Survey of the vascular plants of Sierra Chica , the untouched area of the Paititi Natural Reserve ( southeastern Tandilia mountain range , Buenos Aires province , Argentina )

The Paititi Natural Reserve is located in the southeastern part of the Tandilia mountain range (Buenos Aires province, Argentina). With the aim of recording the floristic richness of Sierra Chica, an untouched area of the reserve, all vascular plants were inventoried and categorized by family, status, and life form. Altogether, 364 taxa from 72 families were found, with the most predominant families being Poaceae (20.7%), Asteraceae (20.1%), and Fabaceae (5.8%). We found 95 adventive species, 4 cosmopolitan, and 265 native. The most abundant life forms were hemicryptophytes (33.1%), therophytes (30.6%), and criptophytes (22.6%); the therophytes were mostly represented by adventive species. We also found species that were known from Buenos Aires province but not from mountainous areas. Despite being a small area within Argentina, Sierra Chica constitutes a valuable refuge for native flora of the Tandilia mountain range system, which is in danger of being affected by exotic plants.


Introduction
In the last decades, agricultural intensification (Benton et al. 2003) and urban and rural population growth (MEA 2005) have been the main causes of biodiversity decline in agricultural landscapes (Krebs et al. 1999).Fire, habitat fragmentation, introduction of exotic species, and high rates of agrochemical application have generated negative impacts on different habitats, and therefore, on the diversity of plants and animals (Frangi et al. 1980;Tscharntke et al. 2005).The province of Buenos Aires, located in the east-central region of Argentina, due to the advance of the farming frontier, does not escape this phenomenon (Bilenca and Miñarro 2004, Paruelo et al. 2005, Viglizzo et al. 2011).However, the Tandilia and Ventania mountain range systems disrupt the typical plain landscape of the province, limiting the extent of agricultural fields, and acting as biodiversity reservoirs (Fig. 1).The rocky outcrops are known hotbeds of biodiversity that allow refuge for native, endemic, and threatened species, and contribute to the conservation of these species (OPDS 2011, Cantero et al. 2014, Kristensen et al. 2014).In this regard, Bertonatti and Corcuera (2000) considered the mountain ranges as areas of outstanding biodiversity, and Bilenca and Miñarro (2004) highlighted that in Buenos Aires province, 67% of the vascular species with conservation priority can be found in Tandilia and Ventania mountain range systems.
The available information on the flora of the Tandilia system, (Frangi 1975, Valicenti et al. 2005, Escaray 2007, Alonso et al. 2009a, Kristensen et al. 2014), part of Azul, Tandil, and Balcarce counties, highlights the great value of the floristic richness (mainly native and endemic taxa) of these mountains.The Tandilia system consists of mountain ranges interrupted by valleys, which extend 350 km from the center of Buenos Aires province to its southeastern Atlantic coast (Fig. 1).Available data from surveys, herbarium materials, and floristic inventories, include 578 species and infraspecific taxa for this area (Alonso et al. 2009b).However, this number is preliminary and could substantially increase if the mountain ranges that have not been fully inventoried were studied, such as those belonging to southeast extremity of this orographic system.The Tandilia system, near Mar del Plata, is affected by anthropogenic disturbances including farming, recreational activities, infrastructure projects, and natural resource extraction, such as mining and collection of medicinal and ornamental plants.Such alterations can cause the disappearance of native or even endemic species, their replacement by foreign floristic elements and the reduction of the ecosystem services associated with these environments (Méndez 2009, OPDS 2011, Álvarez et al. 2012, Kristensen et al. 2014, Sanhueza and Zalba 2014, Echeverría et al. 2015).Because of this, it is useful to assess the biodiversity, level of endemism, and degree of degradation of southeastern Tandilia mountain range.
Estancia Paititi is a farm in the southeastern Bue-nos Aires province that has been considered a valuable grassland area (Bilenca and Miñarro 2004) and an area of interest for conservation and ecotourism (Chebez 2005).Estancia Paititi is divided into 2 areas: 1 of them has deep fertile soils and is dedicated to organic farming (crops and pastures), while the other has 2 rocky outcrops and is a natural reserve (Paititi Natural Reserve).The objectives of this reserve are to work actively towards the conservation and research of natural and cultural resources and to raise awareness of the care of the environment.Since 2014, Paititi Reserve is a member of the Argentine Network of Private Natural Reserves (RARNAP 2016).The reserve was divided in 2 areas, Sierra Grande, dedicated to educational, recreational, and livestock activities, and Sierra Chica, which remains untouched, with minimal anthropic interference.The latter area is set aside for research on archeology, zoology, and botany (Fig. 1).A thorough knowledge of the flora of this reserve is essential to quantify floristic richness and to develop guidelines for future studies and conservation programs.With this aim, a floristic survey of Sierra Chica, the untouched area of Paititi Natural Reserve, was done.

