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

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?

‘The 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 effects which they produced on the development of the flora and the vegetation’ (Braun-Blanquet 1923: 223). Although many studies have dealt with the origin, classification 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 definitions last through time. The study of plant endemism is important because it could improve our knowledge of the flora of a region in at least two different respects, which are briefly discussed below.

Biogeography and evolution

The first aspect, perhaps the most traditional, has to do with biogeography and evolution of plants. The work of Stebbins and Major (1965) on the endemics of California outlined PageBreakthe basic elements to analyze when dealing with the endemic flora of a region: a) the floristic affinities 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 differentiate paleo- from neo-endemism.

These 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).

The concepts of floristic affinities 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 influence 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 definition 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 offer 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) defined 25 major biodiversity hotspots, and some have been well studied, e.g. the Brazilian Atlantic forest (Tabarelli et al. 1999, Morellato and Haddad 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 differentiation in plant populations (Kruckeberg and Rabinowitz 1985; Lesica et al. 2006). The Sierras of Córdoba and San Luis (“Sierras CSL”) represents such an area, extending ca. 550 km in NE-SW length and about PageBreak110 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 northeast-southwest 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).

Figure 1.

Map of the Sierras of Córdoba and San Luis (Sierras CSL).

Biogeographically, the flora 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 finally, the altitude grasslands and woodlands, from 1700 meters upwards (Fig. 2). The upper belt is floristically different from the other two and shows affinities with Andean and Patagonian floristic 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 fires and livestock grazing (Cingolani et al. 2013).

Figure 2.

Vegetation belts in Sierras CSL.

Representative endemic taxa of the Sierras CSL. (Clockwise) , , , , , , , .

The implementation of conservation strategies needs in the first 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 specific evaluation of the endemic taxon richness of the Sierras CSL has not been done, we compiled a critical list of all species and infraspecific 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, specifically 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 verified both the endemic status and the distribution of each taxon restricted to the Sierras CSL as defined 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). Verification 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 affect 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 floristics of the Sierras CSL has been well studied (Cabido et al. 1987, 1998; Giorgis 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 and Gutierrez 2006). We list 89 taxa (69 species and 20 infraspecific 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. The genus with the most endemics is , with 16 taxa. , , , , , , and have 3 endemic taxa; , , , , and have 2 endemic taxa and the remaining genera each have one taxon.

Table 1.

List of endemic species and infraspecific taxa of the Sierras of Córdoba and San Luis. Distribution by Province D: Córdoba: 1; San Luis: 2; Santiago del Estero: 3. Life Form LF: A-annual herb; P-perennial herb; S-shrub; SL-shrublet; V-perennial vine; SU-succulent, E-epiphytic.

