The Late Oligocene (28-27 Ma) Guang River flora from northwestern Ethiopia, a well preserved, autochthonous plant macrofossil compression assemblage, is preserved in an overbank deposit and likely represents a tropical seasonally or periodically inundated riparian forest community based on taxonomic identification, leaf morphology, lateral heterogeneity, and sedimentology. This forest assemblage likely grew under slightly warmer, wetter, and less seasonal conditions than experienced on the Ethiopian plateau today based on the overlapping distribution analysis (ODA) method. Taxonomic composition of this assemblage bears both similarities and differences to modern African tropical forest communities. The Leguminosae (legumes) are species rich and dominant in African forests today and are similarly represented in the fossil assemblage. Other groups like the Arecaceae (palms) are poorly represented and species depauperate in such forests, but are both diverse and species rich in the Guang River flora. The Guang River flora also provides an example of what the composition of an 'ancestral' Africa forest community consisted of before the major division between the Guineo-Congolian and East African forests and extirpations/extinctions during the Neogene. The macrofossil assemblage, along with other near contemporaneous paleobotanical floras, supports the presence of extensive tropical moist forest in Afro-Arabia during Oligocene. The assemblage also provides evidence that the palms likely became diminished in diversity and ecologically due to a combination of Paleogene and Neogene events.