Plant endemism in the Sierras of Córdoba and San Luis (Argentina): understanding links between phylogeny and regional biogeographical patterns

Abstract We compiled a checklist with all known endemic plants occurring in the Sierras of Córdoba and San Luis, an isolated mountainous range located in central Argentina. In order to obtain a better understanding of the evolutionary history, relationships and age of the regional flora, we gathered basic information on the biogeographical and floristic affinities of the endemics, and documented the inclusion of each taxon in molecular phylogenies. We listed 89 taxa (including 69 species and 20 infraspecific taxa) belonging to 53 genera and 29 families. The endemics are not distributed evenly, being more abundant in the lower than in the middle and upper vegetation belts. Thirty-two genera (60.3%) have been included in phylogenetic analyses, but only ten (18.8%) included local endemic taxa. A total of 28 endemic taxa of the Sierras CSL have a clear relationship with a widespread species of the same genus, or with one found close to the area. Available phylogenies for some taxa show divergence times between 7.0 – 1.8 Ma; all endemic taxa are most probably neoendemics sensu Stebbins and Major. Our analysis was specifically aimed at a particular geographic area, but the approach of analyzing phylogenetic patterns together with floristic or biogeographical relationships of the endemic taxa of an area, delimited by clear geomorphological features, could reveal evolutionary trends shaping the area.


Introduction
Why are endemic taxa important?
'Th e study and precise interpretation of the endemism of a territory constitute the supreme criterion, indispensable for arriving at any conclusions regarding the origin and age of its plant population. It enables us better to understand the past and the transformations that have taken place. It also provides us with a means of evaluating the extent of these transformations, the approximate epoch when they occurred, and the eff ects which they produced on the development of the fl ora and the vegetation' (Braun-Blanquet 1923: 223). Although many studies have dealt with the origin, classifi cation and biology of endemism (e.g. Stebbins and Major 1965, Kruckeberg and Rabinowitz 1985, Hobhom 2013, this simple sentence by Josias Braun-Blanquet (1884-1980 illustrates well how some basic good defi nitions last through time. Th e study of plant endemism is important because it could improve our knowledge of the fl ora of a region in at least two diff erent respects, which are briefl y discussed below.

Biogeography and evolution
Th e fi rst aspect, perhaps the most traditional, has to do with biogeography and evolution of plants. Th e work of Stebbins and Major (1965) on the endemics of California outlined the basic elements to analyze when dealing with the endemic fl ora of a region: a) the fl oristic affi nities and distribution of the endemics; b) the relationships of the endemic species with congeners (particularly for widely distributed taxa); c) the availability of a fossil record; and d) the use of genetic data to diff erentiate paleo-from neo-endemism.
Th ese two concepts, paleo and neoendemic (Stebbins and Major 1965) apply to: a) ancient vestiges of taxa that were once more widespread, with their present distribution being a relict resulting of the reduction of their original habitats over time (paleoendemics); and b) relatively young species have only recently diverged from a parental entity, usually a widespread species (neoendemics).
Th e concepts of fl oristic affi nities and fossil record availability have still more or less the same meaning as in the 1960's, but today genetic data often provides a phylogenetic or phylogeographic context; these disciplines have matured into essential tools to understand evolutionary processes.
Biogeography counts the study of endemics and its distribution as one of its main subjects, since the existence of endemic taxa is related to geographic areas (Crisp et al. 2001). Both endemic taxa and restricted geographic areas are part of the same concept -i.e. taxa are considered endemic when they occur in a restricted area (Anderson 1994). Many studies have focused on the detection of areas of endemism (e.g. Myers et al. 2000, Crisp et al. 2001, Murray-Smith et al. 2009); a substantial number of endemic species in a geographical region often correlates with age and isolation of the area as these factors infl uence both the evolution (the formation and development of new taxa) and survival (the permanence of endemic relicts) (Lesica et al. 2006).