	Family	Species	D	Elevation	LF
1	Alliaceae	Nothoscordum achalense Ravenna	1	1000–1800	P
2	Amaranthaceae	Alternanthera pumila O Stützer	1	1000–2000	P
3	Amaranthaceae	Gomphrena colosacana Hunz. & Subils var. andersonii Subils & Hunz.	2	500–1000	SL
4	Amaranthaceae	Gomphrena pulchella Mart. subsp rosea (Griseb.) Pedersen	1,2	500–1000	P
5	Amaranthaceae	Gomphrena pulchella Mart. var. bonariensis (Moq.) Pedersen	2	0 - 500	P
6	Amaryllidaceae	Habranthus sanavirone Roitman, A. Castillo, G. Tourn. & Uria	1	700–900	P
7	Amaryllidaceae	Zephyranthes longistyla Pax	1, 2, 3	1000–1500	P
8	Apiaceae	Eryngium agavifolium Griseb.	1, 2, 3	500–1000	P
9	Asteraceae	Grindelia cabrerae Ariza var alatocarpa Ariza	1	0–500	SL
10	Asteraceae	Grindelia globularifolia Griseb.	1	2000–2200	SL
11	Asteraceae	Helenium argentinum Ariza	1, 2, 3	200–1000	P
12	Asteraceae	Hieracium achalense Sleumer	1, 2	1000–2200	P
13	Asteraceae	Hieracium cordobense Sleumer	1, 2	1000–2000	P
14	Asteraceae	Hieracium criniceps Sleumer	1	1500–3000	P
15	Asteraceae	Hypochaeris caespitosa Cabrera	1, 2	1000–2500	P
16	Asteraceae	Hysterionica dianthifolia (Griseb.) Cabrera var dianthifolia	1	2000–3000	SL
17	Asteraceae	Hysterionica dianthifolia (Griseb.) Cabrera var pulvinata (Cabrera) Ariza	1	2000–2500	SL
18	Asteraceae	Isostigma cordobense Cabrera	1	500–1000	SL
19	Asteraceae	Mutisia castellanosii Cabrera var comechingoana Ariza	1	0–500	V
20	Asteraceae	Senecio achalensis Cabrera	1	1700–2800	SL
21	Asteraceae	Senecio fragantissimus Tortosa & A.Bartoli	2	800	S
22	Asteraceae	Senecio retanensis Cabrera	1, 2	2200–2800	SL
23	Asteraceae	Soliva triniifolia Griseb.	1		A
24	Asteraceae	Trichocline plicata Hook. & Arn.	1, 2	1000–3000	P
25	Berberidaceae	Berberis hieronymi C.K.Schneid	1	1000–2000	S
26	Brassicaceae	Mostacillastrum carolinense (Scappini, C.A.Bianco & Prina) Al-Shehbaz	2	1500–1700	SL
27	Bromeliaceae	Tillandsia xiphioides Ker Gawl. var. minor L.Hrom.	1, 2	1000–1500	E
28	Cactaceae	Acanthocalycium spiniflorum (K Schum) Backeb.	1, 2	1000–1500	SU
29	Cactaceae	Gymnocalycium achirasense H.Till & Schatzl ex H.Till	1, 2	500–1000	SU
30	Cactaceae	Gymnocalycium andreae (Boed) Backeb	1	1500–2500	SU
31	Cactaceae	Gymnocalycium bruchii (Speg) Hosseus	1, 2	1000–2000	SU
32	Cactaceae	Gymnocalycium calochlorum (Boed) Y.Itô	1	500–1500	SU
33	Cactaceae	Gymnocalycium capillense (Schick) Hosseus	1	500–1500	SU
34	Cactaceae	Gymnocalycium carolinense (Neuhuber) Neuhuber	2	1500–2000	SU
35	Cactaceae	Gymnocalycium castellanosii Backeb. subsp. ferocius (H.Till & Amerhauser) Charles	1	500–700	SU
36	Cactaceae	Gymnocalycium erinaceum J.G.Lamb.	1	500–1500	SU
37	Cactaceae	Gymnocalycium gibbosum (Haworth) Pfeiffer ex Mittler subsp. borthii (Koop ex H.Till) Charles	2	500–800	SU
38	Cactaceae	Gymnocalycium horridispinum Frank ex H.Till	1	500–700	SU
39	Cactaceae	Gymnocalycium monvillei (Lem) Britton & Rose	1, 2	500–2000	SU
40	Cactaceae	Gymnocalycium mostii (Gürke) Britton & Rose subsp. mostii	1	500–1000	SU
41	Cactaceae	Gymnocalycium mostii (Gürke) Britton & Rose subsp. valnicekianum (Jajó) Meregalli & Charles	1	500–1000	SU
