8 MISCELLANEOUS CIRCULAR 92, U. S. DEPT. OF AGRICULTURE 



has adhered to the latter code in dealing with the technical names of 

 trees. The exception is the abandonment of duplicate binomials 

 such as Sassafras sassafras not because they are untenable but 

 because they represent a grotesque extreme. Practically all members 

 of the Department of Agriculture using plant names are in accord 

 with this departure. 



Fortunately the two codes are substantially in agreement on 

 several very important points. One of these points is maintaining 

 the oldest specific name applied to a plant, regardless of whether it is 

 found under the correct genus, thus eliminating the objectionable 

 usage of adopting only the specific name first combined with the 

 correct genus. Failure by some authorities to recognize the oldest 

 specific name, even though found in an incorrect genus, has caused 

 much confusion in the past, because such arbitrary practice may 

 unjustly neglect maintaining the oldest specific name of a tree. 



Another very important point of agreement is adherence now to 

 the rule of not forming a binomial by raising the third term of a 

 trinomial, the varietal name, to specific rank, even though the 

 trinomial represents the oldest name applied to a plant. Thus, the 

 oldest technical name of the Swamp White Oak is Quercus prinus 

 platanoides La Marck (1783). Under an old rule, this trinomial 

 was converted into Quercus flatanoides (LaMarck) Sudworth, which, 

 in strict compliance with the law of priority, represents the oldest 

 name for this tree. But under the recent American and Inter- 

 national rules it becomes necessary to discard this name for Quercus 

 bicolor Willdenow (1801), the oldest published binomial applied to the 

 Swamp White Oak. 



Distressing changes in some of the technical names of our trees 

 are made necessary by a careful study of the type specimens on 

 which it was long supposed rested such familiar names as Tilia 

 americana Linnaeus, and Quercus prinus Linnaeus. As a result of 

 these studies, the above-mentioned names must now disappear or 

 be shifted to other species long known by still other familiar names. 



In previous years, the desire to restore the oldest tenable generic 

 name applied to a group led to the unearthing of a few such genera 

 and to the transference to them of species that were previously 

 associated with genera of later date. The present American rule, 

 however, of not recognizing a genus for which its author had failed 

 to indicate a tv'pe species, has resulted in discarding a few of these 

 oldest genera and in the return of later properly constituted genera. 

 These changes have usually restored to use more familiar generic 

 names. A case in point is that of the silverbell trees, long known as 

 species of the genus Halesia Ellis, which was published in 1759. The 

 discoA^ery, however, some 15 years ago, that Patrick Browne de- 

 scribed a Jamaican tree under the genus Halesia in 1756 seemed then 

 to invalidate further use of Halesia, for the silverbell trees. The 

 genus Mohrodendron Britton was therefore created for these trees, 

 and under it they were maintained until recently. The discovery 

 that Patrick Browne did not indicate a type species for his genus 

 Halesia, invalidates its former standing and now permits the later 

 Halesii of Ellis to be applied, as it was previously, to the silverbell 

 trees. 



