Sexual reproduction of beeches is the subject of surprisingly few studies. Here is one of the few:
“Natural interspecific hybridization between sexual and apogamous species of the beech fern genus Phegopteris Fée,” Gerald A. Mulligan, Lionel Cinq-Mars, William J. Cody, Canadian Journal of Botany, 1972, 50(6): 1295-1300.
BONUS: Phegoperis Fée