Vascular Flora of the Tocantins River Middle Basin , Brazil

The data from mapping the vegetation cover of the Brazilian biomes (MMA 2008a) reported at least 38.98% of human disturbed areas and 60.42% of unaltered native vegetation remnants in the Cerrado biome, mostly in the north-northeastern province (Ratter et al. 2003, Bridgewater et al. 2004), whereas the other provinces, such as the central-western, showed the highest rates of deforestation. The aim of this study was to record the vascular flora of the Tocantins river middle basin in order to extend the information on the local vegetation of this region and on the Cerrado flora overall. Introduction The Cerrado biome covers about two million square kilometers or 21% of the Brazilian territory, located between the 5° to 20° S and 45° to 60° W (Ribeiro and Walter 2008). Most of this biome is located in the Central Plateau and its vegetation consists of a mosaic with herbaceous, savanna and forest formations. These formations are limited by climate, physical and chemical properties of soils, fire, water table depth and also human activities such as cattle-raising and deforestation for agriculture (Eiten 1972, Ribeiro and Walter 2008). Among the vegetation phytophysiognomies of the Cerrado biome the cerrado stricto sensu is the dominant type and occurs mostly on Latosols in the highlands, as well as on rocky and lateritic soils. The composition and structure of flora on this latter kind of soil is still dealt with in few studies. Floristic differences are expected in these shallow soils regarding the selective forces acting on vegetation development in these habitats (Felfili and Fagg 2007). The Tocantins river basin, in northern Goiás and southern Tocantins, comprises a few remnants of unaltered native vegetation (MMA 2008a) with floristic types related to the Latosols, Cambisols, Lithosols and Argisols, besides some lateritic soils (SEPLAN 2008, SIEG 2010). This region is located in the mid-western Cerrado province, as detailed in the biogeographic studies of Ratter et al. (2003) and Bridgewater et al. (2004). It consists of a higher abundance of typical species, mostly on mesotrophic soils. Furthermore, there are some vegetation communities associated with the sandy and rocky soils in the highlands of Veadeiros Plateau at altitudes ranging from 700 to 1,600 m (SIEG 2010). Abstract: This study provides a checklist of the phanerogams and pteridophytes of the Tocantins river middle basin, in northern Goiás state and southern Tocantins state, Brazil. Herbarium samples were collected from 2000 to 2009 and this floristic survey recorded 1572 species from 135 families. The most species-rich families were Fabaceae (217), Poaceae (116), Asteraceae (88), Euphorbiaceae (65), Orchidaceae (58) and Malpighiaceae (56). Furthermore, 14 endangered species and 31 rare species were recorded, mainly associated with the campos rupestres in the Veadeiros Plateau region. The flora mainly from the phytophyisiognomies cerrado stricto sensu, campo rupestre (“rocky fields”), mata de galeria (“gallery forest”), mata ciliar (“riverine forest”) and semi-deciduous seasonal forest comprised typical species of the midwestern Cerrado floristic province, such as the most widely known woody plants Anadenanthera colubrina (Vell.) Brenan (popular name angico), Aspidosperma subincanum Mart. ex A. DC. (guatambú), Astronium fraxinifolium Schott ex Spreng. (gonçalo-alves), Callisthene fasciculata Mart. (pau-jacaré), Dipteryx alata Vogel (barú), Guazuma ulmifolia Lam. (mutamba) and Magonia pubescens A. St.-Hil. (tingui). This study is the first to record a wide floristic list of this important region of central Brazil. 1 Embrapa Recursos Genéticos e Biotecnologia, Herbário. Av. W5 Norte (final), Parque Estação Biológica, s/no. CEP 70770-917. Brasília, DF, Brazil. 2 Instituto Chico Mendes de Conservação da Biodiversidade. Centro Nacional de Pesquisas e Conservação da Biodiversidade do Cerrado e Caatinga. EQSW 103/104, Bloco C. Sudoeste. CEP 70670-350. Brasília, DF, Brazil. * Corresponding author: Email: medeiros@cenargen.embrapa.br Marcelo Brilhante de Medeiros 1*, Bruno Machado Teles Walter 1, Glocimar Pereira da Silva 1, Beatriz Machado Gomes 1, Isabela Lustz Portela Lima 1, Suelma Ribeiro Silva 2, Pamela Moser 1, Washington Luís Oliveira 1 and Taciana Barbosa Cavalcanti 1 Vascular Flora of the Tocantins River Middle Basin, Brazil


Introduction
The Cerrado biome covers about two million square kilometers or 21% of the Brazilian territory, located between the 5° to 20° S and 45° to 60° W (Ribeiro and Walter 2008).Most of this biome is located in the Central Plateau and its vegetation consists of a mosaic with herbaceous, savanna and forest formations.These formations are limited by climate, physical and chemical properties of soils, fire, water table depth and also human activities such as cattle-raising and deforestation for agriculture (Eiten 1972, Ribeiro andWalter 2008).
Among the vegetation phytophysiognomies of the Cerrado biome the cerrado stricto sensu is the dominant type and occurs mostly on Latosols in the highlands, as well as on rocky and lateritic soils.The composition and structure of flora on this latter kind of soil is still dealt with in few studies.Floristic differences are expected in these shallow soils regarding the selective forces acting on vegetation development in these habitats (Felfili and Fagg 2007).
The Tocantins river basin, in northern Goiás and southern Tocantins, comprises a few remnants of unaltered native vegetation (MMA 2008a) with floristic types related to the Latosols, Cambisols, Lithosols and Argisols, besides some lateritic soils (SEPLAN 2008, SIEG 2010).This region is located in the mid-western Cerrado province, as detailed in the biogeographic studies of Ratter et al. (2003) and Bridgewater et al. (2004).It consists of a higher abundance of typical species, mostly on mesotrophic soils.Furthermore, there are some vegetation communities associated with the sandy and rocky soils in the highlands of Veadeiros Plateau at altitudes ranging from 700 to 1,600 m (SIEG 2010).