42	Cactaceae	Gymnocalycium neuhuberi H.Till & W.Till	2	500–1500	SU
43	Cactaceae	Gymnocalycium quehlianum (F Haage ex Quehl) Vaupel ex Hosseus	1	500–1000	SU
44	Cactaceae	Gymnocalycium robustum R Kiesling, O.Ferrari & Metzing	1	0–500	SU
45	Campanulaceae	Siphocampylus foliosus Griseb. var. glabratus E.Wimm	1	1000–1500	SL
46	Campanulaceae	Siphocampylus foliosus Griseb. var. minor Zahlbr.	1	500–1500	SL
47	Campanulaceae	Siphocampylus lorentzii E.Wimm.	1	500–1500	SL
48	Caryophyllaceae	Cerastium argentinum (Pax) F.N.Williams	1		P
49	Cyperaceae	Carex monodynama (Griseb.) G.A.Wheeler	1	2600–2900	P
50	Escalloniaceae	Escallonia cordobensis (Kuntze) Hosseus	1, 2	1000–2500	S
51	Fabaceae	Adesmia cordobensis var appendiculata Ulibarri & Burkart	2	900–1100	SL
52	Fabaceae	Apurimacia dolichocarpa (Griseb.) Burkart	1	1800–3000	S
53	Fabaceae	Astragalus parodii I.M.Johnst.	1	1000–2500	P
54	Fabaceae	Mimosa cordobensis Ariza	1	0–500	S
55	Fabaceae	Prosopis campestris Griseb.	1, 2	500–2000	S
56	Fabaceae	Sophora linearifolia Griseb.	1, 2	1000–1500	SL
57	Gencianaceae	Gentianella parviflora (Griseb) T.N.Ho	1	1500–2500	A
58	Geraniaceae	Geranium parodii I.M.Johnst.	1, 2	1800–2600	P
59	Iridaceae	Calydorea undulata Ravenna	1	800–1000	P
60	Loasaceae	Blumenbachia hieronymi Urb.	1, 2	1900–2500	A
61	Malvaceae	Sphaeralcea cordobensis Krapov.	1, 2, 3	500–1000	SL
62	Orchidaceae	Aa achalensis Schltr.	1, 2	1500–2500	P
63	Plantaginaceae	Plantago densa (Pilg.) Rahn	1, 2	100–1800	P
64	Poaceae	Aristida minutiflora Caro var. glabriflora Caro	1, 2	500–1000	P
65	Poaceae	Aristida multiramea Hack.	1, 2	0–1000	P
66	Poaceae	Aristida sayapensis Caro	2	500–1000	P
67	Poaceae	Cenchrus rigidus (Griseb.) Morrone	1, 2	100–800	P
68	Poacaeae	Danthonia melanathera (Hack.) Bernardello	1, 2	1200	P
69	Poacaeae	Melica decipiens Caro	1, 2	1500–200	P
70	Poaceae	Nassella hunzikeri (Caro) Barkworth	1, 2	900–1500	P
71	Poaceae	Nassella nidulans (Mez.) Barkworth	1, 2	500–1500	P
72	Poaceae	Nassella stuckertii (Hack.) Barkworth	1	500–1500	P
73	Poaceae	Poa hubbardiana Parodi	1, 2	1400–2100	P
74	Poaceae	Poa stuckertii (Hack.) Parodi	1, 2	500–1500	P
75	Poaceae	Trichloris pluriflora E. Fourn. f. macra Hack.	1	500–1100	P
76	Poaceae	Tridens nicorae Anton	1, 2	1500	P
77	Portulacaceae	Portulaca confertifolia Hauman var. cordobensis D.Legrand	1, 2	500–1000	P
78	Portulacaceae	Portulaca obtusifolia D. Legrand var. obtusifolia	1	0–500	P
79	Portulacaceae	Portulaca ragonesei D.Legrand	1	200–400	P
80	Rosaceae	Geum brevicarpellatum F.Bolle	1	500–1500	P
81	Rubiaceae	Borreria eryngioides Cham & Schltdl. var. ostenii (Standl.) E.L.Cabral & Bacigalupo	1, 2	500–1000	P-SL
82	Rubiaceae	Richardia coldenioides Rusby	1	2700	P
83	Solanaceae	Solanum concarense Hunz.	2	500–1000	P
84	Solanaceae	Solanum ratum C.V.Morton	1	0–1000	P
85	Solanaceae	Solanum restrictum C.V.Morton	1	500–1500	P
86	Valerianaceae	Valeriana ferax (Griseb) Höck	1	2100–2300	P
87	Valerianaceae	Valeriana stuckertii Briq.	1, 2	1000–2500	P
88	Verbenaceae	Junellia bisulcata (Hayek) Moldenke var. campestris (Griseb.) Botta	1, 3	1000–2000	S
89	Verbenaceae	Parodianthus capillaris Tronc.	1	0–500	S

