The genus Chamaecrista Moench in a fragment of the Ecological Station Raso da Catarina , Bahia , Brazil

Chamaecrista has a Pantropical distribution, with some occurrences in Australia and temperate areas, and includes about 330 species, of which 266 occur in the Americas. The genus is represented in Brazil by 256 species, of which 97 are cited for the northeast Region. The Ecological Station Raso da Catarina (ESRC) is one of the largest areas of protected Caatinga and occupies about 105,282.00 ha., delimited by the coordinates 09°39’0.30” to 09°50’98.2” S and 38°26’57.5” to 38°29’32.6” W. The floristic survey of Chamaecrista in the ESRC included analysis of specimens collected from March 2010 and October 2011. The analyses were supplemented with dried collections from the following herbaria: ALCB, EAC, HRB, HUEFS and MBM. The genus is represented in the study area by ten taxa. The most representative taxa in the area were Chamaecrista repens (Vogel) H.S.Irwin & Barneby var. multijuga (Benth.) H.S.Irwin & Barneby, C. brevicalyx (Benth.) H.S.Irwin & Barneby var. brevicalyx, C. belemii (H.S.Irwin & Barneby) H.S.Irwin & Barneby var. belemii, wich are directly related to sandy soils common in the region. The taxonomic treatment includes a key for the identification, descriptions, illustrations, photos, data geographical distribution, reproductive phenology and comments about the taxa.


Introduction
Chamaecrista was established by Moench (1794), segregating it from Cassia s.l.(Irwin & Barneby 1982).It is one of the largest genera of the subfamily Caesalpinioideae and the largest of the subtribe Cassiinae (Lewis 2005).It has a Pantropical distribution, with some occurrences in Australia and temperate areas.The genus includes approximately 330 species, of which 266 occur in the Americas (Irwin & Barneby 1982, Lewis 2005).
In Brazil, the genus is represented by about 256 species, of which 97 are cited for the Northeast Region.Bahia is considered to be the state with the third greatest number of taxa of Chamaecrista with 91 species.The center of their diversity is in campos rupestres (rocky fields) (Lewis 1987, Conceição et al. 2001, Zappi et al. 2003, Souza & Bortoluzzi 2016).In Caatinga twenty-nine species were recorded for Chamaecrista (Queiroz 2009).
Chamaecrista is mainly characterized by presence of two alternate bracteoles on the pedicel of the flowers, convex extrafloral nectaries and spiraled elastically dehiscent fruits.According to Irwin & Barneby (1982), the genus includes six sections.All phylogenetic studies based on morphological and molecular data supported the monophyly of Chamaecrista (Conceição et al. 2009, Rando et al. 2016).However, with regard to infrageneric classification, the study of Conceição et al. (2009) showed that only two of the six sections recognized by Irwin & Barneby (1982) are monophyletic.Rando et al. (2016) supports the monophyly of C. ser.Coriaceae, suggesting C. ser.Flexuosae as the sister group of this clade.
Despite the existence of studies about Chamaecrista for the semiarid of northeastern Brazil, regional works for the state of Bahia are scarce, especially those that include keys of identification and descriptions.Given the importance of Chamaecrista in the Caatinga vegetation, this work had as a goal to carry out the survey of the species of the genus in the Ecological Station Raso da Catarina (ESRC) in order to contribute to knowledge about the flora of the semiarid region of Bahia as well as to support the development of the ESRC management plan.

