Floristic survey of herbaceous and subshrubby aquatic and palustrine angiosperms of Viruá National Park, Roraima, Brazil

Abstract We provide and discuss a floristic survey of herbaceous and subshrubby aquatic and palustrine angiosperms of Viruá National Park (VNP). The VNP is located in the northern Amazon basin and displays phytophysiognomies distributed in a mosaic where these plants occur, as flooded forests, hydromorphic white-sand savannas, “buritizais” and waterbodies. After expeditions between February/2010 and January/2015 and the analysis of specimens from regional herbaria, we list 207 species of herbaceous and subshrubby aquatic and palustrine angiosperms for the VNP, distributed in 85 genera in 37 families. We recorded six new occurrences for Brazil, two for the northern Brazilian region and 21 for Roraima state. These new occurrences, added to the other species listed here, highlight the floristic similarity between the study site and the Guiana Shield, an adjacent phytogeographical unit and geologically related to the origin of white-sand savannas.


Introduction
Aquatic and palustrine (A&P) plants are able to survive in permanent or periodic submersion of at least their root system and share a few of the adaptations to these habitats (Sculthorpe 1967, Philbrick and Les 1996, Amaral et al. 2008. Th ese plants form an artifi cial group that includes bryophytes, ferns and angiosperms (Sculthorpe 1967, Chambers et al. 2008) and contains species with pronounced phenotypic plasticity (Sculthorpe 1967) which hinder their identifi cation. Th e use of several bibliographic resources and the detailed examination of specimens are indispensable for a reasonably reliable identifi cation. Concurrently, there are a number of diffi culties and peculiarities related to the collecting and preservation process (Fidalgo and Bononi 1989) such as the need of boats, recipients and special papers to press the plants correctly.
Aquatic and palustrine species are important for the structure and maintenance of the habitats where they occur. Th ese plants determine the environmental heterogeneity and water quality of natural and artifi cial waterbodies (Junk 1986, Cronk andFenessy 2001). Studies on A&P plants in the Neotropics focus mainly on ecological analyses, while fl oristic and taxonomic analyses are sparse (Padial et al. 2008, Piedade et al. 2010. Th e Amazon region contains complex river systems with diff erent physicochemical characteristics resulting in two contrasting types of inundated forests, one known as várzea -along white-waters rivers rich in nutrients and suspended sediment -and the other as igapó -along rivers poor in nutrients and, generally, poor in suspended sediments with dark or clear waters (Pires and Prance 1985). Th ese distinctions arise from the origin and drainage areas of rainwater and directly infl uence the diversity of plants, particularly A&P ones. According to Piedade et al. (2010), studies focusing on the richness and ecology of wetland plants are more common in areas of várzea and inventories are still needed in igapó areas.
Th e Viruá National Park (VNP) is among the few protected areas that preserves ecosystems favorable to wetland communities. It receives water discharges from diff er-ent rivers, of diff erent sizes and mostly with igapó characteristics (Junk et al. 2011). Th e distribution of the vegetation in the VNP shows a mosaic-like organization with large areas where the soil is permanently or periodically submersed or saturated with water (mainly white-sand savannas, locally known as "campinaranas") (ICMBio 2014). Th e white-sand savannas can vary from a forested to herbaceous physiognomy (Veloso et al. 1991); this gradual change may be associated with the increasing waterlogging of the soils (Mendonça 2011). Th e herbaceous physiognomy of white-sand savannas covers about 25% of the VNP (ICMBio 2014).
Reports of some preliminary studies in the VNP mention a high fl oristic richness (Gribel et al., unpublished data) but unfortunately, if there are vouchers from these expeditions, none are in any herbaria known to us. Additionally, Gribel et al. (unpublished data) rarely identifi ed herbs and subshrubs at species level, and often listed wetland plants by popular names or only at family or genus level. In fact, these authors never published formal checklists or indicated the material identifi ed during their inventories.
Keeping in mind the existence of vast areas of periodically or permanently inundated ecosystems in the Viruá National Park and the lack of knowledge relative to wetland plants in the region and in areas infl uenced by igapó rivers, we provide and discuss the fl oristic survey of herbaceous and subshrubby aquatic and palustrine angiosperms found there.