Study Site
The study site included the municipalities of Minaçu and Cavalcante, located in the state of Goiás, and Palmeirópolis, Paranã and São Salvador, in the state of Tocantins (Figure 1).
The climate is the Aw type, in accordance with Köppen classification, which means tropical humid with dry winters and wet summers.The annual rainfall is from 1,400 to 1,600 mm and the average annual temperature is between 23 and 25°C (Silva et al. 2008).
The region is located in the Cerrado biome with remnants of forests, savannas and herbaceous formations.The forest vegetation comprises (sensu Ribeiro and Walter 2008) the seasonal or dry forests, cerradão ("xeromorphic forest"), matas ciliares ("riverine forests") and matas de galeria ("gallery forests") (Figure 2), with the latter two physiognomies located on the banks of the Tocantins river and around seasonal or permanent streams and natural drainage routes.The savanna vegetation, the most widespread in area, includes the cerrado stricto sensu as the dominant type (Figure 3) and small veredas.The herbaceous vegetation is characterized by the campos rupestres ("rocky fields"), campos sujos ("dense fields") and campos limpos ("open fields").

Data Collection
The floristic survey used randomly the 'walk-through' method (Filgueiras et al. 1994).The study was carried out on about 30 expeditions from 2000 to 2009, related to projects of rescue of plant germplasm of Embrapa Recursos Genéticos e Biotecnologia (Cenargen) that aimed to characterize the local flora.All vascular specimens observed in reproductive phase were collected, pressed, dried and subsequently incorporated into the Embrapa Recursos Genéticos e Biotecnologia herbarium (CEN Herbarium), in accordance with the usual methodology (Mori et al. 1985).
The identification of species took place at the herbariums CEN, UB (University of Brasília Herbarium), HEPH (Botanic Garden of Brasília Herbarium) and IBGE (Brazilian Institute of Geography and Statistics Herbarium), using literature and identification by family specialists.The floristic survey follows the Angiosperm Phylogeny Group III (APG III 2009) for flowering plants and Chase and Reveal (2009) for ferns.The names of flowering plants and ferns follow the criteria adopted by Forzza et al. (2010Forzza et al. ( , 2012)).

Results and Discussion
A total of 1572 species from 135 families were recorded (Table 1) indicating a rich flora.The most species-rich families were Fabaceae (217), Poaceae (116), Asteraceae (88), Euphorbiaceae (65), Orchidaceae (58) and Malpighiaceae (56).These families are highly representative in the Cerrado biome (Mendonça et al. 2008, Forzza et al. 2010).Another 55 families reported only one or two species.The richness observed was related to a wide range of collections within different habitats and their vegetation communities, which characterize an element of the regional diversity.After studying the woody vegetation of the Cerrado biome, Ratter et al. (2003) recorded alfa diversity values of up to 100 species in an analysis of 376 different study sites.These authors pointed out that the Tocantins river basin is one of the hotspots for woody diversity in the Cerrado lato sensu.Among the 951 woody species recorded in 376 sites by Ratter et al. (2003) and Bridgewater et al. (2004), more than half were located in only one Cerrado province, with few species widespread in all other provinces.
As regards threatened species, there are 14 that are included on the Brazilian lists (IUCN 2010, MMA 2008b (Giulietti et al. 2009) stood out, with 10 rare species, of which seven were recorded at altitudes of up to 700 m in the region of Chapada dos Veadeiros (Cavalcanti and Noronha 2009).This region is characterized by a number of local endemics, mostly associated with the campos rupestres, where three species of the genus Polygala and two species of Mimosa, as well as H. imbricatiformis, I. connata, S. lanceolata and W. souzae, were also found (Giulietti et al. 2009).
This study extends knowledge on the flora of the Tocantins river middle basin, comprising the phytophysiognomies of cerrado lato sensu, campos rupestres, matas de galeria (gallery forests), matas ciliares (riverine forests) and seasonal semi-deciduous forests.The study area is characterized by species typical of mesotrophic and lateritic soils, besides typical species of the Cerrado and campos rupestres on more dystrophic soils, such as sandy and litholic in the highlands.Additional surveys may increase the floristic data showed in this study of a region that presents high species-richness and several rare species.This study is the first to record a wide floristic list of this important region of central Brazil.

Figure 1 .
Figure 1.Study area and sample sites in the municipalities of the states of Goiás (GO) and Tocantins (TO), Brazil.

Figure 3 .
Figure 3. Cerrado stricto sensu in Tocantins river middle basin located in the municipality of São Salvador do Tocantins (TO), Brazil.