Several permineralized dicot leaf fragments, up to 19 mm long, have been found in close association with fruits, stems and roots of Decodon allenbyensis Cevallos-Ferriz et Stockey in the Middle Eocene Princeton chert of British Columbia, Canada. Leaves are 70 mm wide at the lamina and mid-ribs are approximately 235 mm thick with a prominent C-shaped midvein. Adaxial epidermis is composed of rectangular cells and lacks enlarged mucilage cells. Leaves are dorsiventral with a double palisade layer that is slightly thicker than the spongy mesophyll. Vascular bundles possess sclerenchymatous bundle sheaths. The abaxial epidermis is made up of cells with prominent papillae that are not observed on the mid-rib. Abaxial leaf surfaces are infected by fungi that form black-colored stromata. The fossil leaves are similar to leaves of Myrtales and are compared closely to those of Lythraceae sensu lato. Leaves share most anatomical similarities with Duabanga grandiflora (Duabangoideae). Vascular tissues, palisade and spongy mesophyll, bundle fibers, and abaxial epidermal papillae are all similar to the fossil leaves from the Princeton chert. Duabanga grandiflora, however, shows adaxial mucilage cells and a more pronounced abaxial midrib than those of the fossil leaves. Duabanga, previously placed in Sonneratiaceae, has been considered part of Lythraceae by several workers. Although recent phylogenetic analyses place Duabanga and Decodon in separate clades within Lythraceae, relationships between clades are not well supported. Therefore, these fossil leaves help to examine relationships between these groups using anatomical characters. Further fossil reconstruction including documentation for attachment of leaves to the Decodon allenbyensis vegetative body will help to test phylogenetic hypotheses.

Key words: Decodon, Duabangoideae, Eocene, leaf histology, Lythraceae, Sonneratiaceae