Methods
Study site.Paititi Natural Reserve (37°54′00′′ S, 057°49′00″ W; geodetic datum WGS84) is located at the southeast edge of La Peregrina mountain range, General Pueyrredón county, Buenos Aires province, Argentina.These rocky outcrops belong to the Tandilia mountain range system that traverses the province of Buenos Aires from its center to the southeast (Fig. 1).The mountains are mainly composed by orthoquartzites from the Lower Paleozoic, established over a Precambrian crystalline basement (Teruggi and Kilmurray 1980).Surrounding these mountains, the soil matrix is formed by various The area surrounded by a red line corresponds to the Paititi Natural Reserve while the area surrounded with a dotted white line corresponds to "Sierra Chica".Satellite image obtained from Sentinel Playground (Sentinel Playground, 2017).
geological materials resulting from loess deposition during the late Cenozoic.The reserve is located in the Pampeana Phytogeographical Province (Pampeano Austral District), which is characterized by the presence of a climax grassland community (Bothriochloa laguroides, Nassella neesiana, Jarava plumosa, Piptochaetium montevidense and Aristida murina), bunches of Tussock Paspalum (Paspalum quadrifarium), and shrubs (Baccharis dracunculifolia ssp.tandilensis, Colletia paradoxa, and Dodonaea viscosa) (Cabrera and Zardini 1978).The climate is subhumid-humid, temperate-cold in winter and temperate-warm in summer, with a mean annual temperature of 14 °C, and with maximum temperatures reaching 32 °C, and minimum temperatures around 0 °C.In winter, frosts occur and sometimes it snows.The annual rainfall is around 850 mm and although the rains are distributed throughout the year, they are most intense in winter and scarce during the summer (Falasca et al. 2000, INTA 2016).The Paititi reserve covers an area of 220 ha (RARNAP 2016) of which 40 ha are part of Sierra Chica.This is a rocky outcrop separated from Sierra Grande by a watercourse that originates in the hills of an adjoining property and whose route is accompanied by an arboreal stratum.Sierra Chica has an altitudinal range of 88 to 156 m above sea level.The summits and upper slopes of this mountain are variously shaded and with variable soil depth, ranging from shallow (<10 cm) to deep (> 60 cm).Deep soils allow the growth of trees and shrubs (Fig. 2).

Data collection and analysis.
A thorough survey of vascular plants was made from December 2013 to June 2015 in Sierra Chica.Surveys were held every 2-3 weeks from spring to autumn, and every 4 weeks in winter, covering the periods of flowering and fructification of the different plant entities.After collecting reference plant material, the specimens were identified based on the following: Flora de la provincia de Buenos Aires (Cabrera 1963(Cabrera , 1965a(Cabrera , 1965b(Cabrera , 1967(Cabrera , 1968(Cabrera , 1970)), Flora Rioplatense (Hurrell 2009a(Hurrell , 2013)), and Flora Argentina (Al-Shehbaz and Salariato 2012, Múlgura et al. 2012, Zuloaga et al. 2012a, 2012b, Barboza 2013, Zuloaga et al. 2014a, 2014b).The vascular plants were classified into subclasses and superorders following Chase and Reveal (2009).Families within subclasses and superorders were according to Christenhusz et al. (2011aChristenhusz et al. ( , 2011b) ) for fern and gymnosperms, respectively, and the classification system of The Angiospermae Phylogenetic Group IV (2016), for the angiosperms.Species names were updated based on the Flora Argentina database (http://www.floraargentina.edu.ar/).This database was also used to determine species' status as native (species naturally occurring in the area), adventive (exotic species, with natural introduction or mediated by humans), and cosmopolitan (species that are widely distributed).Within native category, species were classified in 3 groups according to their distribution range: species of wide distribution in the American continent, species exclusively of the Southern Cone Region of South America, and species endemic to mountain ranges of Buenos Aires province (Flora Argentina 2017).Species were also classified according to their type of habitat (terrestrial, aquatic floating, and aquatic marshy) and life form (therophytes, hemicryptophytes, cryptophytes, chamaephytes, lianas, epiphytes, and phanerophytes) (Raunkiaer 1934).Those species that were considered to be threatened by Delucchi (2006), according to the IUCN Red List Categories and Criteria, were noted.Reference specimens were deposited in the BAL Herbarium (E.E.A. Balcarce, Instituto Nacional de Tecnología Agropecuaria Balcarce, Buenos Aires, Argentina).
Forty-two species were described; these include 1 species with an uncertain identification, others that are newly recorded in Buenos Aires mountain ranges, and the rest that are native species (including endemic species) that, according to Delucchi (2006), are threatened.However, those newly recorded species that are frequently described in the literature as alien or native weeds, ornamental trees, fruit shrubs, forage plants, or typical members of watercourses or ponds of the province are not described.

Results
Identified taxa in the inventoried area of Paititi Natural Reserve are presented in Table 1.Some species were only found in specific sites of the reserve, while others were found in many different sites.The location where each species was more frequently found is described in Fig. 3 and detailed in Tables 1 and 2. In the untouched area the richness of vascular plants reached 364 species and infraspecific taxa.In the untouched area the richness of vascular plants reached 360 species and 4 species were represented by 2 varieties each (Conyza bonariensis, C. sumatrensis, Echinochloa crus-galli, and Poa ligularis).
Regarding the geographic origin of the species and the infraspecific taxa, 1.1% were cosmopolitan, 26.1% were adventive, and 72.8% were native (Fig. 4).Within this last group, 187 species grow in several places of the American continent, 78 species occur exclusively in the Southern Cone Region of South America (Flora Argentina 2017), and only 7 species are endemic to mountain ranges of Buenos Aires province (Table 1).From the total number of taxa, 30.6% were annual or biennial plants (therophytes), while 69.4% were perennial species.Among the perennial species, the most abundant life forms were hemicryptophytes (33.1%) and cryptophytes (22.6%).Lianas and epiphytes phanerophytes, chamaephytes, and phanerophytes were scarce (1.1%, 6.1%, 6.6%, respectively).Each life form was mainly represented by species of native status, except for therophytes, most of which were adventive (Fig. 4).
Diagnoses, descriptions, and images are presented for 1 species that was not fully identified, 10 species that  were newly recorded in Buenos Aires mountain ranges, and 31 native species, mostly threatened according to Delucchi (2006).Cryptophyte, native with wide distribution in the American continent.Least Concern (Delucchi 2006).
Comments.This is a rare species in the study area.This fern grows in shady, humid sites.At the summit, it grows in deep cracks of rocks and also along the shaded banks of the stream.The major difference between A. raddianum and A. chilense Kaulfuss, which is also frequent in Buenos Aires mountains, is in the shape of the pinnules; the latter species presents reniform pinnules without cuneate bases and with the upper margin entire or with short incisions.

