A remarkable fossil plant assemblage from the lowermost Oligocene Haselbach horizon (Gröbers Member, Böhlen Formation) was excavated at the Vereinigtes Schleenhain opencast mine (northwestern Saxony, Germany) and is described herein. The lower unit of the Haselbach horizon represents abandoned channel deposits that contain masses of Zingiberoideophyllum liblarense leaves. Species identification of the leaves is based on morphological characters and micromorphological features of the cuticle. Other plant organs of the previously described whole plant Spirematospermum wetzleri-Zingiberoideophyllum liblarense, such as fruits, seeds, rhizomes, and rootlets, were also observed on associated bedding planes, which supports this whole-plant reconstruction. The other megafossil remains in this taphocoenosis, mostly leaves, are identified taxonomically and interpreted as being derived from a mixed softwood and hardwood riparian forest of Acer haselbachense, Apocynophyllum neriifolium, Carpinus grandis, Engelhardia orsbergensis, Populus germanica, Rosa lignitum, Taxodium dubium, and from a Nyssa-Taxodium swamp. Based on the plant taphonomy and the paleoecology of the plants, this plant assemblage was likely deposited in still water and therefore mainly parautochthonous. Vertical changes in the composition of the plant assemblage, in particular the disappearance of the Zingiberoideophyllum liblarence leaves, are attributed to changes in habitat, such as alterations in the soil substrate and/or rising water levels. Taphonomic and paleophytosociological aspects of the assemblage confirm the previously published autecological reconstruction of the Spirematospermum wetzleri-Zingiberoideophyllum liblarense whole plant as an aquatic subshrub growing in shallow standing water, most likely in monotypic dense stands or in association with the Apocynophyllum neriifolium-Microdiptera whole plant. Nomenclatural and taxonomic problems of the family assignment of Zingiberoideophyllum liblarense are discussed briefly. The presence of transverse veins, also called cross veins, suggests an assignment to Zingiberaceae and excludes it from Musaceae.