Study area
Th e Viruá National Park (VNP; Figure 1) is located in the Caracaraí district, Roraima state, northern Brazil (1°19'11"N; 61°7'17"W DMS). Th e climate in the region is equatorial with the rainy season intercalated by a more or less short dry season, between October and March (ICMBio 2014). Th is protected area presents igneous volcanic or metamorphic rocks in the hills and sandy soil of fl uvial, aeolian or weathering sedimentary origin in the plains (ICMBio 2014).
Th e VNP contains in its 227,011 ha diff erent plant formations distributed in a mosaic (ICMBio 2014) (Figures 1-2): rainforest -typical forested formation of amazon region; white-sand savannas-sandy and leached, forested to grassy, hydromorphic or non-hydromorphic plain areas; and "buritizais" -fl ooded areas dominated by Mauritia palms. Th e protected area has its western boundary at the Branco River, a line drawn a few kilometers from an abandoned fragment of the BR-174 road (known as "Estrada Perdida") as the northern and the eastern boundaries, and by the Anauá River in the southern limit. In addition to the water discharges received from rivers mentioned above, it also receives water from the Barauana River, situated to the east and beyond the limits of the VNP, from the Iruá River, in a south-north axis, and a dense network of streams within its boundaries (ICMBio 2014).

Collecting and analyzing data
We investigate the herbaceous and subshrubby aquatic and palustrine angiosperms. Th e expeditions to collect fertile botanical samples encompassed the local dry and wet seasons, between February/2010 and January/2015. We followed Fidalgo and Bononi (1989) for both the collecting and the herborization processes and vouchers are deposited mainly at INPA and UEC herbaria. When available, we sent duplicates to UFP and/or UFRR herbaria. Th e acronyms are according to Index Herbariorum (Th iers 2015, continuously updated). Our inventory also included specimens previously collected in the study area and deposited at INPA, MIRR and UFRR herbaria.
We chose the collecting points non-systematically but they tended to be more concentrated in peripheral areas and along "Estrada Perdida", due to their accessibility, and in areas where aquatic and palustrine plants are abundant (white-sand savannas of hydromorphic soils, "buritizais" and waterbodies) (Figure 1). Even though the "Estrada Perdida" is outside of the current protected area, a proposal suggests the enlargement of VNP's borders aiming for the inclusion of areas eastwards up to the margins Figure 2. Viruá National Park: habitats and physiognomies. A-B waterbodies with turbid (A) and translucid (B) water; C-D Areas with saturated soils during rainy season (C) and dry season (D); E-G Forested (E given by K.G. Cangani), arboreal (F) and herbaceous (G) white-sand savannas ("campinaranas"). of the Barauana River, such that the "Estrada Perdida" would be enclosed in the VNP (ICMBio 2014).
Additionally, we studied images of specimens deposited at F, K, MO, NY, P, and other herbaria with online digital images. We took into account the reliability of the identifi cations, with preference to types, historical collections and specimens identifi ed by specialists; when available in the literature, we queried the original descriptions and revisions of genera or entire families. Moreover, we consulted specialists when necessary. Rivadavia et al. (2009) described Drosera amazonica Rivadavia, A. Fleischm. & Vicent. and cited the VNP among the localities of its occurrence, and although we did not collect this species, it appears in our list. Pessoa et al. (2015) and Mota et al. (2015), respectively, held two taxonomic treatments with focus on Orchidaceae and Xyridaceae to this area, and we also included the aquatic and palustrine herbs and subshrubs cited by them in our list. When it was impossible to examine directly any specimen of the species treated, we cited the correspondent treatment.
Information on geographic distribution and authors of the species were based on TROPICOS (last access sept/2012), "Lista de Espécies da Flora do Brasil" (Forzza et al. 2015) and specialized literature for each family.
We classifi ed the species analyzed according to morphoanatomical characters and indicated the functional ecological group that they belong ("life forms"). Th e categories represent a continuum from less to more specialized adaptations to the aquatic environment: palustrine plants (growing in saturated soils); emergent plants; rooted with fl oating leaves; free fl oating; and submersed plants (with life cycle entirely or partially under water) (Cronk andFenessy 2001, Chambers et al. 2008).

Results
Th e INPA herbarium was the only that held older specimens collected in the study area. Our fi nal list includes 207 species of A&P herbs and subshrubs, distributed in 85 Table 1.  All life forms were registered in the VNP (see Table 1), with 20% of the species included in more than one category. Palustrine plants encompass 175 species (approximately 85% of species). Th e most species-rich families are Cyperaceae (41 spp.), Xyridaceae (21 spp.) and Lentibulariaceae (17 spp.), all of them common in waterlogged soils. Th e emergent and submerged categories presented 43 and 23 species, respectively, and eight species rooting in mud and with fl oating leaves; while among the free-fl oating plants solely two species were recorded (Pistia stratiotes L. and cf. Eichhornia crassipes (Mart.) Solms). Taking into account only the submerged plants, Lentibulariaceae was the most species-rich family, with eight species of Utricularia. Each of the other families with plants adapted to submersed conditions had between one and three species. Among the families with emergent plants, Cyperaceae was the most diverse, with 16 species distributed in seven genera.

