reed T F NEO-PAR III ICN 166493
Thelypteris conspersa (Schrad.) A.R. Sm. T F/W NEO I, II, III, IV HUCS 41116
Thelypteris decurtata (Link) de la Sota T F NEO I, IV, V HUCS 41115
Thelypteris dentata (Forssk.) E.P. St. John T G/F PAN I, II, III, IV, V HUCS 41113
Thelypteris hispidula (Decne.) C.F. Reed T F PAN I, II, III, IV HUCS 41111
Thelypteris interrupta (Willd.) K. Iwats. T G/F/W PAN I, II, III, IV, V HUCS 41083
Thelypteris metteniana Ching T F/W NEO-PAR I ICN 170570
Thelypteris oligocarpa (Humb. & Bonpl. ex Willd.) Ching T F NEO I ICN 126273
Thelypteris opposita (Vahl) Ching T G NEO I HUCS 38963
Thelypteris pachyrhachis (Mett.) Ching T F NEO I ICN 172983
Thelypteris patens (Sw.) Small T F NEO I, II, III ICN 14182
Thelypteris ptarmica (Mett.) C.F. Reed T F NEO-ATL I HUCS 41118
Thelypteris raddii (Rosenst.) Ponce T F NEO-ATL I, III ICN 107220
Thelypteris recumbens (Rosenst.) C.F. Reed T F NEO-PAR I, II ICN 14806
Thelypteris regnelliana (C. Chr.) Ponce T F NEO-PAR I HAS 43507
Thelypteris retusa (Sw.) C.F. Reed T F NEO-ATL I, II, III ICN 183474
Thelypteris riograndensis (Lindm.) C.F. Reed T F NEO-PAR I, III ICN 176183
Thelypteris rivularioides (Fée) Abbiatti T G/F/W NEO-PAR I, II, III, IV HUCS 41127
Thelypteris scabra (C. Presl) Lellinger T F NEO-PAR I, II HUCS 41389
Thelypteris serrata (Cav.) Alston T F NEO I, II ICN 161403

The gradual decrease in species richness along the Coastal Region was observed for all families, but particularly Polypodiaceae, Pteridaceae, Aspleniaceae and Thelypteridaceae, which represented more than 80% of the reduction. Some families such as Lygodiaceae, Marattiaceae and Tectariaceae were restricted to the extreme north. Others, such as Lindsaeaceae, Hymenophyllaceae, Lomariopsidaceae, Selaginellaceae, Dicksoniaceae and Schizaeaceae, occurred exclusively in the three northern-most latitudinal ranges (Fig. 3). Terrestrial taxa predominated with 162 species (75%), followed by epiphytes with 33 species (12%), while 24 species (10%) exhibited two different habits (epiphytic and terrestrial). Aquatic taxa were represented by four species (7% of total) (Fig. 4). With an increase in latitude, there was an increase in terrestrial species richness and a reduction in epiphytes. At the extreme north, the contingent of terrestrial species reached 70%, while at the extreme South it amounted to 78%, with a reduction of ca. 6% of epiphytic species in the north-to-south direction. Species that exhibited more than one habit were found mostly (80%) in forest environments.

Figure 3 Species richness by botanical family found in each latitudinal range. Note the reduction in the number of species from north-to-south in the CRRS. 

Figure 4 Preferred habit of fern and lycophyte species in different latitudinal ranges of the CRRS. I, II, III, IV and V: latitudinal bands of the CRRS. E: epiphytic ferns; T: terrestrial ferns; T/E: epiphytic and terrestrial ferns; A: aquatic ferns. 

A total of 159 (71%) species occurred exclusively in forest environments, while 26 were found in grassland formations. Some species were found both in forest and grassland habitats (15 spp., 15%). Nine species were present in wetland environments, and an equal number of species occurred in all three environments (forest, grassland and wetland). Blechnum brasiliense, Thelypteris conspersa and Thelypteris metteniana, occurred in forest and wetland habitats, whereas Blechnum schomburgkii and Palhinhaea cernua were found in grassland and wetland environments (Tab. 1). Differences in preference patterns for vegetation formations were identified over the studied profile (Fig. 5), with a decrease of forest species (-40%) and the increase in grassland/forest (+20%) and grassland/forest/wet land (+18%) species in the north-to-south direction.

