Living species of Fagus can be clearly distinguished by using the morphology of the cupule/nut complex, although most of the morphological characteristics display a high degree of parallelism. Therefore, a complete set of informative characters is necessary to accurately identify living species. Cluster analysis of modern taxa results in two well‐separated species groups. However, these groups do not always reflect phylogenetic relationships but include taxa that merely share characteristics of no phylogenetic significance. Character evolution in Fagus cupules appears to go from medium‐sized cupules with scalelike appendages, short peduncles, and unwinged nuts that are clearly longer than the cupule valves to either very small or very large cupules with short to very long and slender peduncles, spinelike appendages, and nuts that are as long as the cupule valves. Investigations of modern cupules demonstrate that several diagnostic characters are easily lost during water transportation. Such cupules show patterns of degradation very similar to those also found in fossil taxa and on which fossil species have been based. The three European Tertiary fossil species based on cupule/nut characteristics (Fagus deucalionis Unger, Fagus decurrens Reid & Reid, and Fagus microcarpa Miki emend. Uemura) are not clearly distinguishable but are connected by morphoclines. Accordingly, we propose to treat them as one form‐species F. deucalionis Unger emend. Denk et Meller. Fagus deucalionis also appears to be conspecific with cupules of the Central Asiatic fossil species Fagus antipofii Heer and very similar to the western North American fossil species Fagus pacifica Chaney. All these taxa are “modern” in appearance, displaying spinelike cupule appendages and conspicuously winged nuts. They resemble the modern East Asiatic Fagus crenata Blume (Japan), Fagus longipetiolata Seemen (China), Fagus tientaiensis T. N. Liou (China), and partly Fagus hayatae Palibin (China mainland, Taiwan), Fagus grandifolia (North America, Mexico), and Fagus sylvatica L. (Europe, southwestern Asia). Previously noted specific similarities between European Oligocene cupule/nut taxa and the modern F. grandifolia Ehrh., and European Pliocene cupule/nut taxa and the modern Japanese F. crenata, cannot be confirmed.