SPECIES
As regards A&P angiosperms listed here, only 13 species appear to be restricted to white-sand savannas (see Table 1), most of these also recorded for areas in the Guiana Shield. Approximately 56 species occur solely in the northern region of Brazil, and fi ve of them are only found in Roraima state.

Identification of A&P plants occurring at VNP
On the identifi cation of A&P plants occurring at VNP, it required the examination of several references, online collections and specialists. Th is correct identifi cation is important as it allows the accurate list and comparison of subsampled vegetation (white-sand savannas; Vicentini 2004) and Amazon area (Hopkins 2007) with other areas and vegetation.  We still are studying some specimens of VNP, but especially when they belong to large genera, such as Eleocharis R.Br. (Cyperaceae), this process can take considerable time in the gathering of scattered and sometimes hardly accessible references.
We observed a population of cf. Eichhornia crassipes in the VNP but all individuals were sterile. Th e identifi cation of sterile specimens is sometimes imprecise but fl oating islands of Eichhornia crassipes were observed in the Branco River (near the urban area of Caracaraí and out of the VNP) and the sterile population shown the aerenchymatous petiole characteristic of this species (Horn 2004). So we decided to list it as cf. E. crassipes (Table 1).
A peculiar case of complex identifi cation in the VNP is the case of Bacopa egensis (Poepp.) Pennell (currently in Plantaginaceae). Th e identifi cation to genus or even family was diffi cult, as the fl oras and taxonomical works consulted did not include the respective genus or contained errors in the identifi cation keys and/or inaccurate descriptions. Not even the description provided by Souza and Giulietti (2009) encompass the morphological variation exhibited in the specimens of the VNP (K4 C3 A3). Specialists previously classifi ed this species in the genus Hydranthelium Kunth and it does not fi t in most descriptions of Scrophulariaceae s.l. or Plantaginaceae or even Bacopa.

New occurrences and endemisms in white-sand savannas/"campinaranas"
Our data indicated new occurrences to both Roraima state and Brazil. It includes species previously registered for the Guiana Shield, an adjacent phytogeographical unit to the north (Funk et al. 2007).
Additionally  (Funk et al. 2007, Forzza et al. 2015. Th e delay of their register may be caused by the insuffi cient collection eff ort in Amazonia region. Among A&P plants, only a few taxa are unique to a vegetation type and/or present restricted distributions (Sculthorpe 1967), and rare species generally display larger distribution areas than those of rare terrestrial species (Santamaría 2002); although Podostemaceae is an exception worth mentioning as they are commonly endemic to a single basin or even a single waterfall (Cook and Rutishauser 2007). Endemic species may occur in white-sand savannas, the predominant vegetation type in the VNP, and such species are probably spread in the numerous isolated "islands" of this vegetation type within rainforest (Anderson 1981).
Th ere is no species endemic to the VNP and the endemic species of white-sand savannas belonging to the A&P plants that we listed here are not restrict to Brazilian territory and occur in other northern South American countries (such as Venezuela, Guyana and/or Colombia) (Table 1). Additionally, in Brazil the apparent restricted distribution in Roraima state may be in part the result of insuffi cient collections in white-sand savannas. We identifi ed some specimens collected in this phytophysiognomies in Amazonas state and not yet deposited in any herbaria, which belong to such endemic species. In fact, endemic species of white-sand savannas were recently listed in other studies of the Viruá National Park (Cabral 2011, Dávila 2011, Azambuja 2012, Cangani 2012, Pessoa et al. 2015, Mota et al. 2015. Other taxa with a more restricted distribution are families, genera or species with concentrated richness or exclusive occurrence in northern South America, or only in the Guiana Shield, e.g. Rapateaceae, Abolboda Bonpl. and Utricularia benjaminiana Oliv.