Subclass Magnoliidae Superorder Lilianae
Order Asparagales: Family Amaryllidaceae: Tribe Gilliesiae Genus Nothoscordum Kunth Cryptophyte, native with distribution in the Southern Cone Region of South America; previosly known from the Entre Ríos and Corrientes provinces (Argentina) but not from Buenos Aires province.
Comments.This is a rare species in the study area.
It grows in full sunlight conditions on shallow to moderately deep, damp soils on rocky and grassy slopes with other small to medium-sized species.Nothoscordum gaudichaudianum can be distinguished from other Nothoscordum species by its erect peduncles, white tepals, free filaments, and bulbs with characteristic onion odor.Cryptophyte, native with distribution in the Southern Cone Region of South America; previously recorded from Buenos Aires province but not from mountainous areas.

Nothoscordum montevidense
Characteristics.Perennial herb, 5-10 cm tall.Bulb solitary, globose, ca 1 cm in diameter.Sheaths short.Leaves to 10 cm long, parallel-veined, linear, with apex acute.Peduncles erect.Inflorescence: an umbel, with 2-10 flowers.Tepal perianth yellow, 3.5-5 mm long.Anthers to 2 mm long.Fruit: a capsule.Comments.This is an infrequent species in the study area.It grows in shallow to moderately deep, damp soils on rocky and grassy slopes with other white-flowered Nothoscordum species.Cabrera (1968) reported N. montevidense from Buenos Aires province but not this subspecies.Hurrell (2009b) reported the existence of 3 subspecies in the Rioplatense region of northwestern Buenos Aires province.Our Paititi specimens belong to N. montevidensis ssp.latitepalum because they are relatively tall and present flowers with wide yellow tepals.
Comments.This is a rare species in the study area.It grows in full sunlight conditions in rock cracks on slopes.It is very similar to C. herbertii ssp.herbertii, but this last species presents vivid orange tepals and united filaments.
Genus Gelasine Herb.Cryptophyte, native with distribution in the Southern Cone Region of South America.
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions and deep to moderate deep soils on rocky and grassy slopes.Gelasine elongate is the only species of its genus known from Buenos Aires province, and it can be recognized by its folded leaves and blue tepals.
Comments.This is a frequent species in the study area.It grows in full sunlight conditions and shallow to moderately deep soils on rocky and grassy slopes.The specimens of the Paititi Reserve have fleshy roots and their filaments are grouped forming a column.The base of this column is covered with glands so it would correspond to Sisyrinchium platense I.M. Johnst.or S. pachyrhizum Baker (Cabrera 1968, Roitman andHurrell 2009).However, in S. platense the tepals are violet to pale blue, and in S. pachyrhizum they are vivid yellow with brown spots.As neither of the described species for Buenos Aires province present tepals with the colors seen in our specimens, we have not identified our material to species.Cryptophyte, native with distribution in the Southern Cone Region of South America.Vulnerable due to restricted habitat (Delucchi 2006).
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions in shallow soils on grassland slopes and on summits.Bipinnula pennicillata can be recognized from other Orchidaceae by its 1-flowered inflorescence and its large flowers with rhombic, succulent labellum and sepals without appendices.

