The Brazilian Cerrado is one of the most threatened ecosystems in Brazil and was ranked among the 34 most important biodiversity hotspots of the world (Mittermeier et al. 2004). In the first survey of the Cerrado flora, Mendonça et al. (1998) listed ca. 6,000 angiosperm species. After that, efforts to raise the knowledge on biodiversity for this area nearly doubled the number of species, with the monocotyledons (Lilianae) accounting for roughly 25% of the increase (Sano et al. 2008). The Araguaia River basin runs through the states of Goiás, Mato Grosso, Tocantins, and Pará; covering 373,000 Km² (Lima et al. 2004), mostly within the Cerrado. The region is rich in wetlands like rivers, streams, temporary or permanent swamps and pools. The climate is characterized by high temperatures that reach 100.4 °F in September and October and strongly seasonal precipitation of 1750 to 2000 mm per year. There are two well- defined seasons: the dry season (July-November) and the rainy season (December-June) (IBGE 1989). This basin is dominated by plinthosoils, which are poorly drained and usually found in low flat areas prone to flooding (Resende et al. 1995), forming temporary or permanent swamps. The importance of wetland habitats ecologically and in terms of plant biodiversity globally has been emphasized by many authors (e.g. Gopal and Junk 2000, Thomaz and Cunha 2010, Paz and Bove 2011, Mendonça et al. 2012, Moura-Júnior et al. 2013). On the other hand their taxonomic diversity is rarely the focus of wetland studies (e.g. Pedralli et al. 997, Bove et al. 2003, Moreira et al. 2011, Contaifer et al. 2013, Sabino et al. 2015).

The first study to include aquatic plants in Brazil was carried out by Hoehne (1915) in the Cerrado and in the Amazon Forest. The same author published “Plantas Aquáticas” (Hoehne 1948), a pioneer study of aquatic flora from Brazil. Also, species from Pantanal have been studied (Pott and Pott 1997, Pott and Pott 2000). A checklist from the states of Mato Grosso and Mato Grosso do Sul (Dubs 1998) and the vascular flora of the Emas National Park, located in the Araguaia River basin (Batalha and Martins 2002) incidentally included some aquatic plants, though they did not survey aquatic ecosystems. In spite of the vast area encompassed by the Araguaia River basin and the broad diversity of wetland habitats, the aquatic and marshy flora of this region is little known. This work contributes to a better understanding of the aquatic environments in the Cerrado and other savanna-like vegetation physiognomies. Notably, herbarium collections are depauperate with respect to aquatic plants, reflecting both the difficulty of collecting in wetlands, as well as the scarcity of specialists in the taxonomic groups included. Generally, these plants are incidentally collected by terrestrial plant specialists and the quality of incidental collections may challenge correct identification. Thus, the real diversity of the aquatic flora from the Brazilian Cerrado will be better known through studies carried out by specialists focusing on aquatic habitats on the region. Our efforts to improve the knowledge of the aquatic flora from the Araguaia River basin have resulted in the discovery of new species (Koehler and Bove 2001, Oliveira et al. 2011) and on the better understanding of taxonomic groups such as the Alismatales (Koehler and Bove 2004) and Cyperaceae (Gil et al. 2007, Oliveira et al. 2011). As a result of an intensive search of collections and field work, we provide here an annotated list of aquatic and marshy monocots found in the Araguaia River basin. The results increase our knowledge of biodiversity in this basin and in the Cerrado. Species not previously reported to this area are highlighted. We also include images of the specific habitats and species from the Araguaia River basin.