The morphology and anatomy of a new zygopterid fern are described from the Middle Pennsylvanian (Bolsovian) of Floha, SE Germany. The fossils occur as allochthonous remains within the basal Schweddey Ignimbrite, which preserves a diverse wetland plant community of cordaitaleans, ferns, pteridosperms, calamitaleans, and lycophytes. Pinnae of Alloiopteris loecsei sp. nov. exhibit a combined carbonized and anatomical preservation type due to rapid entombment in fine-grained pyroclastics. The newly collected Alloiopteris fossils show typical gross morphology, but also reveal the anatomy of penultimate and ultimate rachides. The affinity of the new fern is discussed amongst zygopterids in general and the famous zygopterid stems Zygopteris primaria (von Cotta) Corda and Asterochlaena laxa Stenzel from the Floha site in particular. Our investigation highlights the striking potential of pyroclastic deposits for preserving and yielding both morphological and three-dimensional anatomical aspects of plant fossils.