Chloraea membranacea Lindley
Comments.This is a rare species in the study area.It grows in damp soils, in shady places under trees.Chloraea membranacea is the only species of Chloraea known from Buenos Aires province and is distinguished from other Orchidaceae by its folded, thickened, fleshy roots, and its inclined anthers.
Order Poales: Family Bromeliaceae: Tribe Tillandsieae Genus Tillandsia L. Epiphyte, native with distribution in the Southern Cone Region of South America.Vulnerable for reasons unknown (Delucchi 2006).
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions in cracks of rocks on summits, where it forms hanging clumps.It is the only species of the genus that has been found in the Tandilia mountain range system.It is the only lithomorphic species found in rocky outcrops and presents dense roots and leaves, multiflorous spikes and green to pink floral bracts and sepals, not reddish like T. aëranthos (Loisel) L. B. Smith.Therophyte, native with distribution in the Southern Cone Region of South America; previously reported from Buenos Aires province but not from mountainous areas.
Comments.This is an infrequent species in the study area.It grows in shallow soils and rock cracks on the sum- Hemicryptophyte, native with distribution in the Southern Cone Region of South America; previously known from Buenos Aires province but not from mountainous areas.Available information is inadequate to make a direct or indirect assessment of its risk of extinction (Data Deficient) (Delucchi 2006).
Characteristics: Perennial, caespitose species herbs, 15-60 cm tall.Young leaves are folded to rolled.Leaves parallel-veined, green, glabrous, to 30 cm long.Inflores-   Comments.This is a frequent species in the study area.It grows in shallow to moderately deep soils on slopes, in grasslands, and around the pond.It is similar to Danthonia cirrata Hack.& Arechav., which also has been found in the Paititi Reserve, but the lemma of the latter species has the lateral lobes longer than the undivided part.
Comments.This is a frequent species in the study area.It grows in shallow to moderately deep soils and in rock cracks on the summits and on rocky or grassy slopes.It is similar to M. brasiliana Ard.However, the latter species presents 11-17 mm long spikelets, which are longer than in M. rigida (Torres 1980, Zuloaga 2012b).
Cryptophyte, native with distribution in the Southern Cone Region of South America.Vulnerable, reasons unknown (Delucchi 2006).
Characteristics.Perennial, caespitose species, with erect to slightly stretched culms, up to 30 to 50 cm tall, with roots on basal nodes.Leaves parallel-veined, folded to convolute, green, pubescent, up to 15 cm long, with retrorse hairs and membranous ligule.Inflorescence: a linear, loose panicle with white, compressed, multiflorous spikelets; glumes unequal; lemma papery with retrorse hairs and palea with glabrous lower surface.Fruit: an elliptic caryopsis.
Comments.This is a frequent species in the study area.It grows in shallow to moderately deep soils and in rock cracks on summits and on rocky and grassy slopes.It is similar to M. rigida, which has also been found in the Paititi Reserve, but M. rigida has glabrous abaxial leaf surface.Cryptophytes, endemic to mountain ranges of Buenos Aires province.Vulnerable for reasons unknown (Delucchi 2006).
Comments.This is an infrequent species in the study area.It grows in shallow soils and in rock cracks on slopes and summits.It can be differentiated from other Poa species of the area by its caespitose, glaucouse foliage and by its conduplicate leaves with flabellate basal innovations, as in several Iris species.

Superorder Rosanae
Order Fabales: Family Fabaceae: Tribe Mimoseae Genus Mimosa L. Chamaephytes; native with distribution in the Southern Cone Region of South America.Vulnerable, reasons unknown (Delucchi 2006).
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions in cracks of rocks on the summits.In the mountains of the area, M. tandilensis Speg.can also be found but differs from M. rocae by presenting prickles on the stems and purplish pink flowers.
Order Fabales: Family Fabaceae: Tribe Vicieae Genus Lathyrus L.    Cryptophytes; native with distribution in the Southern Cone Region of South America.

Lathyrus hookeri Don
Characteristics.Perennial twining herb that turns black when it dries.Rhizomes and decumbent tetragone stems with 2 wings in upper stems.Leaves sessile or subsessile, pinnately compound, with 2 oval, slightly glaucous, mucronate leaflets with notable veins, 1-7 terminal tendrils, and wide sagittate stipules.Inflorescence: a raceme with 5-10 flowers of lilac to violet petals.Fruit: a linear and erect legume, which turns black at maturity.
Comments.This is a frequent species in the study area.It grows in intermediate to full sunlight, on slopes with moderately deep, damp soils.Many species of the genus Lathyrus thrive in the mountain ranges of this region.Lathyrus hookeri can be recognized by the presence of very short petioles (or even sessile leaves) and by its fruit that turns black when dried.In the Paititi Reserve, specimens with violet petals were found, which is typical, and specimens with white petals were also found that, according to Cabrera (1967), would correspond to L. hookeri Don f. albiflora (O.Kuntze) Burkart.Nowadays, L. hookeri f. albiflora is synonym of L. hookeri Don (Flora Argentina 2017).Besides the white flower specimens, plants with white keel and violet standard and wings were also found.This would be the first record of this variant of L. hookeri.Therophytes, native with wide distribution in the American continent; previously recorded from Buenos Aires province but not from mountainous areas.
Comments.This is an infrequent species in the study area.It grows in intermediate to full sunlight on slopes with moderately deep, moist soils.Lathyrus pusillus can be recognized from the many other Lathyrus species in the region by the presence of sagittate stipules and brown legumes that do not turn black when dry.
Therophytes, native with distribution in the Southern Cone Region of South America; previously recorded from Buenos Aires province but not from mountainous areas.
Comments.This is an infrequent species in the study area.It grows in shady sites under trees in damp soils on slopes.It differs from other Vicia species by the presence of solitary flowers (exceptionally 2) that are up to 4 mm long.
Comments.This is an infrequent species in the study area.It grows in intermediate and full sunlight on slopes and in grasslands in moderately deep, moist soils.This perennial species differs from other Vicia species by the presence of peduncle racemes with flowers smaller than 1.4 cm long, and pubescent leaves with 3-5 linearlanceolate to oblong pairs of leaflets.
Order Fabales: Family Polygalaceae: Tribe Polygaleae Genus Polygala L. Therophytes, native with distribution in the Southern Cone Region of South America.

