HYBRID OAKS 



BY GEORGE B. SUDWORTH 



HYBRID oaks of this country are exceedingly in- 

 teresting trees. They are the result of a natural 

 crossing of two different species of oaks and, 

 as a rule, they are strikingly distinct trom other oaks 

 in the peculiarly mingled characteristics of the parent 

 species. Their distribution is very irregular, so that 

 our knowledge of the ranges of the different forms is 

 incomplete. 



In all, there are approximately twenty different 

 hybrid oaks now known. Nineteen of these inhabit 

 Eastern United States, only one being known in the 

 Pacific region, 

 and none hav- 

 ing been dis- 

 covered in the 

 Rocky Moun- 

 t a i n Region* 

 The fact that 

 60 per cent of 

 the forty-eight 

 native species 

 of oaks grow 

 in the East 

 may partly 

 account for 

 the c o r re- 

 s p o n d ingly 

 greater n u m- 

 ber of hybrid 

 oaks discover- 

 ed in that 

 part of the 

 country, 

 ,/here n e c e s- 

 sarily there 

 would be 

 greater oppor- 

 tunity offered 

 for crosses. 



There is no 

 record of the 



crossing of white oaks and black oaks, all of the hybrid 

 forms now known having been produced by crosses only 

 between members of each of these two distinct tribes. 

 Whether or not there is any inherent barrier to hybridi- 

 zation between white oaks and black oaks in the fact 

 that the white oaks are annual fruiting trees and the 

 black oaks are biennial fruiting species, is unknown. 



A much larger number of black oak hybrids has 

 been discovered than of white oak, there being sixteen 

 black oak hybrids recorded and only four of white oak 

 parentage. Whether or rot the black oaks have a 



Dr. William Trelease records ( Proc Am. Phil, Soc. LVl, 4, 1917), the 

 found in the southern Rocky Mountain Region. His very excellent paper 

 published hybrids which were unknown to me when this article went to j 



FIG. 1. MATURE FOLIAGE AND ACORNS OF THE NEW HYBRID. 



It will be seen that the shape and size of the leaves are very like those of the red oak, though many of 

 them resemble Ihc black oaK more closely in shape, color and texture. The mature acorns are of the 

 same general shape, though smaller, than those ot the 'red oak. 



greater tendency to hybridize than do white oaks, is 

 unknown. The relatively more frequent association of 

 different black oaks than is the case with white oaks 

 may also be a determining factor in the greater occur- 

 rence of black oak hybrids. 



The determination of what parent species of oaks 

 have produced the various hybrids now known is a 

 matter entirely of recognizing the distinguishing char- 

 acteristics of the parents as exhibited in the hybrid. No 

 one is prepared to prove the supposed parentage of any 

 of the hybrid oaks, and obviously because the crossing 



of the parent 

 trees occurred 

 without the 

 aid of man. So 

 far, no one ap- 

 pears to have 

 tried artificial- 

 ly to repro- 

 duce any of 

 these hybrid 

 forms by 

 cross - fertili- 

 zation of their 

 supposed par- 

 e n t s. It is 

 true, of course, 

 that plant 

 breeders in 

 this country 

 have had little 

 or no incen- 

 tive for cross- 

 ing oak trees, 

 because with 

 the great vari- 

 ety of com- 

 mercially use- 

 ful species now 



available there 

 would seem to be no pressing need of seeking new and 

 better forms. Systematic botanists have contented them- 

 selves with naming and describing hybrid oaks just as 

 they were found in nature, and have relied upon their 

 judgment in determining the parentage. It is a note- 

 worthy fact, however, that there is considerable differ- 

 ence of opinion among botanists as to the parentage of 

 certain hybrid oaks. Thus, the parentage of one of the 

 best known of our hybrid oaks, the Bartram Oak, first 

 named Quercus heterophylla, has varied with the author 

 from that of Quercus phellos x velutina and Q. phellos x 



existence of "Q. arizonica x grisea Q organesis", which was doubtlers 

 on "Naming Hybrid Oaks" also lists a number of apparently hitherto ur- 

 reas. 



083 



