TAXONOMY OF THE HIGHER PLANTS 1 93 



Thus taxonomy, as has been aptly remarked, is at once the alpha and omega 

 of biology. 



What has happened in plant taxonomy, the oldest of the botanical dis- 

 ciplines, during the past fifty years, the lifetime of the Botanical Society 

 of America? It matters little whether we call it the new systematics, biosys- 

 tematics, or the new taxonomy, we cannot fail to recognize that there have 

 been significant changes during this period. Perhaps the rise of genetics, with 

 its important impact on taxonomy, has had the most far-reaching influence, 

 but there have been other changes within the subject itself. In the following 

 essay, I propose to point up some of the characteristics of the taxonomic field 

 and its relationship to other branches of botany and to stress some of the 

 changes during the past fifty years that seem significant. 



At the outset, it should be made clear that certain aspects of plant taxon- 

 omy are concerned ultimately with the individual plant. And the finite life of 

 every individual plant, whether it be a small, ephemeral herb that completes 

 its life cycle from seed to maturity in a few weeks or a giant redwood that lives 

 for a thousand years, is tied into a line of descent. Within each descent line 

 are contained and propagated the determinants and strictures of the total 

 nature of each individual. And there is a certain permanency about each such 

 descent line even though constancy is not a necessary feature. The degree of 

 constancy and of permanency is dependent on a large number of factors and 

 differs widely from one line of descent to another. 



The number of relatively discrete present-day end points of descent lines 

 of plants on the earth's surface presumably corresponds somewhat to the 

 number of species. However, these lines are of an extremely complex origin, 

 often formed by the fusing of two or several different lines. For this reason, 

 the picture of the evolutionary relationships of our modern species of plants 

 takes the form of a reticulum with anastomosing descent lines reaching far 

 into the past. The very difficult task of the taxonomist is that of discovering 

 these end points, their origins and connections, together with the presentation 

 and codification of information concerning them. The genetical interrelation- 

 ships of living individuals within a population, of populations of individuals 

 within a given taxon,^ and of the members of different taxa are primary 

 considerations. 



One of the most dynamic aspects of taxonomy is the study of populations 

 of living plants to establish the variation patterns present. This type of study 

 provides a rich source of understanding of a given taxon, and when these 

 patterns are properly evaluated, in terms of their repetition and geographical 

 spread, they are at the base of the taxon's proper definition. Thus variation 



^ The word taxon has come into general use in a very short time. It is used to 

 refer to any taxonomic category or group without specifying which one. For ex- 

 ample, species, genera, families, etc., are all taxa. 



