Growth, morphology, NH4+ uptake and mineral allocation in Salvinia cucullata Roxb. ex Bory grown with different amounts of NH4+ were investigated. Plants of uniform size were grown on full strength Smart and Barko medium with different NH4+ concentrations (0.5, 1, 5, 10 and 15 mM) and incubated in a greenhouse for four weeks. Salvinia cucullata grew well in the medium with 0.5-1 mM NH4+ with a relative growth rate of 0.11-0.12 d-1 without exhibiting NH4+ toxicity symptoms. With an NH4+ concentration above 5 mM, plant growth was suppressed and signs of NH4+ toxicity were observed. NH4+ toxicity symptoms were obvious in plants supplied with 10 mM and 15 mM NH4+. These plants had low growth rates, short roots, low numbers of roots and showed chlorosis. Rotted roots and stems were also found in plants fed with 15 mM NH4+. This species had a high uptake rate even though the NH4+ concentrations increased, making it an ideal candidate for growth in eutrophic environments. The high NH4+ concentration had a negative effect on K uptake resulting in low K concentration in the plant tissue, but the plants increased N content in plant tissue. Thus, harvested plants can be used as soil fertilizer or for animal feed. Furthermore, maintaining plant biomass can improve the efficiency of water treatment. © 2011 Elsevier Inc. All rights reserved.