Using White Star (Nymphoides humboldtiana) for lake landscaping

on the ornamental potential of aquatic herbaceous plants can be found in journals (Stumpf et al., 2015; Devi et al., 2015; Blidar, 2017). This fact limits the knowledge about the cultivation of these species and consequently their supply in the market. The genus Nymphoides presents more than 50 species distributed in the world (Tippery & Les, 2011), in which aquatic and semi aquatic herbaceous plants with well developed aerenchyma predominate (Souza & Lorenzi, 2005). Among these species Nymphoides humboldtiana, Brazilian native species, Studies on ornamental potential of herbaceous plants are many and show potential of different species, such as: Baccharis articulata, B. usteris, Hipericum connatum (Stumpf et al., 2009), Andropogon bicornis, Aspilia montevidensis, Bidens laevis, Brasiliorchis porphyrostele, Bromelia antiacantha, Hybanthus bicolor, Petunia axillaris, Salvia procurrens (Stumpf et al., 2015) and Tropaeolum pentaphyllum (Prestes et al., 2015). However, the same advance is not observed for aquatic herbaceous plants. Over the past ten years, fewer publications about studies F market is an important segment in economy. It consists of a large productive chain and is always in search of innovations. The estimated value for this chain in 2018 was 7.2 billion reais (Junqueira & Peetz, 2018). Evaluating the potential of Brazilian native species enriches our biodiversity, it can also minimize commercial production costs of these plants for its higher adaptability to cultivation environment (Stumpf et al., 2009, 2015), as well as to mitigate the environmental impact caused by the extraction of these plants for ornamental purposes. ABSTRACT

on the ornamental potential of aquatic herbaceous plants can be found in journals (Stumpf et al., 2015;Devi et al., 2015;Blidar, 2017). This fact limits the knowledge about the cultivation of these species and consequently their supply in the market. The genus Nymphoides presents more than 50 species distributed in the world (Tippery & Les, 2011), in which aquatic and semi aquatic herbaceous plants with well developed aerenchyma predominate (Souza & Lorenzi, 2005). Among these species Nymphoides humboldtiana, Brazilian native species, Studies on ornamental potential of herbaceous plants are many and show potential of different species, such as: Baccharis articulata, B. usteris, Hipericum connatum (Stumpf et al., 2009), Andropogon bicornis, Aspilia montevidensis, Bidens laevis, Brasiliorchis porphyrostele, Bromelia antiacantha, Hybanthus bicolor, Petunia axillaris, Salvia procurrens (Stumpf et al., 2015) and Tropaeolum pentaphyllum (Prestes et al., 2015). However, the same advance is not observed for aquatic herbaceous plants. Over the past ten years, fewer publications about studies F lower market is an important segment in economy. It consists of a large productive chain and is always in search of innovations. The estimated value for this chain in 2018 was 7.2 billion reais (Junqueira & Peetz, 2018).
Evaluating the potential of Brazilian native species enriches our biodiversity, it can also minimize commercial production costs of these plants for its higher adaptability to cultivation environment (Stumpf et al., 2009(Stumpf et al., , 2015, as well as to mitigate the environmental impact caused by the extraction of these plants for ornamental purposes.

ABSTRACT
White Star (Nymphoides humboldtiana), an aquatic-environmental native species of Brazilian flora, was selected in order to be used as ornamental plant in lakes. White Star plants were submitted to two water levels (high water level, up to 30 cm water depth and, low water level until substrate saturation) and two light intensities (full sun and 50% shading) to evaluate vegetative and flowering development. The experimental design was completely randomized, in a subplot scheme, being the water level the main plot and luminosity the subplot. Seven replicates were performed, and the sample unit consisted of one plant. Data related to number of leaves and flowers, length and diameter of petioles and leaf area were submitted to analyze of variance and regression. We observed an increase in number of leaves and flowers in the treatment of high water level in full sun, and an increase of petiole length in high water level with shading. No difference between leaf area of plants grown under full sun and with shading (p<0.05) was observed. At low water level, plants presented lower vegetative development than those grown at high water level, besides the flowering inhibition in shaded condition. These results demonstrated that White Star can be used in ornamental lakes with a water depth of at least 20 cm above the rhizome and exposed to full sun.