Material and Methods
The Raso da Catarina Ecoregion comprises 30.800 km 2 and is one of the eight Ecoregions recognized for the Caatinga and includes units of conservation.In the North-south direction it is narrow and elongated.In the North, West and East directions it is limited to the southern hinterland depression.The northeastern portion has limits with the Borborema Plateau and the southern part of the Bahia hinterland, in the Zona da Mata.The Ecoregion is a basin with soils that are very sandy, deep and little fertile.Its relief is very flat, but with canyons in the western part (formed by sandstone outcrops).The altitudes above sea level vary from 400 to 600 m in the southern part (Bahia) and from 350 to 700 m in the northern part (Jatobá basin, Pernambuco).In the southern part (Bahia) most of the soils are composed of sand (deep, excessively drained, acid and very low fertility) and oxisol (deep, well drained, acid and low fertility) whereas in the northern part (Pernambuco) sands soils prevail.There exists little surface water in the region except in the areas of the canyons.The predominant vegetation is the sandy, bushy Caatinga, very dense and less thorny than the Caatinga of crystalline soils (Velloso et al. 2002).
The Ecological Station Raso da Catarina (ESRC, Figure 1) is one of the protected areas of the Raso da Catarina Ecoregion.It is one of the largest areas of protected Caatinga and occupies about 105,282.00 ha., delimited by the coordinates 09°39'0.30" to 09°50'98.2" S and 38°26'57.5" to 38°29'32.6"W, limited to the North with the Pankararé aldeia, to the east with the municipalities of Rodelas and Canudos, to the South with the municipality of Jeremoabo and West with the municipalities of Paulo Afonso and Jeremoabo.The climate of the ESRC is semiarid with average rainfalls of 500 mm/year and annual temperature is approximately 23ºC (Szabo et al. 2007).The soils are generally sandy deep and very fertile relief plan with sandstone formations (Velloso et al. 2002).
The study was based on fieldwork carried out in the period between March 2010 and October 2011, besides information complemented by the analysis of species deposited in the herbaria: ALCB, EAC, HRB, HUEFS and MBM, acronyms according to Thiers 2016 (continuously updated).The field collections and observations were performed during random walks exploring most of the study area.Herborization and material processing followed the methodology by Fosberg & Sachet (1965) and Mori et al. (1989), where fertile material was collected with flowers and/or fruit.Observations were made about the distribution of the species and the type of soil (Tricart 1972, Sampaio 1995).The specimens were deposited in the herbarium of the State University of Bahia (HUNEB -Collection Paulo Afonso) and the duplicates were sent to the main herbaria in the state of Bahia.
The identifications were made based mainly on specialized bibliographies (e.g., Irwin & Barneby 1978, 1982and Queiroz 2009), protologues, photos of type collections and consulting of the collections in the herbaria that were visited.For the taxonomic descriptions, the terminologies proposed by Radford et al. (1974), Irwin & Barneby (1978, 1982), Ribeiro et al. (1999), Harris & Harris (2001) and Gonçalves & Lorenzi (2011) were adopted.The taxonomic treatment includes a key for the identification of taxa, descriptions, illustrations, and data of the geographical distribution and reproductive phenology of the species.
Herbs, shrubs or subshrubs, erect, prostrate, sarmentose, decumbent or procumbent, little or profusely brancheds; branches cylindrical, rare quadrangular, straight, sometimes tortuous, rare fractiflex.Leaves green, alternating, paripinnate, 2-multifoliolate; extrafloral nectaries present or absent, when present with concave secretory surface, sessile and discoid or stipitate and caliciform, located on the petiole, rarely on the rachis and pairs of leaflets.Inflorescence racemose, elongated, or reduced in fascicles axillary or supra-axillary, with few flowers or reduced to a single flower; bracteoles 2, alternating or subopposite, than in different positions on the pedicel; flowers pentamerous, asymmetric; sepals free, the internal larger the ones; petals free, yellow to orange, heteromorphic, with a differentiated internal abaxial petal (cuculus), falcate, spatulate to suborbicular, bent on the stamens, protecting the androecium, stamens 10, homomorphic, arranged at equal length levels or at different levels, anthers dehiscent by apical pore.Legumes elastically dehiscent, oblong, plan-compressed, with valves chartaceous or coriaceous, spiraled after seed release.Seeds compressed, glossy, rhomboid to pyriform, testa dark brown, pitted, pits aligned in vertical rows.

Chamaecrista amiciella
Material examined: BRAZIL, BAHIA: Paulo Afonso, Estação Ecológica Raso da Catarina, Chamaecrista amiciella is endemic to the Caatinga and has been recorded in southern Ceará, western Paraíba and northern Bahia, where it occurs on sandy soil at altitudes between 150-500 m (Irwin & Barneby 1978, Queiroz 2009).In the ESRC the species is rare and occurs on sandy soil at altitudes of 580-660 m.It was collected with flowers and fruits in January, December and June.

Chamaecrista nictitans
Material examined: BRAZIL, BAHIA: Paulo Afonso, Estação Ecológica Raso da Catarina, Trilha sentido Mata da Pororoca, 9°48'32" S and 38°29 '30 W, 584 m, 24.III.2010, fl.;  Chamaecrista nictitans is widely distributed in the Americas, occurring from the United States to Argentina, and includes four subspecies and 11 varieties, of which only disadena and pilosa occur in the Caatinga.In the study area, the species is represented by Chamaecrista nictitans var.disadena (Irwin & Barneby 1982, Queiroz 2009).This taxon is quite common in the ESRC, and is found in more degraded areas on sandy-clayey soil at altitudes of 570 to 696 m.It was collected with flowers and fruits from December to March and June to September.

Chamaecrista ramosa
The species occurs in South America and includes six varieties (Irwin & Barneby 1982).This species is inserted in C. sect.Xerocalyx that possesses taxa with limits that are considered artificial.In 2005 based on morphological data Fernandes & Nunes recognized only four varieties for the species.A biosystematic study of C. sect.Xerocalyx is in progress and should certainly help to more naturally delimit the taxa of this section.In the study area, the species is represented only by the ramosa variety, which is rare.This variety occurs from north South America to east Brazil (Irwin & Barneby 1982, Queiroz 2009).
In the study area, the taxon can be easily recognized by erect procumbent to subshrub habit with leaves having 2 pairs of leaflets with paralelinervous venation and by isolated axillary flowers.The species is endemic to northeastern Brazil, having been recorded to southern Maranhão and Piauí to western Pernambuco and Paraíba (Irwin & Barneby 1982, Queiroz 2009).In the study area, Chamaecrista tenuisepala is very common and occurs on sandy, sandy-clayey and rocky soils at altitudes of 520 to 667 m.It was collected with flowers and fruits nearly every month of the year.
Chamaecrista tenuisepala can be recognized in the area by subshrub habit, lanceolated to deltate stipules, stipitate and caliciform extrafloral nectary located on the petiole below the pair of proximal leaflets, leaves with 5-6 pairs of leaflets and isolated axillary flowers of ca.1.5 cm in diam.

Figure 1 .
Figure 1.Location of the fragment studied in the Raso da Catarina Ecological Station (Varjão et al. 2013, modified).