The growing number of biogas plants in Germany has greatly increased the demand for maize silage, the predominant crop used for biogas production. With a share of 80% among the energy crops, maize silage is currently subject to major concerns such as competition between food and fuel, environmental issues and sustainability. Alternative substrates cannot compete with the specific methane yield (SMY) of maize and are therefore disadvantaged. The cup plant is considered suitable to provide a solution however little data is available. To support the search for alternative crops, batch and continuous laboratory tests were carried out in order to determine the SMY of cup plant silage. The mean SMY in the batch test was measured at 0.251 +/- 0.0141 m(N)(3)/kg oDM and at 0.227 +/- 0.0158 m(N)(3)/kg oDM in the continuous test. The results show that the methane yield per ha of cup plant lies in the range between grass and maize silage. The cup plant proved to have no negative effects on process stability for the ratio fed into the digester. Although cup plant cannot currently compete with maize silage, further research in plant breeding will help to increase dry matter yields, SMY potential and promote the positive environmental effect such as a diverse energy crop rotation. (C) 2015 Elsevier Ltd. All rights reserved.