Additional list of species of aquatic macrophytes in the lower basin of the Xingu

In this paper the authors present an additional list of aquatic macrophytes in the lower basin of the Xingu River.


Introduction
The lower stretch of the Xingu River is characterized by a diversity of habitats, with large uneven rapids, a series of anastomosing channels, oxbow lakes and high amount of tributaries.This heterogeneity generates hydrological and limnological conditions that allow the occurrence of a variety of aquatic macrophytes.
In the article by Medeiros et al. (2015) presented in this special issue, the authors also conducted a survey of the species of aquatic weeds that occur in the same region.However, in this study the authors gave greater emphasis on closely related species to water bodies, since the main objective was to evaluate the species with great potential for infestation and that could cause problems in areas of the reservoirs under construction in the Xingu River.
In the present study, the sampling efforts were directed to a wider area including wetlands, parafluvial zone of the Xingu River, as well as the edges of islands and stretches of the Xingu river rapids.Therefore, it is a complement of the previous survey conducted by Medeiros et al. (2015).

Methods
This survey is part of the monitoring program that is being conducted in the influence areas of the Belo Monte hydroelectric dam.Sampling of aquatic macrophytes was carried out in four campaigns, considering one full hydrological cycle: October of 2014 (dry), January (flood), April (full) and July of 2015 (ebb) (Figure 1).
The species list followed the classification of families proposed by APG III (2009) for angiosperms, by Smith et al. (2006) for pteridophytes, and Buck and Goffinet (2000) for bryophytes.Plant names and respective authors were checked at the data bank of the Botanical Garden o Rio de Janeiro (Reflora, 2015).
A total of 189 species of aquatic macrophytes were observed (Table 1).The most represented families were Fabaceae (27 species), Cyperaceae (26 species), Poaceae (22 species) and Rubiaceae (10 species) (Figure 2).Amphibious forms were dominant (60%), followed by emergent plant species (26%), while free-floating were represented by 3% and rooted-floating by 3%.Considering the plant families, Moura Júnior et al. ( 2015) also found Poaceae, Cyperaceae and Fabaceae as the most representative families in a checklist of aquatic macrophytes carried out for the Northern region of Brazil.These authors also observed an unprecedent richness of Podostemaceae due to their efforts on favorable habitats, a procedure not performed in the present study.Nevertheless, five species of Podostemaceae were observed in stretches of rapids in the Xingu River in the present study, most belonging to the genus Mourera, and the species Mourera fluviatilis appears in the list of endangered species of flora (Brasil, 2008) (Figure 2).

Results
Table 1 shows the additional list of species of macrophytes found in the lower basin of the Xingu River.

Discussion
Although the number of species observed in the present study was higher than that observed by Medeiros et al. (2015), who registered 106 species over two years of monitoring, the proportion of life forms was similar.The high number of amphibian species observed in this study is due to greater efforts directed to the characterization of plants living in the fllodplains and in the parafluvial zone of the Xingu River and tributaries.These results show the importance of these areas as habitats for aquatic macrophytes in the Xingu River basin.

Figure 1 .
Figure 1.Map of the lower basin of the Xingu River showing the sampling stations of aquatic macrophytes in the period between December 2011 and April 2015.

Figure 2 .
Figure 2. Life forms and proportion of families of aquatic macrophytes in the riverine landscapes of the Xingu River.

Table 1 .
List of families, species, life forms and habitats of aquatic macrophytes in riverine landscapes of the middle Xingu River recorded from October 2014 to July 2015.