In this study it was evaluated changes in situ in root and leaves of Eicchornia azurea, an invasive macrophyte of worldwide reservoirs, in a gradient of organic matter provided by allochthonous and autochthonous sources at Medalha bay, Pantanal, Brazil. The results showed that the greater the distance of riparian vegetation and sediment, the greater length, dry weight of roots and lower the distance between their insertions. The leaves did not present dry weight differences in the gradient. It was conclude that these macrophytes optimize the root morphology to absorb nutrients along a gradient of organic matter.Key words: E. azurea; aquatic macrophytes; phenotypic plasticity. ResumoNós avaliamos alterações in situ em raízes e folhas de Eicchornia azurea, macrófita invasora de reservatórios no mundo todo, em um gradiente de matéria orgânica formado por fontes autóctones e alóctones na Baía da Medalha, Pantanal, Brasil. Quanto maior a distância da mata ripária e do sedimento, maior o comprimento, peso seco das raízes e menor a distância entre suas inserções. As folhas não apresentaram pesos secos diferentes ao longo do gradiente. Provavelmente estas