A new plant from the Los Ahuehuetes locality, near Tepexi de Rodríguez, Puebla, Mexico, is described based on its leaves. They are characterized by being ovate to elliptic, 4.5 cm long by 2.1 cm wide, having an entire margin, eucamptodromous venation, a midvein that is slightly curved and attenuated towards the leaf apex, seven pairs of secondary veins diverging at an acute angle from the midvein, percurrent tertiary veins forking or sometimes reticulated forming areoles, and having a petiole 1.3 cm long and 0.3 cm wide. An agglomerative nonhierarchical analysis with average linkage, based on the definition of 41 character states in 18 operational taxonomic units allows distinction between Karwinskia, Berchemia, and Rhamnus; the recognition of an extinct monotypic genus, Berhamniphyllum; and the identification of two fossil species of Karwinskia, among which the new plant from Puebla, Karwinskia axamilpense Velasco de León et al., is well defined. This new fossil leaf not only adds to the recently known Tertiary plants of the Los Ahuehuetes locality, but it gives new insights into the past flora of tropical North America and further supports the long history of some neotropical endemics, suggesting that, during the Tertiary, at least some areas in southern latitudes of North America could have been important for the origin and radiation of some taxa.

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