Figure 5 Distribution of fern and lycophyte species in the different latitudinal ranges of the CRRS. I, II, III, IV and V: latitudinal ranges of the CRRS. CO: Cosmopolitan; AMP: Amphipacific; HOL: Holartic; PAN: Pantropical; NEO: Neotropical; NEO-PAM: Neotropical-Pampeana; NEO-ANT: Neotropical-Antartic; NEO-PAR: Neotropical-Paranaense; NEO-ATL: Neotropical-Atlantic. 

Taxa with wide global distributions were the most commonly observed with 140 species (63%), of which 113 were neotropical (51%), 17 pantropical, and two (Lycopodium clavatum and Psilotum nudum) cosmopolitan. The species Deparia petersenii and Nephrolepis cordifolia are amphipacific; Osmunda regalis and Osmundastrum cinnamomeum are Holarctic; and Blechnum cordatum, Lophosoria quadripinnata, Hymenophyllum caudiculatum and Equisetum giganteum are Neotropical-Antarctic. Species with restricted distributions represented 37% (83 species) with 44 being Neotropical-Paranaense, 38 Neotropical-Atlantic and one Neotropical-Pampean (Regnellidium diphyllum) (Tab. 1).

Floristic similarity analysis among the five latitudinal ranges revealed two floristically distinct regions in the CRRS: one formed by Ranges IV and V (South center and extreme South) and another formed by Ranges I, II and III (Middle center, North center and extreme North) (Fig. 6). Although they are grouped together, Ranges IV and V had low floristic similarity (53%), as did Ranges I, II and III (41%). Ranges I and II had 70% similarity, while ranges II and III were 73% similar. Only 21 species were common to all areas (Tab. 1).

Figure 6 Similarities among the five latitudinal ranges (Sørensen Similarity Indices) showing the floristic distinction between the group of Ranges I, II, III and the group of Ranges IV and V of the CRRS. 

Discussion

The species richness observed in this study corresponds to about 36% of the pteridophytic flora listed by Sehnem (1977) for the Southern Region of Brazil and 49% of that listed in Prado & Sylvestre (2015) for the state of Rio Grande do Sul. Most floristic studies on coastal ferns have been restricted to vegetation fragments, parks, conservation units or some specific synusiae (Behar & Viégas 1992; Labiak & Prado 1998; Kersten & Silva 2001; Santos et al. 2004; Dittrich et al. 2005; Athayde Filho & Windisch 2006; Gonzatti et al. 2014b). Despite having an extensive survey area, the richness observed in the present study is lower than that found by other authors in smaller tropical rain and Araucaria forest areas (Mynssen & Windisch 2004; Schwartsburd & Labiak 2007; Salino & Almeida 2008; Prado & Labiak 2009; Gasper & Sevegnani 2010; Souza et al. 2012), all of which were in lower latitudes.

In spite of the existence of a mountain chain (Serra do Mar), which harbors high fern and lycophyte species richness and serves as a corridor connecting the Southeastern and Southern Regions of Brazil (Tryon & Tryon 1982; Windisch 1996), a pronounced floristic reduction is evident between the two regions (Fig. 7). As an example, several fern and lycophyte genera, such as Doryopteris (Tryon 1942), Phlegmariurus (Windisch 1996) and Asplenium (Sylvestre & Windisch 2003), have high species richness and endemism in the Atlantic Forest of southeastern Brazil, but are strongly affected by latitudinal changes and experience a reduction in floristic richness towards the southern sector of the Atlantic Forest. However, the floristic richness found in CRRS is 82% higher than the fern and lycophyte flora of Uruguay further to the south (Legrand & Lombardo 1958; Zuloaga et al. 2008), indicating the continuation of floristic reduction through Uruguay to southern Argentina (Ponce et al. 2002).

Figure 7 Pattern of decreasing species richness for some genera of ferns and lycophytes present in southeastern and southern Brazil, as well as along the CRRS and Uruguay. SE BR (southeastern Brazil), SO BR (southern Brazil), RS I, II, III, IV and V (latitudinal ranges of the CRRS) and Ury (Uruguay). Data according to Prado & Sylvestre (2015) and Zuloaga et al. (2008). 