Polygala australis A.W. Bennett
Characteristics.Annual or biennial herb, with erect or prostrate leafy stems, 5-15 cm tall.Leaves simple, linear in shape, ca 6-8 cm long and 1-1.7 mm wide.Inflorescence: a spike-like raceme, to 2.5 cm long, with zygomorphic, perfect flowers, ca 2 mm long, with white petals.Fruit: an orbicular capsule that contains seeds with a ring of hairs.
Comments.This is a frequent species in the study area.It grows in shallow, damp soils on grassland slopes and on the summits.Polygala australis shares habitat with P. linoides Poir., which, however, is a perennial herb with lilac flowers (Fig. 24C) and presents seeds without a ring of hairs.Chamaephytes, native with distribution in the Southern Cone Region of South America.
Characteristics.Subshrub with many creeping branches, to 60 cm long, and densely pubescent ascending stems.Leaves with stipulates; ovate to triangular, margins crenate, glaucous, covered with short hairs.Flowers solitary; epicalyx with oval bracts; corolla with pink-lilaceous petals; nerves and basal stained red to violet.Fruit: a schizocarp, with reticulated mericarps.
Comments.This is a frequent species in the study area.It grows in shallow to moderately deep soils on slopes, including grassy slopes, and on summits.In the mountain ranges also grows Pavonia glechomoides A.St. Hil., which differs from P. cymbalaria by the presence of long hair pubescence, suborbiculate leaves, thin epicalyx bracts, and white or pinkish petals with the basal stain purple.Cryptophytes, native with distribution in the Southern Cone Region of South America.
Comments.This is a frequent species in the study area.It grows in shallow soils and in rock cracks on summits and in bare and grassy slopes.In mountain ranges it grows as a small shrub, to 20 cm tall.It is the only species of Psidium occurring in Buenos Aires province.It is recognized from other species of Mirtaceae by its creeping form and the number of sepals.Cryptophytes, native with wide distribution in the American continent.
Characteristics.Perennial herb with pivoting and fleshy roots.Bulb globose, covered with scales from the leaf sheaths.Leaves long, petiolated, trifoliate, pubescent and arranged in a basal rosette.Leaflets semi-fleshy, obovate shape and with subtle emarginated apex.Inflorescence: an umbel, with 3-5 actinomorphic flowers with five pink to purple petals and five sepals.Fruit: a cylindrical capsule.
Comments.This is a very frequent species in the study area.It grows in grassy slopes, cracks, and rocky outcrops on the slopes and on the summit.It differs from other Oxalis that have also been found in mountain ranges, by its simple bulb, leaflet with subtle emarginated apex and inflorescence with at least 3 pinkish flowers.Phanerophytes; native with wide distribution in the Southern Cone Region of South America.Least Concern (Delucchi 2006).
Comments.This is a very frequent species in the study area.It grows in intermediate and full sunlight conditions on grasslands and on slopes in moderately deep, moist soils.It also grows under the trees and in cracks of the slopes and summit.This species could be confused with other Rhamnaceae that are frequently found in the mountain ranges of Buenos Aires province: Colletia spinosissima J. F. Gmel.and Discaria americana Gillies & Hook.These species differ from C. paradoxa in vegetative morphologic characters.Colletia spinosissima has dark yellowish-green branches and cylindrical spines (Fig. 28D), while D. americana has leaf nodes with a transversal mark (Tortosa 1995).Superorder Caryophyllanae Order Caryophyllales: Family Cactaceae: Tribe Trichocereeae Genus Gymnocalycium Pfeiff.Chamaephytes; native with wide distribution in the Southern Cone Region of South America.Vulnerable, reasons unknown (Delucchi 2006).
Comments.This is a frequent species in the study area.It grows in full sunlight conditions in cracks on the slopes.It differs from other Cactaceae from the study area by the color of the flowers; Wigginsia and Parodia species have yellow flowers, while G. gibbosum has white flowers.
Hemicryptophytes, native with wide distribution in the Southern Cone Region of South America.
Characteristics.Perennial herbs with rhizomes and erect branches, to 2 m tall.Leaves glabrous, membranous; basal leaves flaccid, linear, with parallel veins and appressed, solitary bristles in the margin (frequently 2 at the base), to 1 m long and 15 mm wide, larger than the caulinar leaves.Inflorescence: a dichotomous cyme, with ovoid, greenish-white capitulums (1.2 × 1 cm).Fruit: a schizocarp composed of 2 mericarps with lateral scales and vesicles on the upper lower surface, rare or absent in the base.
Comments.This is a frequent species in the study area.It grows in full sunlight conditions, in moderately deep, damp soils and in cracks on the slopes.Up to 2007, E. regnellii was confused with E. stenophyllum Urb.Phanerophytes; endemic to mountain ranges of Buenos Aires province.Critically Endangered, reasons unknown (Delucchi 2006).
Comments.This is a very frequent species in the study area.It grows in various habitats, from deep soils of grasslands, to shallow soils and cracks of the slopes and summit.It is similar to Baccharis draunculifolia ssp.dracunculifolia, but it has linear leaves (length-width ratio 6:3:1-11:6:1), and it does not occur in south-eastern Buenos Aires province.
Characteristics.Shrub with many branches, to 40 cm tall, with pinnatisect, spiniform and rigid leaves, 1-2.5 cm long.Capitulum radiate, bell-shaped, 7 mm long, with white ray outer florets and yellow tubular disc florets.Achenes with glandular and pubescent surface, 3.5-4 mm long, crowned by a white pappus.
Comments.This is an infrequent species in the study area, but it is a common species in other mountain ranges of the Tandilia system.It grows in full sunlight conditions, in the shallow soils and cracks at the summit.Sommerfeltia spinulosa is the only species of its genus that has been found in Argentina.
Characteristics.Suffrutescent with many branches and leaves, 20-60 cm tall.Leaves pubescent, linear, to 2.5 cm long and 2 mm in diameter and with obtuse apex.Capitulums: isomorph, with a brief peduncle and pinkish tubular florets, disposed in dense corymbs.Achenes: cylindrical, with glabrous surface and reddish pappus.
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions, in shallow soils and deep cracks of rocks on the grassland slopes and on the summit.This species is similar to S. multiaristata Spreng and S. aristata Don but S. multiaristata presents long peduncles and S. aristata has rhombic leaves.
Characteristics.Perennial herb, to 60 cm tall, with simple ascending branches, densely covered with leaves and lanate and glandular hairs.Leaves with spatulate shape, mucronate or obtuse apex, entire margin and attenuate to decurrent base.Leaf surface concolor or weakly bicolor with lanate and glandular hairs, denser on the abaxial surface.Inflorescences: capitulums with numerous filiform outer florets and only 3 or 4 tubular disc florets, arrange in glomerules, placed over pseudospiciform arrays interrupted by leaves.Phyllaries with lanate hairs.
Comments.This is a frequent species in the study area.It grows in intermediate and full sunlight conditions and on shallow soils and cracks on the slopes and summit.It differs from other Gamochaeta species that grow in Buenos Aires province by the leaf hair type: G. pensylvanica has lanate and glandular hairs.Cabrera (1963) and Hurrell (2013), who only noted the presence of glandular hairs in G. platensis, considered G. pensylvanica and G. platensis to be different species..However, Freire and Iharlegui (2014) considered that these taxa to be synonyms.
Order Asterales: Family Asteraceae: Tribe Inuleae Genus Pterocaulon Elliott  Hemicryptophytes, native with wide distribution in the Southern Cone Region of South America, previously recorded in Buenos Aires province but not in mountainous areas.
Characteristics.Perennial herb with brief xylopodium, to 80 cm tall, branches tomentouse to glabrous.Leaves with ovate to lanceolate shape, acute apex, dentate edge and decurrent base, giving the appearance of having winged stems.Abaxial surface of the leaves tomentouse; adaxial surface glabrous.Inflorescence: capitulums with numerous filiform outer florets and only 2 or 3 white tubular disc florets.Achenes with glandular-pubescent surface.
Comments.This is a rare species in the study area.It grows in full sunlight conditions, on deep soils and in cracks of the slopes.It differs from other Pterocaulon species that grow in Buenos Aires province by being less than 100 cm tall, and by having dentage, oblanceolate leaves as well as inflorescence with branched spikes.
Cryptophytes; native with wide distribution in the Southern Cone Region of South America.Vulnerable, reasons unknown (Delucchi 2006).
Characteristics.Perennial herb, with latex, rhizomes and simple or bifurcated erect stems, 10-40 cm tall.Leaves arrange in a basal rosette, with oblanceolate shape, lobate to pinnatisect margin, attenuate base and acute apex.Inflorescence: solitary discoid capitulums with yellow florets.Achenes with a short thick beak, ca 0.5 mm in diameter, crowned by a pappus with 1-series plumose hairs.
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions in shallow soils at the summit.Hypochaeris neopinnatifida and H. pampasica Cabrera differ from the other Hypochaeris species in Buenos Aires province by having achenes with beaks that are shorter than the seminiferous portion, and a 1-series pappus hair disposition.Particularly, H. pampasica has a thinner beak than H. neopinnatifida.
Characteristics.Perennial herb with latex; rhizomes erect; stems ramified and lanose, to 60 cm tall.Leaves in a basal rosette, with lanceolate shape, ca 12 cm long, 3 cm in diameter, caulinar leaves smaller and without rigid or stiff bristles.Inflorescence: discoid capitulums with yellow florets in a cymose-corymb inflorescence.The phyllaries have lanuginose hairs mixed with black, short, soft, glandular hairs.Black-red achenes crowned by a light brown pappus.Comments.This is a rare species in the study area.It grows in full sunlight conditions in cracks at the summit.Hieracium palezieuxii Zahn and H. burkartii Sleumer also occur in the region but H. palezieuxii presents rigid and stiff bristles on the stems and leaves, while H. burkartii has rigid bristles on the phyllaries.
Characteristics.Perennial herb with fascicled thick roots.Leaves in a basal rosette, green in the adaxial surface and white in the abaxial one, 0.7-1.5 cm wide, with oblanceolate shape, retrorsely-dentate margin, acute apex and long attenuate base ending in a sheathed petiole.Inflorescence: solitary discoid capitulums at the end of a lanate peduncle, with glabrous phyllaries and three kinds of white florets; ray outer florets (female flowers), filiform intermediate florets (female flowers) and bilabiate disc florets in the center of the head (hermaphrodite flowers).Achenes with a beak and crowned by a reddish pappus.
Comments.This is an infrequent species in the study area.It grows in shallow to moderately deep, damp soils of the summit and grassland slopes.Chaptalia exscapa (Pers.)Baker is a species frequently found in the Tandilia mountain range, but it differs from C. piloselloides by the 2 to 4 cm wide leaves, achenes without beak, and lack of scape when flowering.
Characteristics.Perennial herb with erect stems, to 1 m tall.Leaves with lanceolate shape, acute apex, attenuate base and serrate margin.Adaxial leaf surface lanose to glabrous; abaxial leaf surface tomentose, white.Inflorescence: radiate capitulums with ray yellow outer florets,  and yellow tubular disc florets disposed in cymose-corymb inflorescences at the end of the branches; phyllaries densely covered with white tomentose hairs.Fruits: achenes with sericeous pubescent surface and white pappus.
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions in cracks on the summit.Senecio grisebachii var.subincanus is the only variety of S. grisebachii that has been recorded in the region.It can be recognized by its tomentose, not glandular hairs and its pubescent achenes.Chamaephytes; native with wide distribution in the Southern Cone Region of South America.Least Concern (Delucchi 2006).