Conservation
How should policy makers set priorities for conservation? Narrow endemic taxa often have priority in setting conservation policies (Chaplin et al. 2000) because narrow endemic plants are by defi nition rare, and in consequence face higher extinction risk due to environmental change (Crisp et al. 2001). Although there is controversy about what should be conserved, areas with high numbers of endemic species (hot spots) are often a preferred object of conservation policies and strategies because they off er the best reward for investment in conservation (Myers et al. 2000, Lamoreux et al. 2006, Ferreira and Boldrini 2011. But while Myers et al. (2000) defi ned 25 major biodiversity hotspots, and some have been well studied, e.g. the Brazilian Atlantic forest (Tabarelli et al. 1999, Morellato andHaddad 2000), there is still very little information on areas other than these 25 'major' biodiversity hotspots, even though these are areas with fewer, but still a substantial number of, endemic species.
Among all biotas, mountainous regions are especially rich in plant endemic species with restricted distribution, since those areas represent discontinuities in soil conditions and topography that promote diff erentiation in plant populations (Kruckeberg and Rabinowitz 1985;Lesica et al. 2006). Th e Sierras of Córdoba and San Luis ("Sierras CSL") represents such an area, extending ca. 550 km in NE-SW length and about 110 km width, with the highest point represented by the Cerro Champaqui (2790 m). Sierras CSL are located in the center of Argentina, between 29° and 33°S, mostly in Córdoba and San Luis Provinces, except for a small northern portion extending into the neighboring province of Santiago del Estero (Fig. 1). With an overall northeastsouthwest orientation and composition of Precambrian metamorphic blocks, the Sierras CSL are older than the Andes; they rise above Pampa plains of Quaternary origin (Baldo et al. 1996), and comprise six main sections (from north to south): Sierras del Norte, Sierras Chicas-Las Peñas, Sierras Grandes-Sierra de Comechingones, Sierras de Pocho-Guasapampa, Sierra de San Luis and Sierra del Morro ( Fig. 1) (Carignano 1999). Biogeographically, the fl ora of the Sierras CSL belongs to the Chaco Province of the Chacoan subregion (Morrone 2006); this is mainly xerophytic forest with shrubs and trees up to 15 m high (Cabrera and Willink 1980;Prado 1993a, b;Giorgis et al. 2011). Luti et al. (1979 described three main altitudinal vegetation belts for the Sierras CSL: the sierra forest, between 500 and 1300 meters above sea level; the sierra shrubland, between 1300 and 1700 meters; and fi nally, the altitude grasslands and woodlands, from 1700 meters upwards (Fig. 2). Th e upper belt is fl oristically diff erent from the other two and shows affi nities with Andean and Patagonian fl oristic elements (Cabido et al. 1998;Prado 1993a) and contains several endemics restricted to this altitude (Cabido et al. 1998). Of the three vegetation belts, the lower is the most exposed to anthropogenic threats because it lies close to the second largest city of Argentina (Córdoba); the attractive landscapes of the Sierras are also a preferred holiday destination in the country. Additional anthropogenic disturbances include fi res and livestock grazing (Cingolani et al. 2013).
Th e implementation of conservation strategies needs in the fi rst case basic information on the taxa object of potential conservation. Since previous works hinted at many endemic taxa present in the Sierras CSL (Cabido et al. 1998, Cantero et al. 2011, Oggero and Arana 2012, but specifi c evaluation of the endemic taxon richness of the Sierras CSL has not been done, we compiled a critical list of all species and infraspecifi c taxa endemic to the region. We then assessed the inclusion of the listed endemic taxa in molecular phylogenetic studies, as a means to estimate the evolutionary history of each studied taxon, specifi cally verifying relationships and divergence times (when available).

