A novel, strictly anaerobic, methanogenic archaeon, strain E03.2^T, was isolated from a full-scale biogas plant in Germany. Cells were non-motile sarcina-like cocci, occurring in aggregates. Strain E03.2^T grew autotrophically on H₂ plus CO₂, and additionally cells could utilize acetate, methanol, moni-, di- and trimethylamine as carbon and energy sources; however, growth or methanogenesis on formate was not observed. Yeast extract and vitamins stimulated growth but were not mandatory. The optimal growth temperature of strain E03.2^T was approximately 45 °C; maximal growth rates were obtained at about pH 7.0 in the presence of approximately 6.8 mM NaCl. The DNA G+C content of strain E03.2^T was 41.3 mol%. Phylogenetic analyses based on 16S rRNA gene and mcrA sequences placed strain E03.2^T within the genus Methanosarcina. Based on 16S rRNA gene sequence similarity strain E03.2^T was related to seven different species of the genus Methanosarcina, but most closely related to Methanosarcina thermophila TM-1^T. Phenotypic, physiological and genomic characteristics indicated that strain E03.2^T represents a novel species of the genus Methanosarcina, for which the name Methanosarcina flavescens sp. nov. is proposed. The type strain is E03.2^T (=DSM 100822^T=JCM 30921^T).