Ichnofossils of flank‐buttressed trees are reported from upper Eocene coastal deposits in the Fayum Depression of northern Egypt. These ichnofossils represent the only known direct ichnofossil evidence for flank‐buttressing of trees. In living trees flank‐buttresses compensate for poor attachment to the soil surface caused by high water tables, poorly cohesive substrates or shallow soil profiles. Flank‐buttressing is confined to trees living in subtropical and tropical climates. The fossil flank buttresses support the idea that the Fayum area had a tropical climate and high water tables with low oxygen contents in the late Eocene, although it is unclear whether the fossils represent terra‐firma or mangrove forests.