Methods
We compiled a list using online resources, in particular Zuloaga et al. (2008) (updated to December 2014; http://www2.darwin.edu.ar/Proyectos/FloraArgentina/FA.asp) and the database of endemic plants of Argentina (http://www.lista-planear.org). We verifi ed both the endemic status and the distribution of each taxon restricted to the Sierras CSL as defi ned by a cut-off altitude limit of 200 m. (i.e. endemic taxa from Córdoba and/or San Luis provinces found below this elevational limit were excluded from the list). Verifi cation of taxa also included checking the validity of names and common synonyms; since estimates of biodiversity relies upon counting species names, including synonyms or nomina dubia would aff ect estimates of endemism (Alroy 2002). After this validation, we searched for information for each taxon regarding: 1) distribution, including altitudinal range; 2) life-form; 3) number of species in the genus; 5) inclusion in a molecular phylogenetic study; and 6) relationship to a widespread taxon of the same genus.

Results
Of the relevant elements for studying endemism recognized by Stebbins and Major (1965), only the fl oristics of the Sierras CSL has been well studied (Cabido et al. 1987(Cabido et al. , 1998Giorgis et al. 2011 and references therein), while the currently known fossil record is too sparse to be useful for studies of current vegetation (Leguizamon 1972, Balarino andGutierrez 2006). We list 89 taxa (69 species and 20 infraspecifi c taxa, belonging to 53 genera and 29 families), which are found only in the provinces of Córdoba and San Luis at elevations above 200 m. Distribution, elevation and life form of each taxon are summarized in Table 1. Th e genus with the most endemics is Gymnocalycium, with 16 taxa. Aristida, Gomphrena, Hieracium, Nassella, Portulaca, Siphocampylus, Senecio

Distribution of the endemic taxa
Th e altitudinal distribution of the endemic taxa in the Sierras CSL is shown in Table  2 and Fig. 2. Th ere are exclusive taxa (i.e., present only in a single altitudinal belt) and also shared taxa (present in more than one altitudinal belt). Among the exclusive taxa, the lower Sierra forest belt has 35 taxa, the intermediate Sierra shrubland belt has 2 taxa and the upper grasslands and woodlands belt has 11 taxa. Th e presence of taxa in more than one belt is depicted in the last three columns of Table 2, that shows which taxa are present in which combination of belts; among the taxa which are present in two belts, the combination of lower and middle belts has 17 taxa and the combination of middle and upper belts has 7 taxa. Finally there are 17 taxa that are present in all the three belts.

Phylogenetic knowledge of the endemic taxa of the CSL Sierras
Th e inclusion of the endemic taxa of the Sierras CSL in phylogenetic studies has been minimal; from a total of 53 genera with endemic taxa present in the area, 32 (60.3%) have been included in at least one molecular phylogenetic analysis, but only 10 studies (18.8%) have a species endemic to the Sierras CSL: Acanthocalycium, Blumenbachia, Eryngium, Escallonia, Grindelia, Gymnocalycium, Portulaca, Prosopis, Sphaeralcea and Tillandsia (Table 3).
Assessment of the phylogenetic knowledge of the genera with endemic taxa of the Sierras CSL.

Carex. Th is cosmopolitan genus comprises 1500-2000 species in both Northern and
Southern hemispheres (Wheeler 1990); 107 species are found in Argentina (Zuloaga et al. 2008). Th e Sierras CSL endemic C. monodynama is found in an isolated location at the summit of the Sierra de Achala, but has not been included in molecular phylogenies. Cenchrus. Grass genus with ca. 100 species of tropical and temperate regions of both hemispheres; 14 species are found in Argentina (Gutiérrez 2012). Th e Sierras CSL endemic C. rigidus has not been included in a molecular phylogeny. Cerastium. Th e nearly cosmopolitan genus Cerastium comprises ca. 100 species with a diversity center in Eurasia and has preference for cold-temperate regions (Pedersen 1984); two migration events to North and South America have been suggested (Scheen et al. 2004). In Argentina there are 17 spp., from which the Sierras CSL endemic C. argentinum has never been included in a molecular phylogenetic study. Danthonia. 30 species mainly from mountainous regions of the Southern Hemisphere; 7 species in Argentina . Th e Sierras CSL endemic D. melanathera has not been included in any molecular phylogeny.
