THE ANCIENT OAKS OF AMERICA 



WILLIAM TRELEASE 

 University of Illinois 



While studying the oaks which are now so striking a component of 

 the vegetation of North America, I have found it necessary to form 

 some idea of the history of Quercus before our own day. Neither time 

 nor opportunity has offered for basing this on a reexamination of the 

 scattered materials that have served for the classic studies of Les- 

 quereux and Newberry, or for the later work of Hollick, Knowlton, 

 Berry and Cockerell; but from a careful examination of descriptions 

 and illustrations I have tried to bring into some sort of orderly as- 

 semblage the scattered facts that have been observed and described (i). 



So far as I know, only two of our fossil species {Q. consimilis and 

 Q. pancidentata, both of the Eocene) are known in fruit (2) ; the others, 

 though exceptionally with twig remnants, are represented usually by 

 dissociated leaves, sometimes well preserved but frequently only in 

 fragments showing little detail. These materials have been referred 

 to Quercus because of the general appearance and especially the 

 venation of the leaves when this is ascertainable. It is not sur- 

 prising that misapprehension should have existed occasionally as to 

 the age of clay and similar deposits in which some have been found, 

 or that some of them should have been transferred to genera of other 

 families, even, as a result of further study; indeed a considerable 

 number of these fossils appear to have been called oaks rather because 

 they could be called nothing else than for any very positive other 

 reason (3). 



When the American fovssils were first studied, the genus Quercus 

 was made to include a number of forms that are segregated now in 

 the genus DryophyUum (4), held to be prototypic of the family Fagaceae 

 rather than of its dominant genus, Quercus. The natural early tend- 

 ency, as would be expected of conservative and experienced botanists 

 working with isolated and fragmentary leaves, was to stretch the 

 limits of species so as to recognize identities of Old and New World 

 species, rather than to see dependable differences in such a repre- 

 sentation, especially in a genus recognized as unusually variable in the 

 foliage of even individual trees of existing species. None of the 

 recently described species has been identified with a European form, 

 and most of the earlier identities have been discarded, sometimes by 



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