Received on February 23, 2018; accepted on January 15, 2019
can be found in all biomes (Flora do Brasil, 2017), and is commonly known as White Star.
The plant has two stem structures, a rhizome and a stoloniferous stem, horizontal to the substrate, with petioles that, when not branching on the surface of the water, emit only a floating leaf (Souza & Lorenzi, 2005;Tippery & Les, 2011;Barcelos & Bove, 2017). Petioles can reach up to 300 cm length and are submerged (Pott & Pott, 2000). The leaves attached to the petiole, when in aquatic environment, remain with the abaxial surface in contact with water (Barcelos & Bove, 2017). Flowers emerge at the end of spring from the submerged portion of the petiole, a few centimeters from the water surface and remain open for only one day. Flowers are white-colored pentameras, 2.0 to 2.5 cm in diameter (Pott & Pott, 2000). According to Wang et al. (2005), the process of flower formation is the same as in N. peltata. The differentiation begins on the day before the opening, below the water surface, when cylindrical pedicels, measuring from 4 to 7 cm, with floral buds, are developed. On flowering day, the buds are raised above the water level and flowering occurs.
White Star was selected in this study, based on Composite Index of Ornamental Potential of Tropical Species (Chamas & Matthes, 2000), using the evaluation carried out in the field, according to what was pointed out in Tedesco (2011).
The goal of this study was to evaluate the adaptability of this species to different waterlogging conditions and different luminosities, aiming to use this plant for landscaping.

MATERIAL AND METHODS
The experiment was installed at Pavilhão de Aquáticas da Faculdade de Agronomia e Medicina Veterinária of Universidade de Passo Fundo-RS (28°13'52"S, 51°22'50W) on September 9, 2008. The experimental design was completely randomized, in a split-plot arrangement, with water allocation level in the main plot and luminosity in subplot. Leaves and petioles were evaluated weekly, after 10 days of experiment installation. Flowers were registered every two days after flowering beginning, from September 23, 2008 to April 5, 2009. The experiment was carried out in polyethylene pots (5-liter capacity). The 16-meter-height pots were filled with Rhodic Hapludox substrate (Streck et al., 2008), collected in the experimental area at Universidade de Passo Fundo, in the layer from 0 to 20 cm. We put in each pot one Nymphoides humboldtiana rhizome, previously washed in running water and sanitized using hypochlorite solution (diluted 5%). The rhizome, without leaves, presented at least three internodes, 4 to 6 cm length. The rhizomes were collected in Capiguí dam, in the municipality of Mato Castelhano-RS (28 o 34'68"S, 52 o 22'02"W), on January, 2008. The matrix rhizomes were kept in production in Pavilhão de Aquáticas (Aquatic Pavilion) until the experiment installation.
The species development was studied under two environmental conditions: water level, which is variable in aquatic/terrestrial transition zone and luminosity. In relation to light intensity, the authors tried to simulate the shading due to the presence of margin plants, large trees, pergolas and even wet decks, little permeable to radiation and exposure to full sun.
Two water levels were evaluated, considering that the high level consisted of a permanent maintenance of a water depth from 20 to 30 cm (submerged pots), and the low level in a water saturated substrate (pots filled with water-soaked soil). Water level was controlled using a water faucet, independently for each treatment. Two luminosity conditions were evaluated, full sun and shading (using black shading screen 50% sombrite ® ). Each treatment consisted of seven replicates. The experimental unit consisted of a 5-liter pot containing rhizome, totalizing 28 experimental units.
During the experimental period, we evaluated number of leaves/plant; leaf area of the largest leaf, length (cm) and diameter (mm) of the petiole base and number of flowers. After the weekly evaluation of these traits, pots were rotated, in order to avoid a possible local effect in the experiment. For evaluation, we considered the leaves with 50% or more green area, those in expansion and those totally expanded. For leaf area evaluations, the authors measured length and width of the largest leaf of each pot, since removing the leaves from the plants would affect flowering. Leaf area was calculated indirectly (length multiplied by width/correction factor 1.37). Correction factor was obtained using the average value of twelve leaves in different development stages and different treatments. Correction factor was calculated using division of the real area, obtained by measuring the leaf area, by the calculated area (length x width).
The presence of other plants and fauna was controlled by manual harvesting, when found in pots or in the tank.
Obtained data were submitted to analysis of regression and variance, and then, the Tukey test at 5% probability was used to compare the averages, with the aid of SISVAR software (Ferreira, 2014).