Eryngium. Th e largest genus in the Apiaceae, with about 250 species of temperate regions of all continents; 29 species are found in Argentina (Zuloaga and Morrone 1999). Th e Sierras CSL endemic E. agavifolium was included in the molecular phylogeny by Calviño et al. (2008), forming a clade with E. elegans, a widely distributed species in southern South America. Escallonia. Th e South American genus Escallonia comprises ca. 40 species of shrubs, especially in the Andes. In Argentina there are 16 species (Zuloaga et al. 2008) and the Sierras CSL endemic E. cordobensis has been included in the phylogenetic study of Sede et al. (2013), forming a polytomy with E. petrophila, E. ledifolia, E. farinacea, E. bifi da and E. laevis, which are taxa distributed in northeastern Argentina, Brazil, Paraguay and Uruguay. Gentianella. Th is mostly alpine-arctic genus occurs in South America in the Andes, where is represented by ca. 150 species (von Hagen and Kadereit 2001), with about 28 species in Argentina (Zuloaga and Morrone 1999). Gentianella entered in South America probably more than one time, and has in the region a high rate of speciation, probably linked with the availability of suitable habitats (von Hagen and Kadereit 2001). Th e Sierras CSL endemic annual G. parvifl ora has not been included in a molecular phylogeny. Geranium. Genus with ca. 400 species of temperate areas and tropical mountains throughout most of the world, and 18 species in Argentina (Zuloaga and Morrone 1999). Th ere is no molecular phylogenetic study of the whole genus. Aedo et al. (2005) revised section Andina of the genus, to which the endemic of CSL Sierras G. parodii belongs. Aedo et al. (2005) note that G. parodii was fi rst described as a variety of the wider distributed G. sessilifl orum, which is found in the Andes from Perú to southern Argentina and Chile. Geum. Th is mostly Northern Hemisphere (Smedmark and Eriksson 2002) genus comprises ca. 40 species of cold-temperate regions. In Argentina it includes 6 species, commonly found in the Andes and Patagonia. Th e Sierras CSL endemic Geum brevicarpellatum has not been included in a phylogeny. Gomphrena. Th is genus includes ca. 120 spp. of tropical regions, with 38 species in Argentina (Borsch 2008b). G. pulchella subsp. rosea and G. pulchella var. bonariensis are restricted to the Sierras CSL, but G. pulchella is widely distributed in southern South America. Th ere is no molecular phylogenies including these taxa. Grindelia. A New World temperate genus with 73 species in western North America and southern South America (Sancho and Ariza Espinar 2003); 19 species in Argentina (Freire 2008). Th ere are two endemic taxa in the Sierras CSL, G. cabrerae var. alatocarpa and G. globularifolia. Th e latter was included in the phylogeny by Moore et al. (2012), and resolved within the South American clade. Gymnocalycium. South American genus of ca. 50 species, mostly in mountain ranges of Argentina; with 16 endemic species and subspecies in the Sierras CSL, is the genus with largest number of endemic species in the region (Demaio 2012). Th e phylogeny of the genus by Demaio et al. (2011) recovered three clades (subgenera) living sympatrically in the Sierras CSL: Scabrosemineum (6 endemic taxa); Gymnocalycium (9 endemic taxa); and Trichomosemineum (1 taxon). Divergence times in Cactaceae (Arakaki et al. 2011) showed that the diff erentiation of the genus might have occurred between the Miocene and Pliocene (7.5-6.5 Ma); Hernández-Hernández et al. (2014) gave a younger date of 5.08 (3.09-7.55) Ma. Habranthus. American genus of ca. 30 species, mostly South American but with fi ve species in North America, probably introduced (Roitman et al. 2007). Twenty three species grow in Argentina (Zuloaga et al. 2008). Th e Sierras CSL endemic H. sanavironae is similar in fl owers size to Habranthus robustus (=Zephyranthes robusta) (Roitman et al. 2007), which is widespread in Central Argentina and Southern Brazil. H. sanavironae has never been included in a