Senecio selloi (Spreng.) DC
Characteristics.Suffrutescent, to 1 m tall, with numerous leaves in the base of the plant.Leaves oblanceolate-spatulate, with obtuse apex and serrated margins, densely covered with white glandular hairs.Superior plant leaves sessile, with auriculate base.Inferior leaves with an auriculated pseudo-stalk and attenuate base.Inflorescence: bell-shaped radiate capitulums with yellow ray outer florets and yellow tubular disc florets disposed in loose corymbs.Fruits: cylindrical achenes with glabrous surface and white pappus.
Comments.This is a frequent species in the study area.It grows in full sunlight conditions in deep to moderately deep soils or in deep cracks on grassland slopes.It can be recognized by its densely glandular hairs, entire or dentate leaf margin and 14-15 mm tall involucre.
Comments.This is a frequent species in the study area.It grows in full sunlight conditions in shallow soils on grassland slopes and at the summit.Glandularia tenera and G. peruviana (L.) Small, both commonly in southern Buenos Aires province.G. peruviana has leaves entire and the corolla red.
Order Ericales: Family Primulaceae: Tribe Lysimachieae Genus Pelletiera A. St. Hil.Therophytes, native with distribution in the Southern Cone Region of South Americ; previously recorded in Buenos Aires province but not in mountain range areas.
Comments.This is an infrequent species in the study area.It grows in full sunlight conditions in shallow soils on grassland slopes and at the summit.Pelletiera verna is the only species of its genus in Argentina.Hemicryptophytes, native with wide distribution in the Southern Cone Region of South America; previously recorded in Buenos Aires province but not in mountain range areas.
Characteristics.Perennial, rhizomatous herb with tetragonal stems.Leaves glabrous, with ovate-oblong shape, acute apex and attenuate base.Flowers: terminal or subtermianl, in groups of 1-3 flowers per peduncle; corolla and anthers white.Fruit: 2 mericarps with pubescence at the top.
Comments.This is a very frequent species in the study area.It grows in full sunlight conditions with other short species in deep and moderately deep soils on grassland slopes and at the summit.This species has been described as an annual species (Flora Argentina 2017) contrary to the specimens seen in the Paititi Reserve, which are hemicryptophyte herbs as previously described by Cabrera (1965b) and Delprete et al. (2005).
Order Gentianales: Family Rubiaceae: Tribe Rubieae Genus Galium L. Therophytes, native with distribution in the Southern Cone Region of South America.
Comments.This is a frequent species in the study area.It grows in shaded, moist soils and under the trees.It grows with other Galium species such as G. aparine, an annual herb with sticky hairs on leaves and fruits, and G. hipocarpium, a perennial herb with long peduncle flowers and red berries.Hemicryptophytes, native with wide distribution in the Southern Cone Region of South Americ; previously recorded in Buenos Aires province but not from mountain range areas.Vulnerable (Delucchi 2006).
Comments.This is an infrequent species in the study area.It grows in damp soils, under trees and in grasslands near the summit.It is similar to G. noxium (A.St. Hil.) Dempster ssp.valantioides (Cham.& Schltdl.)Dempster, which, however, has white berries.
Comments: This is a rare species in the study area.It grows in full sunlight conditions in cracks on the summit.Plantago bismarckii Nederlein, a species endemic to the Ventania mountain range, has sericeous-tomentose leaves and a smaller spike than P. tandilensis.