Life forms
We registered in the VNP all life forms usually recognized to these plants (Cronk andFenessy 2001, Chambers et al. 2008), namely: palustrine (e.g. Xyridaceae), emergent (e.g. Montrichardia arborescens), with fl oating leaves (e.g. Nymphaeae spp.), free fl oating (e.g. Pistia stratioides) and submerged (e.g. Mayaca spp.). It is known that the number of species decreases towards strictly submerged plants ( Barrett et al. 1993), as observed in our data. Gribel et al. (unpublished data) reported the occurrence of species belonging to two genera of free fl oating plants in the "buritizais" in the study area (Wolffi a Horkel ex Schleid. and Spirodela Schleid.), but we did not fi nd specimens of these genera during our expeditions or in herbaria we consulted. Free-fl oating species depend on the nutrients dissolved in the water column (Cronk and Fenessy 2001) and the low richness at VNP may be due to the igapó characteristics attributed to the local waterbodies (low inorganic nutrient concentrations) (ICMBio 2014, Junk et al. 2011.
Th ere are relatively few fl oristic lists for wetland plants in the Amazon region (Piedade et al. 2010) and in particular the northern Brazilian region remains strongly undercollected (Hopkins 2007, Schulman et al. 2007, Piedade et al. 2010. Th is situation makes it diffi cult or even impossible for us to compare our results with other works and probably turns artifacts caused by low sampling into apparent patterns (Hopkins 2007, Piedade et al. 2010. Another study focusing on A&P plants also carried out in the VNP is yet unpublished (Paiva 2012). In it, the collecting eff ort was concentrated in the PPBio (Biodiversity Research Program) grid, in a more forested area within the national park, and in an area of hydromorphic open white-sand savanna near the "Estrada Perdida" road. Th e authors listed 19 species, some of them present in our list. Th e material was identifi ed only in part and at genus level and at the time of our visit to the herbaria in Roraima, the vouchers of Paiva (2012) were not available yet. Since we could not analyze those specimens, the diff erent taxa there listed do not appear in our list, so further comparisons could not be made.
Th e similarity of the aquatic and palustrine fl ora of the Viruá National Park with that of the Guiana Shield is evident, only 17 species of our list are absent in Funk et al. (2007) list. One must consider the geographic proximity between the two areas. Additionally, both have common limiting conditions for many plant species, mainly the nutrient-poor soils (Janzen 1974, Prance and Schubart 1978, Anderson 1981, Steyermark et al. 1995, Funk et al. 2007). Junk et al. (2011) classifi ed the rivers of the study area, including the sediment-rich Branco River, as black-or clear-water due to the low levels of dissolved nutrients. Th e igapó and várzea diff er regarding their fl oristic composition and as to their ecological patterns (Prance 1979, Klinge 1983, Pires and Prance 1985, Piedade et al. 2010, Junk et al. 2011. Prance (1979)  Two species reported in our list, namely Bacopa egensis (otherwise collected in the Solimões River, in Central America -including in rice-fi elds -and even in swamps near New Orleans, Louisiana; Christenhusz 2014) and Glinus radiatus (Ruiz & Pav.) Rohr. (sometimes recorded as weed) are supposedly associated with nutrient-rich habitats. Th ese species were only collected in a lake less than 1 km from the margin of the Branco River (Ano Bom lake, which receives fl oodwater from the Branco River periodically), in an area with gray clay soil. Junk et al. (2011) state that the water of the Branco River, which resembles a white-water river, has low nutrient status and it is thus chemically closer to a clear-water river. Th e presence of these two species suggests that the Branco River may be richer in nutrients than a clear-water river.
Th e comparison of our list with that of an area of várzea near Manaus (Junk and Piedade 1993) illustrates some of these diff erences between nonarboreal Várzea and Igapó areas; only a few species are common to both areas and in the várzea vegetation Poaceae and Araceae s.l. (predominantly Lemnoideae) are the richest families of wetland species. Another study of wetland plants at the Amazonas/Solimões River interface also revealed a low number of species in common with the VNP (Conserva et al. 2008). However, both lists (Junk andPiedade 1993, Conserva et al. 2008) are based on expeditions made during the terrestrial phase (dry season), to facilitate access to the localities, infl uencing the results. Th us, there is an increasing richness of weedy species not necessarily adapted to wetland conditions in both inventories.
Few studies have been carried out in areas of igapó that focus on the diversity of herbaceous and subshrubby aquatic and palustrine plants (Piedade et al. 2010). Lopes et al. (2014) present a fl oristic analysis of A&P plant genera in six river systems with igapó characteristics in the Amazonas state. Th ey listed 25 families and 63 genera, from which 15 families and 24 genera occur in the Viruá National Park (Lopes et al. 2014). Similarly to the pattern observed by Lopes et al. (2014), Cyperaceae is richer than Poaceae in the VNP. Th ose authors did not provide a species list and comparisons are not possible.
Indirectly, Piedade et al. (2010) mention four species to igapó areas: Oryza perennis Moench, Nymphaea rudgeana G. Mey., Utricularia foliosa L. and Cabomba aquatica Aubl. As regards the yellow-fl owered Cabomba Aubl. with four tepals that occurs in the VNP and in the Jufari River (see Piedade et al. 2010), we identifi ed this species as Cabomba schwartzii Rataj. Currently, specialists list this species as a synonym of C. aquatica, typically with six tepals (Forzza 2015). Th e name Oryza perennis is doubtful and specialists will soon submit a proposal to reject it (Robert Soreng, pers. comm.). Th e specimens named O. perennis in Amazonia and the Guianas are probably O. rufi pogon Griff . Th erefore, we also recorded all four species mentioned by Piedade et al. (2010) for the Jufari River in the VNP; all are widely distributed species.
At northern Roraima there is other non-forest vegetation with diff erent abiotic conditions enclosed in the matrix of Amazonian rainforest, the savannas (ICMBio 2014; IBGE 2012). Again, we know little regarding A&P plants in the savannas of Roraima and must take some care when making comparisons with the few works published, such as considering the need for a revision of the identifi cations published in older lists. Th e limitations of useful taxonomic literature, faced especially before the publication of the Flora of the Venezuelan Guayana, were considerable and sometimes researchers vaguely delimited study areas.
Th e fl oristic survey published by Miranda and Absy (1997) gathers data from various previously published inventories and results of the author's collections in the savanna region of Roraima, being the most complete list available to this area. It contains nearly 300 species: c. 30% are from wetlands and of these, 1% in strictly aquatic habitats. We herein recorded 50 of these species for the Viruá National Park, mostly species with a large geographical distribution. More recent lists of aquatic and palustrine species from Roraima state are unpublished (Neves 2007, Paiva 2012, thus only presenting a low number of more widely distributed species. In the updated checklist of macrophytes from northern Brazil, that is based on previous lists plus recent data collected by the authors and data contained in the Spe-ciesLink and "Lista da Flora do Brasil" platforms, Júnior et al. (2015) listed about 540 spp. of A&P plants, among those species only 68 are in common with our list ( Table  1). As their list probably gathers information from Várzea and Igapó areas with no distinction, useful discussions cannot be made at this moment. Anyway, some care must be taken as their list was based on information of the SpeciesLink platform, (according to Moura Júnior et al. 2015), where not all specimens are correctly identifi ed. Th e criterion for the inclusion of the species used by those authors is not clear. Similarly, though the "Lista da Flora do Brasil" is a great source of information about species of the Brazilian fl ora (as cited by Moura Júnior et al. 2015), it is still incomplete and with considerable data gaps for some taxa and geographical regions, such as aquatic and palustrine species and northern Brazil.