phylogeny. Helenium. American genus of ca. 40 species, mostly southern USA and Mexico (Bremer 1994); in Argentina three species (Novara and Petenatti 2000). Th e Sierras CSL endemic H. argentinum has never been included in a molecular phylogeny. Hieracium. Nearly cosmopolitan genus with ca. 1000 species (Bremer 1994); 45 species in Argentina (Cerana and Ariza Espinar 2003). Presence of polyploidy, mixed breeding systems and apomixis (Chrtek et al. 2009) complicate its systematics and make estimation of taxon numbers highly variable. None of the Sierras CSL endemics (H. achalense, H. cordobense and H. criniceps) have been included in molecular phylogenetic studies. Hypochaeris. Th is genus with ca. 60 species occurs in Europe, Asia and North Africa, and South America, while the greatest number of species is found in the latter (Bremer 1994); 30 species are found in Argentina (Bortiri 1999). Studies by Samuel et al. (2003) and Tremetsberger et al. (2005) did not include the Sierras CSL endemic H. caespitosa. Hysterionica. South American genus with 12 species in Brazil, Uruguay and Argentina; 9 species are found in Argentina (Freire 2008). Th e Sierras CSL endemics H. dianthifolia var. dianthifolia and H. dianthifolia var. pulvinata have not been included in molecular phylogenies; Noyes and Rieseberg (1999) related this genus with Conyza and Erigeron, both of the Northern hemisphere. Isostigma. Small South American genus with 11 species from subtropical areas; 5 species are found in Argentina (Peter 2009 (Zuloaga and Morrone 2012). Th e genus is rich in narrow endemics (Simon et al. 2011). Mimosa cordobensis has not been included in a phylogenetic study. Mostacillastrum. Th is South American genus comprises 17 species distributed from southern Peru and Bolivia to northern Patagonia (Al-Shehbaz 2006); Mostacillastrum carolinense was described originally as a Sisymbrium (Scappini et al. 2004). Th e phylogeny by Warwick et al. (2009) included other Mostacillastrum species but not M. carolinense; the tribe Th elypodieae where Mostacillastrum belongs shows low molecular diff erentiation. Mutisia. Excepting for a few species growing in southern Brazil and adjacent regions of Paraguay and Uruguay, most of the 59 species of this genus are found in the Andes (Cabrera 1971). Argentina has 35 species (Freire 2008) and the Sierras CSL endemic M. castellanosii var. comechingoniana has never been included in a phylogenetic study. Nassella. Grass genus with ca. 80 species distributed in the American continent, especially in the Andes (Mabberley 1997). Due to diff erent generic concepts, the species number in Argentina varies between 16 (Rosa et al. 2005) and 70 (Cialdella 2012). Th e Sierras CSL endemic N. stuckertii, related to the widespread N. tenuissima, has not been included in molecular phylogenies. Nothoscordum. Th is mostly South American genus comprises more than 70 species, with 39 in Argentina and a single species, N. gracile, distributed through the Americas (Zuloaga et al. 2008;Rodrigues Souza et al. 2012). Th e Sierras CSL endemic N. achalense has not been included in a phylogenetic study. Parodianthus. Small genus with only two known species, restricted to central Argentina. Pardianthus capillaris grows only in the northern extreme of the Sierras CSL. Marx et al. (2010) showed Parodianthus formed a clade with Casselia and Tamonea in agreement with previous morphological studies ( Martínez and de Romero 2003), but did not include the Sierras CSL endemic P. capillaris. Casselia is distributed in Brazil, Bolivia, and Paraguay, while Tamonea is widespread from Mexico and the Caribbean to Brazil and Paraguay. Plantago. Th e ca. 260 species of Plantago are distributed worldwide (Dunbar-Co et al. 2008); in Argentina there are 34 species (Zuloaga et al. 2008). Th e Sierras CSL endemic P. densa has never been included in a molecular phylogeny. Poa. Th e largest genus of the Poaceae, with a number varying between 500-575 species distributed in all temperate-cold regions of