Checklist of the endemic taxa of the Sierras of Córdoba and San Luis

All vouchers listed are from Argentina. Province (Córdoba, San Luis or Santiago de Estero) and Departamento (Depto.) are detailed for each where data are available.

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Voucher: Romanutti, A. 198, Prov. Córdoba, Depto. Punilla, Quebrada del Condorito, en el sendero hacia la Quebrada,

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Voucher: Lorentz, P. G. 697, Prov. Córdoba, (B)

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Distribution of the endemic taxa

The altitudinal distribution of the endemic taxa in the Sierras CSL is shown in Table 2 and Fig. 2. There 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. The 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.

Table 2.

Summary of altitudinal distribution of endemic taxa in the Sierras CSL. Taxa identification numbers as in Table 1.

Vegetation belt or combination	lower	middle	upper	lower/middle	middle/upper	lower/middle/upper
taxa	35	2	11	17	7	17
percentage	39.32	2.29	12.35	19.54	8.04	19.54
taxa ID	3, 4, 5, 7, 8, 17, 18, 20, 28, 34, 36, 37, 39, 40, 41, 42, 47, 49, 52, 57, 61, 64, 65, 66, 67, 68, 75, 77, 78, 79, 81, 82, 83, 84, 89	25, 76	9, 15, 16, 19, 21, 22, 47, 50, 56, 60, 86	6, 10, 26, 27, 31, 32, 35, 43, 44, 45, 54, 70, 71, 72, 74, 80, 85	13, 29, 33, 55, 62, 69, 73	1, 2, 11, 12, 14, 23, 24, 30, 38, 48, 51, 53, 58, 59, 63, 87, 88

Phylogenetic knowledge of the endemic taxa of the CSL Sierras

The 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: , , , , , , , , and (Table 3).

Table 3.

Phylogenetic knowledge of the endemic taxa of the CSL Sierras.

Family	Genus	Phylogeny of the genus including endemic species of CSL Sierras
Amaranthaceae	Gomphrena	Moore et al. 2012
Apiaceae	Eryngium	Calviño et al. 2008
Bromeliaceae	Tillandsia	Barfuss et al. 2005
Cactaceae	Acanthocalycium	Schlumpberger and Renner 2012
Cactaceae	Gymnocalycium	Demaio et al. 2011
Escalloniaceae	Escallonia	Sede et al. 2013
Fabaceae	Prosopis	Catalano et al. 2007
Loasaceae	Blumenbachia	Hufford et al. 2005; Ackerman et al. 2006
Malvaceae	Sphaeralcea	Tate and Simpson 2003
Portulacaceae	Portulaca	Ocampo and Columbus 2012

Assessment of the phylogenetic knowledge of the genera with endemic taxa of the Sierras CSL.

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).

Table 4.

Sympartry/parapatry of endemic taxa of Sierra CSL and widespread congeners.

Endemic taxa Sierra CSL	Widespread related taxa	Source
Adesmia cordobensis var. appendiculata	Adesmia cordobensis Burkart	Zuloaga and Morrone 1999
Alternanthera pumila	Alternanthera pungens Kunth	Zuloaga and Morrone 1999
Aristida minutiflora var. glabriflora	Aristida minutiflora Caro	Zuloaga and Morrone 1999
Blumenbachia hieronymi	Blumenbachia insignis Schrad.	Hufford et al. 2005, Ackerman et al. 2006
Borreria eryngioides var. ostenii	Borreria eryngioides Cham. & Schltdl.	Zuloaga and Morrone 1999
Calydorea undulata	Calydorea pallens Briseb.	Zuloaga and Morrone 1999
Eryngium agavifolium	Eryngium elegans Cham. & Schltdl.	Calviño et al. 2008
Escallonia cordobensis	Escallonia petrophila Rambo & Sleumer, Escallonia ledifolia Sleumer, Escallonia farinacea A. St.-Hil., Escallonia bifida Link & Otto, Escallonia laevis (Vell.) Sleumer, Escallonia hypoglauca Herzog and Escallonia tucumanensis Hosseus	Sede et al. 2013
Geranium parodii	Geranium sessiliflorum Cav.	Aedo et al. 2005
Gomphrena pulchella subsp. rosea	Gomphrena pulchella Mart.	Borsch 2008
Grindelia cabrerae var. alatocarpa	Grindelia cabrerae Ariza	Zuloaga and Morrone 1999
Grindelia globularifolia	Gomphrena pulchella Mart.	Moore et al. 2012
Habranthus sanavironae	Habranthus robustus Herb. ex Sweet	Roitman et al. 2007
Junellia bisulcata var. campestris	Junellia bisulcata (Hayek) Moldenke	O’Leary 2009
Mutisia castellanosii var. comechingoana	Mutisia castellanosii Cabrera	Zuloaga and Morrone 1999
Nassella stuckertii	Nassella tenuissima (Trin.) Barkworth	Cialdella 2012
Parodianthus capillaris	Parodianthus illicifolium (Moldenke) Tronc.	Marx et al. 2010
Portulaca confertifolia	Portulaca eruca Hauman, Portulaca perennis R.E. Fr., Portulaca mucronulata D. Legrand, Portulaca obtusa Poelln. and Portulaca gilliesii Hook.	Ocampo and Columbus 2011
Prosopis campestris	Prosopis chilensis (Molina) Stuntz emend. Burkart	Catalano et al. 2008
Siphocampylus foliosous var. glabratus; Siphocampylus foliosus var. minor	Siphocampylus foliosus Griseb.	Zuloaga and Morrone 1999
Solanum concarense, Solanum ratum, Solanum restrictum	Solanum salicifolium Phil.	Knapp 2013
Soliva triniifolia	Soliva anthemifolia (Juss.) Sweet	Zuloaga and Belgrano 2008
Sphaeralcea cordobensis	Sphaeralcea crispa Baker f.	Tate and Simpson 2003
Tillandsia xiphioides var. minor	Tillandsia xiphioides Ker Gawl.	Zuloaga and Morrone 1999
Trichloris pluriflora fo. macra	Trichloris pluriflora E. Fourn.	Rúgolo and Molina 2012
Trichocline plicata	Trichocline reptans (Wedd.) Hieron.	Zuloaga and Belgrano 2008

