Leaf Survival and Evolution in Betulaceae

Studies on the changes in leaf number of 12 species of Betulaceaewere carried out by repeated observations during several years.The inner structure of the winter buds of these species wasalso examined. The periods of leaf emergence were long in Alnusand Betula, intermediate in Corylus and short in Ostrya andCarpinus. A heavy summer leaf fall is characteristic only ofthe Gymnothyrsus subgenus of Alnus. One lamina and two stipulesis the basic unit constituting the winter buds. Only the budsof Gymnothyrsus are composed of several of these units. In theAlnaster subgenus of Alnus, Betula and Corylus, there are oneor two scales that seem to have originated from the two stipulesremaining after reduction of the lamina. Eight and 24 scalesof similar origin were found in Ostrya and Carpinus respectively.A common ancestral species having the following primitive charactersis proposed: shoot constituted only of the equal-sized units,period of leaf emergence long, and leaf fall usually occurs.Alnus (Gymnothyrsus) is assumed to be the most primitive typeas it has many characters similar to those of the proposed ancestralspecies. Carpinus is assumed to be the most advanced group.The leaf survivorship curve is assumed to have changed fromthe primitive bell-shaped to an advanced trapezoid concurrentwith an increase in the number of bud scales. Betulaceae, Alnus, Betula, Carpinus, Corylus, Ostrya, leaf survival, leaf emergence, stipules, winter buds, evolution