the world (Gillespie and Soreng 2005;Gillespie et al. 2007). Th ere are 62 species in Argentina (Giussani et al. 2012), and from the two Sierras CSL endemics, P. hubbardiana and P. stuckertii, only the latter has been included in a phylogeny (Gillespie et al. 2007), where it was placed together with the North American P. arachnifera. Portulaca. Distributed worldwide, this genus comprises ca. 100 species, mainly in the tropics and subtropics, with centers of diversity in South America and Africa. Th ere are 29 taxa in Argentina, including the Sierras CSL endemic P. confertifolia var. cordobensis (Zuloaga et al. 2008). A recent molecular phylogeny included P. confertifolia (Ocampo and Columbus 2011) and showed the node including this species is dated to 3 Ma.

Prosopis.
Th is genus comprises 45 species of warmer regions of America, Southeast Asia and Africa. Th ere are 28 spp. in Argentina (Zuloaga and Morrone 1999), and the Sierras CSL endemic P. campestris has been included in the phylogenetic study by Catalano et al. (2008). Th e study shows a probable divergence time during the late Pliocene (1.8 Ma). Senecio. One of the most species-rich genera of the Asteraceae, Senecio has ca. 3000 species distributed all over the world. In Argentina there are 423 species (Freire 2008), with regions of highest diversity the Andes and Patagonia (Cabrera 1971). Th e two Sierras CSL endemics, S. achalensis and S. retanensis have never been included in any phylogenetic study. Siphocampylus. South American genus with ca. 220 species, 16 growing in mountainous regions of Argentina. Neither endemic variety of S. foliosus endemic to the Sierras CSL has been included in any phylogenetic study. Solanum. Sub-cosmopolitan genus with around 1400 species of warm regions of the world. In Argentina there are 115 species and three hybrids (Barboza 2013). Th e three Sierras CSL endemics, S. concarense, S. ratum and S. restrictum have not been included in phylogenetic studies; S. concarense has been accepted by Barboza (2013), but S. restrictum and S. ratum were treated as synonyms of S. salicifolium, an extremely variable species distributed in western Argentina and Bolivia. Soliva. Small and mostly South American genus, it also has widespread species that occur in both Australia and North America. 5 species grow in Argentina (Zuloaga et al. 2008). Th e molecular phylogeny of the tribe Anthemideae by Watson et al. (2000) did not include the Sierras CSL endemic S. triniifolia but S. anthemifolia, a widespread species occurring in adjacent areas. Sophora. Cosmopolitan genus with ca. 45 species; 2 species in Argentina. Sophora linearifolia is endemic to the Sierras CSL, but has not been included in the phylogeny by Mitchell and Heenan (2002), although it was mentioned as closely related to coastal Chilean species belonging to Sect. Edwardasia that also includes species from the Pacifi c islands and New Zealand (Crowder 1982;Peña et al. 2000). Sphaeralcea. Th is genus has ca. 40 herbaceous and shrubby species occurring in temperate parts of the Americas (Krapovickas 1965(Krapovickas , 1970. Th e Sierras CSL endemic small shrub S. cordobensis has been included in the phylogeny of Tarassa by Tate and Simpson (2003). Sphaeralcea cordobensis is a diploid included in a polyphyletic assemblage with Tarassa and Nototriche; however the unique morphology and geographic distribution suggest the three genera are diff erent lineages (Tate and Simpson 2003). Tillandsia. Pan-American genus with ca. 550 species (Barfuss et al. 2005). Tillandsia xiphioides is widely distributed in southern South America, and was included in the analysis of Barfuss et al. (2005); it joined an Andean clade forming a polytomy and characterized by its rapid evolution (Barfuss et al. 2005: 347). Trichloris. Grass genus with 2 disjunct species distributed in north-central Argentina and Bolivia and Mexico and southern USA (Rúgolo and Molina 2012). Th e endemic T. plurifl ora f. macra has not been included in a molecular phylogeny.
