The Development of an Operational Approach in Plant Taxonomy

Abstract

PARTICULARLY within the last decade, though occasionally before this for 100 years or more, voices have been raised in protest against some of the postulates and involvements of Linnaean taxonomy. Though these arguments have been primarily philosophical-stating in various ways that the species concept and the hierarchical arrangement of categories are subjective and illogical-they have become more practical today. The system is becoming increasingly burdened. Perhaps 350,000 species of plants have been described. Each has been named, on the average, several times. The descriptions of many of them, originally brief morphological sketches, are being increased with cytological, genetic, chemical, ecological, and other types of data. Reshuffling of names and even categorical assignments increase as the number of taxonomists and the amount of work they do increase. Trying to keep order in this impending chaos taxonomists follow a set of rigid, conservative rules which change less and less as our knowledge of plants grows greater and greater. The working taxonomist-the monographer-finds himself now called upon to make hundreds or thousands of decisions regarding characteristics to be studied, sampling techniques, proper statistical treatments of data, assignment to categories, etc. Nearly all of these are intuitive or value judgments. He must choose certain characters, certain sampling techniques, etc., and he has many of each to choose from. What guides him in his choices? In the time of Linnaeus it was the socalled constancy of characteristics-as, in a way, it still is for most taxonomists. In defining a class of objects such as Quercus alba L., the white oak, the taxonomist attempts to find characteristics among the individuals studied which are the same or nearly the same in all the individuals, avoiding those characteristics which vary widely from plant to plant. For this reason Linnaeus and virtually all his successors have been predominantly concerned with certain reproductive features, such as the number and arrangement of the stamens and the parts of the pistil. Today we have more sophisticated methods of study, but I believe that we still continue to stress similarities and avoid differences, even in such modern studies as those upon chromosome number, pigmentation, physiological reactions, etc. What is a rational explanation for this approach? In the time of Linnaeus and nearly until that of Darwin, 100 years ago, it was commonly believed that God had created separately kinds or species of living things upon the earth-that though we could not avoid seeing overlap among them, this overlap had been derived subsequently to their creation. It was therefore believed that each species could be found and identified by a thorough search: its original core of characteristics could be reconstructed. The species originally was an idea in the mind of God. This philosophical approach-as has often been pointed out-can be traced to Aristotle, thence to Plato, and presumably backwards in history to early man when verbal communication was first developed. At least we find that our most primitive savage tribes today have it.