In the Neotropics, plant species richness is more strongly correlated with precipitation than edaphic variation (Gentry 1988). In the Atlantic Forest, patterns of floristic change of arboreal vegetation along latitudinal gradients have been attributed to variation in temperature and rainfall distribution. These climatic variables are important in differentiating richness and floristic composition of families, genera and species (Oliveira-Filho & Fontes 2000). The same authors verified that rainfall and temperature increments influence processes of tropicalization and changes in vegetation types, mostly when associated with increased latitude. For Atlantic Forest ferns and lycophytes, variables such as precipitation and evapotranspiration determine plant species composition in distinct vegetation types, as also discussed by Gasper et al. (2013).

Large-scale changes in diversity related to latitudinal gradients have been previously reported for ferns and lycophytes by Moran (2008), with several examples of the concentration of species richness in tropical regions with accentuated decreases towards both poles. According to this author, in South America, particularly in the tropical region, fern and lycophyte richness can reach 2,000 species, while in temperate regions it is only 79 species. Sato (1982) points out that in Japan, species richness decreases with increasing latitude, mostly due to climatic conditions.

Through the southern portion of CRRS, there was a reduction of the floristic richness of most families and genera. In addition to the reduction of fern and lycophyte total diversity, the incidence of species with Neotropical-Atlantic and Neotropical-Paranaense geographical distribution patterns was strongly affected. Taxa that maintain their distributions along the profile (21 spp.) have a wide Neotropical or global distribution (Tab. 1), and their occurrence extends to Uruguay (Legrand & Lombardo 1958; Zuloaga et al. 2008).

The extended distribution of many tropical species in the CRRS can be interrupted by alterations to the north-to-south forest continuity. The transition from tropical rain forest to other vegetation types such as grasslands, peat forests, sandy forests, seasonal forests and riparian habitats (Waechter 1990) can affect distribution patterns and inhibit dispersal of ferns and lycophytes. In Rio Grande do Sul, tropical rain forest reaches its southern limit at the 30º S parallel in the region of Osório - RS (Rambo 1951; 1954; Lorscheitter 2003). These formations develop on the extreme southern slopes of the "Serra do Mar" and on the eastern face of "Serra Geral". Due to the climatic conditions of temperature and precipitation, as well as the environmental heterogeneity of vegetation and substrates, the development of larger forests with tropical species are allowed, as is the dispersal of northern floristic components (Rambo 1951; Klein 1984; Waechter 1985; Waechter 1990). These characteristics of environment heterogeneity are fundamental to increasing fern and lycophyte diversity in the Atlantic Forest (Windisch 1992; Dittrich et al. 2005), and they were not observed in CRRS Ranges III, IV and V.

Phytogeographically, the latitude 30º S defines the limit between the Atlantic and Paranaense provinces where pluvial and subtropical forests (Atlantic Forest) find their southern limit, and are gradually replaced by herbaceous elements of the Pampa biome (Cabrera & Willink 1980). Sota (1973) considers that the Pampa, along with the Chaco, are barriers separating the center of fern and lycophyte diversity in southern Brazil from the Argentinian and Chilean centers of diversity. According to Prado & Hirai (2014), the Pampa biome is the poorest in fern and lycophyte diversity, with only 0.5% of the floristic richness found in the Atlantic Forest.

This same reduction in diversity has been reported previously by other authors. Rambo (1950; 1951; 1954; 1956) observed structural and floristic modifications to vegetation along the Coastal Region, attributing the decrease in species richness to the dispersal processes that occurred throughout the region he referred to as "Porta de Torres" ("Torres migrational gate"). This latitudinal gradient was later observed by Waechter (unpublished data) in a study of vascular epiphytes, who found a 93.7% reduction in richness between latitudinal Range I and Range V. In his work with epiphytic orchids, Waechter (1998) found that there is a total reduction in species richness along the CRRS, a 88% reduction between Range I and Range II, and that no species reached south of parallel 33° S. Of the 61 genera he studied, only four are found in Uruguay and one in the province of Buenos Aires (Argentina).