Trichocline. Genus of 22 species, most of them in South America from southern Peru to central Argentina and Chile (Katinas et al. 2008), with 13 species in Argentina (Zuloaga et al. 2008). Trichocline plicata, endemic to the Sierras CSL, has not been included in molecular phylogenies; a widespread and related species, T. reptans, grows in sympatry. Tridens. Grass genus with 14 species distributed in tropical and temperate regions of the Americas; 3 species in Argentina . Th e Sierras CSL endemic T. nicorae has not been studied in molecular phylogenetic studies. Valeriana. Th is genus comprises ca. 350 species usually found in mountainous regions (Bell and Donoghue 2005), while 81 are found in Argentina (Kutschker 2008). Th e roughly 175 South American species form a clade suggesting the existence of a modern center of diversifi cation in the Andes Donoghue 2005, Bell et al. 2012). Neither of these works has included the Sierras CSL endemics V. ferax and V. stuckertii. Zephyranthes. Th is genus comprises about 65 Neotropical species. Th e molecular phylogeny of American Amaryllidaceae by Meerow et al. (2000) showed the genus as polyphyletic, with two well diff erentiated clades including South American taxa.
Zephyranthes longystila, the endemic species of Sierras CSL, was not included in this work.

Endemic taxa of Sierras CSL and widespread related taxa
A total of 28 taxa of the endemics of the Sierras CSL is sympatric with a widespread congener, or with one found close to the area (Table 4).

Recent origins of endemism in the Sierras CSL
Two main sources of evidence suggest that 46 taxa (ca 40.4%) of the endemics of the Sierras CSL are neoendemic taxa sensu Stebbins and Major (1965). Th e fi rst evidence arises from available molecular phylogenetic studies (Table 3), which show 10 taxa (11.24 %) included in clades with divergence times of ca. 5 Ma or less. Th e second source is the existence of sympatry between an endemic taxon of the Sierras and a widespread taxon of the same genus (Table 4). Acanthocalycium spinifl orum was included in the study by Hernandez-Hernandez et al. (2014), showing a divergence time of ca. 2.5 Ma. Ackerman et al. (2006) included Blumenbachia hieronymii in their phylogeny and it was resolved in a clade with B. insignis, which is widely distributed in southern South America. Eryngium agavifolium, included in the phylogeny by Calviño et al. (2008) joined in a well-supported clade with E. elegans, which is widely distributed in southern South America. Escallonia cordobensis was included in the phylogeny  (Sede et al. 2013: 173), which suggests that the group evolved realtively recently. Grindelia globularifolia shows a similar pattern in the phylogeny by Moore et al. (2012), grouped in a large polytomy with several widespread species. Th e phylogram of Gymnocalycium by Demaio et al. (2011) showed that G. saglionis is the fi rst branching taxon in the genus. Hernández-Hernández et al. (2014) showed that G. saglionis diverged ca. 5 Ma, and the clade including a species of the subgenus Scabrosemineum (G. guanchinense) -where many species of the Sierras CSL belong -diverged ca. 2.5 Ma. In Portulaca, the phylogeny by Ocampo and Columbus (2011) set a divergence time for P. confertifolia of ca. 3 Ma. Prosopis campestris was included in the chronogram of Catalano et al. (2008), with a divergence time of ca. 1.8 Ma. Sphaeralcea cordobensis was included in the phylogeny by Tate and Simpson (2003), forming a clade with the widely distributed S. crispa. Tillandsia xiphioides has been included in the molecular phylogeny of Barfuss et al. (2005), who suggested all taxa of Tillandsia to be phylogenetically young, as inferred by the low genetic divergence. Tillandsia xiphioides var. minor was a member of a polytomy in their phylogenetic reconstruction, suggesting that it had not time to undergo a complete diff erentiation. Th e second source of supporting evidence is