Conclusions and future studies
Despite the need for more collecting eff ort in the inner parts of the VNP, its fl ora of aquatic and palustrine herbaceous and subshrubby angiosperms is clearly connected to the fl ora of the Guiana Shield, an adjacent phytogeographical region to the north and geologically related to the origin of white-sand savannas, the predominant physiognomy in the protected area studied here.
Only the INPA herbarium held old specimens from the studied area and although we found some bibliography concerning wetland plants of the region, publications are scattered or the most complete refer mainly the Venezuelan and/or Guiana territory. A greater collecting eff ort and the revision of herbarium specimens are essential to allow for a meaningful evaluation of the similarities and diff erences between the white-sand savannas and other savanna areas of the Amazon. Reasonably complete lists of aquatic and palustrine plants in areas infl uenced by igapó rivers, white-sand savannas and other savannas in the Amazon region may also uncover fl oristic, biogeographical, evolutionary and ecological patterns currently obscured by the inadequate collection status.
To allow for the identifi cation of the species here listed, our group is currently producing keys (including interactive multi-access keys), descriptions with images, taxonomic comments, geographical distribution and fi eld observations of the listed taxa. We will provide these resources shortly, in the format of an eFlora on a website about the Viruá National Park (Costa et al. in prep.). aceae), Gisele Oliveira and Nara Mota (Xyridaceae), Nancy Hensold (Eriocaulaceae), Andrew Henderson (Arecaceae), Kátia Cangani (Melastomataceae), and Ricarda Riina (Euphorbiaceae). We thank Cynthia Sothers, Royal Botanic Gardens, Kew, for correcting the English version of the manuscript.