TAXONOMIC PRINCIPLES 15 



Any hypothetical arrangement purporting to show phyletic 

 relationships, whether based on cytogenetical, biochemical, morph- 

 ological, or a combination of such data, although of limited value in 

 itself, may be catalytic in the sense that it elicits further speculation 

 and wider associations or suggests preferred additional investigation. 

 In fact, it has succeeded if it has merely received sufficient attention 

 to persuade its declaimers to crystallize their own position and re- 

 appraise the total evidence. Of course, a parade of tenuous and 

 vacuous theories of trivial nature is to be discouraged, but most 

 of this type are rather easily perceived by the competent systematist. 



Prior to Darwin's publications there were few, if any, pur- 

 portedly phylogenetic systems of classification proposed by the 

 serious plant taxonomist, for so long as taxonomists accepted the idea 

 of special creation, they were not likely to be concerned with phy- 

 logeny. While several outstanding taxonomists during the 1800's 

 classified plants by a "natural" system, they often made no serious 

 or conscious attempt to place the major taxa together according to 

 their evolutionary relationships. For example, such outstanding 

 workers as Bentham and Hooker, in their classic Genera Plantarum, 

 placed the gymnosperms between the dicots and monocots instead of 

 placing the latter two together as most phyletic workers have done 

 since that time. Nonetheless Bentham and Hooker's work remains to 

 this day a useful system, mostly "natural," but not phylogenetic. 



Much has been written about the speculation involved in 

 numerous attempts by taxonomists to show phylogenetic relation- 

 ships at various taxonomic levels. While most workers concede that 

 it is possible to hypothesize with considerable assurance at the generic 

 and specific level, mainly because these lower categories are suited to 

 experimental, cytogenetical, and populational study, they also rec- 

 ognize that attempts to construct phylogenetic classifications at the 

 higher taxonomic levels often involve highly subjective judgments. 

 The fact that it becomes more difficult to position taxonomic groups 

 with respect to each other at the higher taxonomic levels in no way 

 invalidates the objectives sought, and the admission that this can 

 be done at the lower levels, in principle at least, assures the worker 

 that attempts to do this with the higher categories are fundamen- 

 tally sound. 



Some workers have despaired of ever achieving any stable^ 

 or useful phylogenetic classification and have argued for a system 

 that is both reasonably "natural" and useful but without phyletic 



3 Many persons concerned with taxonomic problems, not necessarily taxonomists 

 themselves, deplore the repeated rearrangements of taxa that appear necessary as new in- 

 formation accumulates. Let us suppose a species, long placed in a particular genus, after 

 careful study is found to belong to some other genus. Under a set of international rules, 