the existence of pairs of taxa with the endemic species of Sierras CSL occurring in sympatry or parapatry with a widespread congeneric species. Walck et al. (2001) compared Solidago shortii Torr. & A.Gray, a narrow endemic species of eastern North America, with S. altissima L., a widespread species, and found that S. altissima is a better competitor than S. shortii because of its greater height, larger leaf area and more extensive clonal growth. On the other hand, S. shortii tolerates drought stress better than S. altissima because the allocation of a higher percentage of biomass to roots, higher root/shoot ratio and greater capacity to maintain leaf turgor under xeric conditions. As a consequence of the diff erences in these traits, and although the lack of a molecular phylogenetic framework precludes conclusive classifi cation, Walck et al. (2001) suggested the endemic taxon to be probably derived from the widespread one.
Th ese aspects of the endemics of the Sierras (inclusion in clades and sympatry with a widespread congeneric taxon) are congruent with the geological and biological history of the region. Th e Sierras CSL system is the result of a ca. 520 Ma (Paleozoic) orogenic process that around 399 Ma was subject to an intrusion of magmatic batholiths (Baldo et al. 1996). Th e current arrangement, with blocks of basement tilted eastwards, is the result of the Andean orogeny, which rejuvenated the whole region in the Miocene-Pliocene, starting at ca. 5.3 Ma (Baldo et al. 1996). Th e actual composition of the vegetation of the Sierras CSL would have been assembled during this later interval, and has probably been preceded by times of major interchange with neighboring areas (Prado 1993a).

Altitudinal distribution of endemic taxa
Th e distribution of endemic taxa varied among the altitudinal belts. In a chorological study on 20 selected sites of the Sierras CSL, Cabido et al. (1998) emphasized that the upper vegetation belt in the Sierras CSL is distinct not only because its richness in Andean phytogeographic elements, but also due to the occurrence of highly restricted endemics. Th e data presented here show that the altitudinal belt with highest number of endemic taxa is the lowest (the sierra forest belt) with 35 endemic taxa, while the upper (the high-altitude grasslands and woodlands) has 11 endemic taxa (Fig. 2,  Table 2). Th e cumulative number of endemic taxa in the two lower belts suggests that diff erentiation and establishment of neoendemic taxa occurred most probably in the lower vegetation belts of the Sierras CSL, which have clear fl oristic affi nities with surrounding Chaco vegetation (Prado et al. 1993a(Prado et al. , 1993bCabido et al. 1998).

Conclusion
Why more studies on local endemics are needed Our data suggests that many endemic taxa of the Sierras de Córdoba and San Luis have developed as consequence of diff erentiation processes occurred during the last approximately 7 Ma. Likewise, the whole fl ora of the Sierras has been only partially isolated from surrounding Chaco vegetation. Th e overall lower presence of endemic taxa of the Sierras in phylogenetic studies emphasizes the need for their inclusion in such studies as a mean to achieve a better understanding of the evolutionary and biogeographical history of this area. Lastly, the present work also suggests that, although extracting information on speciation from phylogenies is not straightforward (Barraclough and Nee 2001), including endemic taxa in phylogenetic studies could provide useful insights on evolution of endemism and areas of endemism. Although our analysis is specifi cally aimed at a defi ned geographic area, the concept of analyzing all the endemic taxa of a particular zone could reveal patterns of biodiversity, since endemic taxa richness is a product of the interaction between historical processes as speciation or migration and contemporary factors as ecology or landscape use.