Discussion
Ferns are moderately represented in the Sierra Chica; the study area had 50% of the species that Alonso et al. (2009b) reported from the Tandilia system and only 14% of the taxa reported by Capurro (1961) from the whole of Buenos Aires province.Gymnosperms were represented only by 2 adventive Pinus spp., originating from past plantations.The major taxonomic group was the angiosperms, which are mainly represented by eudicots.This is similar to what has been observed in the Ventania system (Long and Grassini 1997) and in the mountains of other Argentine provinces (Méndez 2009, Oggero andArana 2012).
Of the 364 species recorded in this study, 71 were not included by Alonso et al. (2009b) in a review of the flora of the Tandilia system.Taking into account these 71 taxa, the floristic richness described by Alonso et al. (2009b) would rise from 578 to 649 taxa.This value is similar to the number of specific and infraspecific taxa described for other mountain ranges of Argentina, such as the Ventania system (N = 652), the eastern area of the Cordón del Plata in Mendoza province (N = 667), and the southern part of the Sierras Pampeanas Orientales in Córdoba province (N = 734) (Long and Grassini 1997, Méndez 2009, Oggero and Arana 2012).
The representativeness of the surveyed botanic families (N = 72) was dissimilar because more than 50% of the total identified taxa was grouped into 6 families.The Asteraceae and the Poaceae accounted for 41% of the inventoried vascular plants.The predominance of these families has also been observed elsewhere in Argentina (Flora Argentina 2017) and specifically in several orographic systems in La Pampa, Córdoba, and Mendoza  provinces (Mazzola et al. 2008, Méndez 2009, Morici et al. 2010, Oggero and Arana 2012, Cantero et al. 2014).In Buenos Aires province, the high species richness of these 2 families was previously recorded in the Ventania system (Frangi andBottino 1995, Long andGrassini 1997), and for other mountain ranges of the Tandilia system (Escaray 2007, Alonso et al. 2009a, 2009b, Álvarez et al. 2012).
Therophytes from the Paititi Reserve represented about a third of all taxa found and were mostly adventive species.Among the perennial species, cryptophytes and hemicryptophytes were the most abundant life forms.In these 2 categories, plants keep their buds beneath or at the soil surface, which provides considerable protection against adverse conditions such as shallow soils, high exposure to solar radiation, seasonal drought, and high summer temperatures, conditions that also increase fire danger (Frangi 1975, Mazzola et al. 2008).
According to Zalba and Villamil (2002), the process of invasion by adventive species is dynamic and some species classified as casual and non-invasive can become aggressive invaders due to increases in the number of propagules, changes in the regime of disturbance, and the introduction of other species that may facilitate their expansion.Accordingly, the presence of several exotic tree and shrub species (e.g., Acacia melanoxylon, Laurus nobilis, Prunus mahaleb, and Rubus ulmifolius) as well as some herbaceous species (e.g., Holcus lanatus, Senecio madagascariensis, Cirsium vulgare, and Carduus spp.) that grow spontaneously in different parts of the reserve, may become invasive and thus contribute to the deterioration of natural areas and the loss of native populations (Isla et al. 2001, Monserrat 2010).
The reserve hosted 60% of the native species reported for the Tandilia system by Alonso et al. (2009b), and at least 4% of the endemisms reported for Argentina by Zuloaga andMorrone (1996, 1999), some of which are unique to the Tandilia system, like Baccharis dracunculifolia ssp.tandilensis, Hieracium tandilense, and Plantago tandilensis; others, like Cypella herbertii subsp.wolffhuegeli, Mimosa rocae, Poa iridifolia, and Vicia setifolia var.bonariensis, are also found in the Ventania system (Crisci et al. 2001).These results reveal the remarkable richness of the native flora of the untouched area of the Paititi Reserve.This flora provides shelter and food for numerous vertebrates and invertebrates (Vega andBellagamba 1990, Cicchino andFarina 2007), and the reserve serves to protect genetic resources and provides many ecosystem services (Echeverria et al. 2015).
Finally, this study demonstrates the importance of preserving the mountain range areas of Buenos Aires province, and particularly of this reserve, especially considering that 8% of the inventoried species are threatened species in Buenos Aires province (Delucchi 2006).The adventive species in the Paititi Reserve must be identified and quantified (i.e., density and distribution) to develop mitigation strategies.Native plant species could be used to recolonize and recover degraded sites on mountain ranges in the area.This ecosystem must be preserved to protect its natural resources, allow the conservation of native species, and maintain its role in providing ecosystem services.

