In a Plant Microbial Fuel Cell (P-MFC) three plants were tested for concurrent biomass and bio-electricity production and maximization of power output. Spartina anglica and Arundinella anomala concurrently produced biomass and bio-electricity for six months consecutively. Average power production of the P-MFC with S. anglica during 13 weeks was 16% of the theoretical maximum power and 8% during 7 weeks for A. anomala. The P-MFC with Arundo donax, did not produce electricity with a stable output, due to break down of the system. The highest obtained power density in a P-MFC was 222 mW/m(2) membrane surface area with S. anglica, over twice as high as the highest reported power density in a P-MFC. High biomass yields were obtained in all P-MFC's, with a high root:shoot ratio, probably caused nutrient availability and anaerobia in the soil. Power output maximization via adjusting load on the system lead to unstable performance of the P-MFC. (c) 2010 Elsevier Ltd. All rights reserved.