Among the factors that influence floristic change in the north-to-south direction of the CRRS, Waechter (1990) highlights climatic discontinuity along the region. The author noted that the decrease in rainfall and temperature going south causes an increase in the number of cold days and annual frost events. This, in turn, results in changes to vegetation communities, causing insularization and discontinuity of the arboreal component, thus interfering in the dispersal routes of tropical plant species.

Although a strong floristic discontinuity has been reported for the region of parallel 30° S (Waechter 1990; 1998), our data indicate that for ferns and lycophytes this discontinuity occurs mostly from parallel 31° southwards (Fig. 7), where a reduction in species richness and the differentiation of the floristic elements in Ranges I, II, and II vs. Ranges IV and V were observed. These results can be associated with the high dispersal capacity of fern and lycophyte spores, thereby finding niches with favorable conditions for their establishment and reproduction (Tryon 1970; Wolf et al. 2001), or simply forest connections (present and past) that allowed for a broader distribution.

Our results indicate that more species occur in more than one environment (forest/grassland or forest/grassland/wet land) with increasing latitude, and that there is a decrease of strict forestalls. The strong dependence of ferns on forest environments can be related to the group's evolutionary history, which suggests that 80% of current ferns evolved in forest environments after the angiosperm radiation ca. 100-65 mya (Schneider et al. 2004).

Another north-to-south floristic change in the CRRS can be seen in the reduction of epiphytic species in Range V with the concomitant prevalence of terrestrial species (Fig. 5). Beyond the need for adequate ecological conditions (Sota 1971; Benzing 1987), there is the requirement of host plant availability for the establishment of epipytic species (Waechter unpublished data).

Some species restricted to Range I, such as Vandenboschia radicans, Lomariopsis marginata, Mickelia scandens, Polybotrya cylindrica, Olfersia cervina, are hemiepiphytes, that begin development on the ground and later climb host plants. These species are extremely dependent on environments with high levels of humidity such as is found in the interior of forests without edge effects and external light incidence (Orihuela & Waechter 2010; Orihuela et al. 2013).

Decreased amounts of rainfall and the existence of a drier season in the extreme south can limit the establishment and development of fern and lycophyte flora. Ranal (1995a) points out that fern spore germination, as well as the development of the gametophyte and sporophyte, are strongly affected by desiccation. In experiments focusing on survival, Ranal (1995b) shows that 30% of fern gametophyte deaths are due to desiccation. Watkins et al. (2007) demonstrated that the gametophytes of xerophytic species, as well as epiphytic and some terrestrial species, are better adapted to survive conditions of scarce water, contrary to mesophytic species, which cannot undergo periodic variations in their water content.

Other features inherent to the reproductive success of many ferns and lycophytes can be decisive in their establishment in particular habitats. Although this group of plants is capable of dispersing spores over long distances (Holttum 1938) and can form spore banks in the ground (Ranal 2003), the spores may not encounter the microclimatic (temperature, humidity and luminosity) and biotic conditions (mycorrhizal associations) needed for germination (Williams 1938; Sheffields 1996). Furthermore, gametophytes, even when possessing adaptations to desiccation and variable conditions of pH, soil nutrition, temperature and luminosity (Farrar et al. 2008), can suffer from insufficient availability of free water in the environment, which in and of itself can be a limiting factor to their establishment. Despite the fact that some fern species have strategic adaptations for independent gametophytic reproduction (apogamy, clonal reproduction by gemmae, pH metamorphosis) the presence of water is still a requirement for the successful sexual reproduction of the gametophyte of most fern and lycophyte species (Page 2002). According to Holttum (1938), the majority of fern and lycophyte spores germinate in forest environments, and to occupy other environments with adverse conditions they need specific adaptations.

The occurrence of ferns in wetland and grassland environments is also related to expansion of these vegetation formations in the north-to-south direction, with the expansion of water bodies in wetland-region lagoons and natural grasslands most frequent in Range V. For example, Blechnum brasiliense has adapted to a variety of environments that differ in their edaphic composition, vegetation formations and microclimate conditions (Silva et al. 2013).