Discussion

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 PageBreakPageBreaksensu Stebbins and Major (1965). The first 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. The second source is the existence of sympatry between an endemic taxon of the Sierras and a widespread taxon of the same genus (Table 4). 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 in their phylogeny and it was resolved in a clade with , which is widely distributed in southern South America. , included in the phylogeny by Calviño et al. (2008) joined in a well-supported clade with , which is widely distributed in southern South America. was included in the phylogeny by Sede et al. (2013), forming an unresolved clade with , , , and , and . All these species are barely differentiated (Sede et al. 2013: 173), which suggests that the group evolved realtively recently. shows a similar pattern in the phylogeny by Moore et al. (2012), grouped in a large polytomy with several widespread species. The phylogram of by Demaio et al. (2011) showed that is the first branching taxon in the genus. Hernández-Hernández et al. (2014) showed that diverged ca. 5 Ma, and the clade including a species of the subgenus () - where many species of the Sierras CSL belong - diverged ca. 2.5 Ma. In , the phylogeny by Ocampo and Columbus (2011) set a divergence time for of ca. 3 Ma. was included in the chronogram of Catalano et al. (2008), with a divergence time of ca. 1.8 Ma. was included in the phylogeny by Tate and Simpson (2003), forming a clade with the widely distributed . has been included in the molecular phylogeny of Barfuss et al. (2005), who suggested all taxa of to be phylogenetically young, as inferred by the low genetic divergence. was a member of a polytomy in their phylogenetic reconstruction, suggesting that it had not time to undergo a complete differentiation.

The 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 Torr. & A.Gray, a narrow endemic species of eastern North America, with L., a widespread species, and found that is a better competitor than because of its greater height, larger leaf area and more extensive clonal growth. On the other hand, tolerates drought stress better than 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 differences in these traits, and although the lack of a molecular phylogenetic framework precludes conclusive classification, Walck et al. (2001) suggested the endemic taxon to be probably derived from the widespread one.

These 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. The 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). The 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). The 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

The 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. The 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). The cumulative number of endemic taxa in the two lower belts suggests that PageBreakdifferentiation and establishment of neoendemic taxa occurred most probably in the lower vegetation belts of the Sierras CSL, which have clear floristic affinities with surrounding Chaco vegetation (Prado et al. 1993a, 1993b; Cabido 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 differentiation processes occurred during the last approximately 7 Ma. Likewise, the whole flora of the Sierras has been only partially isolated from surrounding Chaco vegetation. The 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 specifically aimed at a defined 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.