RESULTS AND DISCUSSION
Leaves were emitted in all White Star rhizomes, 14 days after transplant. This aquatic species showed better development, greater number of leaves and flowers, when grown in 30 cm water depth under full sun. Less quantity of leaves was produced only in low water level in shady conditions (Table 1, Figure 1). Luminosity reduction favored an increase of leaf area and petiole length when grown in 30-cm water depth. Probably, as in Nymphoides peltata, the adaption to full sun is more determinant than water depth (Zhonghua et al., 2007).
In this study, the presence of this caterpillar was associated with low luminosity. The caterpillar consumed pieces of leaves or the whole leaf, affecting negatively the leaf area in that period of the experiment.
When plants were grown under 30 cm water depth, the leaves showed more than twice the leaf area of those cultivated under water saturation conditions, and in this case, when submitted to low luminosity, a higher reduction in leaf area was noticed (Figure 1). In N. peltata, the authors noticed physiological adaption to water level variation, which may suggest different behavior for this species (Yu et al., 2014). This biomass accumulation of White Star in a high luminosity environment and high water depth favored floral exuberance, since no flowering or minimum flowering was noticed, when the plant was grown in a shaded place under low water depth. Generally, in aquatic plants, the appropriate combination of temperature and luminosity provides an increase in nutrient uptake capacity (Pott & Pott, 2000;Lacoul & Freedman, 2006;Palma-Silva et al., 2008). Moreover, other factors are determinant in nutrient acquisition, such as the speed of flooding and water column depth (Lacoul & Freedman, 2006;Richards & Cao, 2012). In this case, the authors noticed no difference in the leaf area of plants grown under 30 cm water depth, both in places with high and low luminosity, discarding the idea of differential allocation of photoassimilates.
Petiole diameter showed no significant variation among treatments, but varied from 0.27 to 3.00 mm when leaves started emission, up to the flower emission, respectively. In this study, as also verified in the study with N. peltata (Yu & Yu, 2010), the presence of green petioles was noticed (Figure 2), showing photoassimilate production in these submerged structures.
In aquatic-rooted-floating-leaved plants, both stem and petiole elongation occur in order to stimulate searches for luminosity and gases (James, 2008;Colmer & Voesenek, 2009). No elongation of the petiole was verified in plants grown under low water depth (Table 1), regardless the presence of luminosity. When these plants are grown under high water depth, they presented longer petioles in shaded environment, due to the fact that the plant searches for luminosity. The authors observed that in each pot rotation, the leaves in pots near the border of sombrite showed positive phototaxis.
Petiole elongation, in order to keep floating leaves, is a positive value, considering plants for landscaping, since this trait shows that the aquatic plant can be used both in shallow lakes (20 to 30 cm) built in residences with smaller gardens, and in up-to-300-cm  lakes in natural environments (Pott & Pott, 2000). White Star flourished for a period of 144 days, from mid-spring to early autumn (November, 12 to April, 5). Flowering was favored in plants which were grown in full sun environment under high water depth, reaching up to 2 flowers/day/rizhome. No flowering emission was noticed in shaded environments without water depth (Table 1). At the beginning and the end of this period, low flower production was noticed. Flowering period of N. humboldtiana coincides with the flowering period of N. peltata (Wang et al., 2005) and N. aquatica (Richards et al., 2010), which also flourish seasonally. Water depth determined flowering, followed by luminosity. This result shows plasticity in flowering response in relation to N. humboldtiana plant conduction in shaded environments by other plants, such as moist areas, lakes or gardens. In this study, plants did not flourish in water saturated soil (low water level) under shading. However, in the same condition of water, full sun, no significant difference was observed in number of flowers.
Although showing a delicate appearance (Figure 2), flowering is a positive trait in its use as an ornamental plant, due to its abundance and long period, even though the number of flowers has decreased up to 43% when grown in a shaded place (Table 1), under high water level. White Star showed a 20-week flowering period, exceeding the observed fiveweek period in N. aquatica (Richards et al., 2010).
Using data obtained in this study, the authors recommend the use of N. humboldtiana for landscaping of shallow lakes, provided that the water level exceeds the level of the substrate and under full sun. This species also shows viability to be grown in shaded environments, when the main ornamental interest is to cover the water surface with leaves.

ACKOWLEDGEMENTS
To Dr. Lisete M. Lorini, from Laboratório de Entomologia da U n i v e r s i d a d e d e P a s s o F u n d o (Entomology Laboratory) for the caterpillar identification. To CNPq for productivity scholarship for Edson C. Bortoluzzi.