Data compiled by Nimer (1990) and Moreno (1961), point out clear differences in the climatic patterns of the two extremes of CRRS. According to these authors, the average annual precipitation can be up to 300 mm/year lower and the average temperature about 2ºC lower in Range V. Furthermore, the average number of days with frost increases from three to 15 days in the extreme south (Range V). This southern, more temperate climate can explain the presence of species with Neotropical-Antarctic or Holarctic distribution patterns in the floristic composition of Range V, such as Osmunda regalis and Equisetum giganteum.

Studies published by Bremer & Jongejans (2010) on the population dynamics of Asplenium scolopendrium show the negative effect of frost on the survival and, consequently, the retrogression of this species. According to these authors, frost affects fern sporophytes in three ways: direct mortality by freezing caused by wind, soil freezing, and hydric unavailability caused by ice. In populations submitted to 22 continuous days with frost, mortality reached 38%. In order for this species to occur in these regions of low temperatures and frost, adaptations at all development stages are required. In several cases phenological changes take place that permit survival and ensure the reproductive success during cold periods (Sato & Sakai 1980; Sato & Sakai 1981; Sato 1982).

Although the best temperatures for spore germination and gametophyte growth are generally considered to be between 20° and 30°C (Miller 1968), various exceptions have been observed. In northeastern United States, gametophytes of the genus Vittaria Sm. can become established in certain environments, form extensive populations through asexual reproduction by apogamy and persist during prolonged frost while the sporophytes do not survive, dying at the beginning of their development (Farrar 1978). These reports were also corroborated by Sato & Sakai (1980) for many Asiatic species, where the gametophytic phase can resist temperatures below -40°C, while their sporophytes do not survive in temperatures below 0°C. This limiting factor can be associated with the decrease of species richness (at least in the sporophyte phase) in the extreme south of CRRS, where the species are more adapted to such conditions, such as Osmundastrum cinnamomeum whose sporophyte can resist -10°C (Sato 1982).

Sehnem (1977) suggested that the low richness of ferns and lycophytes in some regions of the state of Rio Grande do Sul is influenced by the reduced amount of time for the migration of additional species (recent paleogeographic evolution) and, consequently, the limited distribution of these species in the extreme south. This phenomenon may explain the decrease of fern and lycophyte species in the temperate floras of the "Southern Cone", which can have three to four times fewer species than tropical floras such as in southeastern Brazil (Ponce et al. 2002).

The impoverishment of the extreme southern flora of CRRS may also be related to past paleoenvironmental conditions. Paleogeographic and palynological evidence point to the existence of an arid climate and the prevalence of grassland vegetation across southern Brazil that persisted at least until the beginning of the Holocene, when the migration of the tropical vegetation of southeastern Brazil to CRRS started (Ab'Sáber 1977; Ledru et al. 1998; Lorscheitter 2003).

Rising humidity patterns in the past 4,000 years show the expansion of fern and lycophyte communities in "Laguna dos Patos" (Middle center of the Coastal Region) (Lorcheitter 2003 ), which could not have occurred in the extreme South, due to climatic conditions. Recent palynological data from the Holocene period (Masetto & Lorcheitter 2014) establish the presence of taxa currently not found in the region, indicating alterations in the current floristic composition, or in the process of long distance dispersal.

The most striking outcome of our study was the high floristic richness present in the Coastal Region of the state of Rio Grande do Sul and the high reduction in species richness of ferns and lycophytes along the north-south extremes of RCRS. There are a variety of factors, including climatic limitations, dynamic phytogeography and the biology of ferns and lycopods themselves that have been considered in explaining these observations.

Acknowledgments

The authors thank the curators of the cited herbaria for their welcoming assistance and our colleague Flávia Diniz da Silva for assistance in the field work. The CAPES and CNPq for providing a scholarship to the first author and research grant to the third author.We thank the "Universidade Federal do Rio Grande do Sul" (UFRGS) and the "Universidade de Caxias do Sul" (UCS) for permitting the use of their facilities. We are grateful to all the reviewers of this manuscript.

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Received: February 22, 2016; Accepted: March 21, 2016

* Corresponding author: fgonzatti@ucs.br

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