The aim of this study was to investigate the seasonal effect of wet and dry periods on the composition and structure of flooding grassland. Thirty quadrats (0,5 m×0,5 m) were used in each period (wet and dry) to estimate the degree of covering of the species. Phytosociological parameters, diversity and similarity indices were calculated between periods. Forty eight species were collected, 35 genera distributed in 20 families. Cyperaceae (10), Poaceae (six) and Euphorbiaceae (five) were the families with the highest number of species. Therophytes were the most abundant (41,02%), followed by hemicryptophytes (23,08%). Diversity and richness were higher in wet season (S = 41, H'= 4,09 e D = 0,91) than in the dry season (S = 26, H = 3,29 e D = 0,85), and the similarity was Ss = 55,88%. Some species, like Bacopa myriophylloides Wettst, Cyperus haspan L. ssp. juncoides (Lam.) Kük, Digitaria fuscescens (J. Presl) Henrard and Eleocharis minima Kunth, were humidity indicators, while Euphorbia thymifolia L., Wedelia brachycarpa Baker, Ludwigia octovalvis (Jacq.) P.H. Raven, Hydrolea spinosa L. were the dry ones. High values of relative covering and relative frequency of 12 species outstood, characterizing the area within both periods, with variation of these parameters between them.
Pantanal; grasslands; phytosociological structure