Figure 1 .
Figure 1.Location of Paititi Natural Reserve, Tandilia System of Mountain Range, Buenos Aires Province, Argentina.The area surrounded by a red line corresponds to the Paititi Natural Reserve while the area surrounded with a dotted white line corresponds to "Sierra Chica".Satellite image obtained from Sentinel Playground (Sentinel Playground, 2017).

Figure 2 .
Figure 2. Study area. A. Overview of the Paititi Natural Reserve.B. Grassland area.C. Stream area.D. Mountain range slope area.E. Middle mountain range area.F. Acacias area.G. Mountain range summit area.

Figure 4 .
Figure 4. Frequency of different life forms of vascular plant according to its status in the Paititi Natural Reserve.

Figure 3 .
Figure 3. Location.Each number corresponds to a location where certain species were more frequently found.This figure complements tables 1 and 2. Satellite image obtained from Sentinel Playground (Sentinel Playground, 2017).

Figure 5 .
Figure 5. Adiantum raddianum.A. Plant.B. Detail of the sorus that are located on the edge of the pinnules.

Figure 20 .
Figure 20.Lathyrus hookeri. A. Plant.B. Detail of leaves that have turn black after being dried.C. Specimen with white keel and violet standard and wings.D. Specimen with white petals.

Figure 24 .
Figure 24. A. Detail of Polygala australis flowers.B. Detail of P. australis leaves.C. Detail of P. linoides flowers.Figure 23.Vicia setifolia var.bonariensis.A. Plant.B. Detail of leaf and split tendril (arrow).C. detail of the flowers.

Figure 25 .
Figure 25.Pavonia cymbalaria. A. Flower.B. Stem and leaves.C. Detail of the leaves and stipulates (arrows).D. Detail of the back of the petals.

Figure 30 .
Figure 30.Eryngium regnellii.A. Plant.B. Detail of the presence of solitary bristles in the leaf margin.C. Lateral inflorescences.D. Vesicles on the upper back of the mericarp (arrow).

Figure 33 .
Figure 33.Stevia satureiifolia. A. Plant.B. Detail of the leaves and detail of the capitulums disposition (dense corymbs).C. Detail of the brief peduncles.

Figure 35 .
Figure 35.Pterocaulon cordobense. A. Detail of the inflorescence.B. Detail of the winged stem.C. Detail of the leaves.

Table 2 .
Site identifiers correspond to labels in Figure3.The spatial references are geographic coordinates relative to the WGS84 datum.