© 1970 by Institute of Chartered Foresters
Pedunculate and Sessile Oak (Quercus robur L. and Quercus petraea (Mattuschka) Liebl.)
A Review of the Hybrid Controversy
The Nature Conservancy, Merlewood Research Station
Early nineteenth-century studies of variation in the genus Quercus L., particularly those relating to Pedunculate and Sessile oak by Lasch and Greville, illustrate the confused situation that awaited the forest botanist. Attempts of that period and later to explain this condition led to the general acceptance of a theory of unlimited hybridization and introgression between the two species. Experimentation and observations between the thirties and fifties of the present century by Dengler, Høeg, Jones, and others demonstrate the weakness of this popular concept— hence the controversy. More recent investigations by Johnsson and Krahl-Urban, supported by the biometric research of Cousens, Carlisle, and Brown, have helped in the production of a more accurate picture of the form and extent of hybridization. A great deal still remains to be done to elucidate the natural frequency of F1 hybrids, and backcrossea in different regions. The karyotypes of both species and hybrids have still to be defined.