A NUMERICAL TAXONOMIC STUDY OF THE GENUS PLATANUS BASED ON MORPHOLOGICAL AND PHENOLIC CHARACTERS

Forty-two morphological and eighty chemical (phenolic) characters were employed on a numerical taxonomic study of the genus Platanus. Ten taxa were used for morphological study, and nine were available for chemical study. UPGA was employed for cluster analysis; correlation coefficients served as a measurement of the similarity between each OTU-pair. Comparison was made for phenograms and graph diagrams of nine taxa based on morphological characters with those based on chemical characters. It has been found that the two agree with each other in many respects. Correlation coefficient between similarity matrices based on morphological and chemical characters is 0.573. The result generally supports the belief that taxa closely related on morphological grounds are similar biochemically. A systematic consideration of the genus has been made, based on the information available. A CLASSIFICATION of organisms is generally aimed at the recognition of a "natural" system. Since the advent of the evolutionary theory, a majority of systematists have come to consider a natural classification to be synonymous with a phylogenetic classification. However, a complete fossil record is required in order to establish phylogenetic relationships with some certainty. In the absence of fossil records, phylogenists must accordingly "trace" phyletic relationships using inferences from phenetic information. Of the phenetic information available, usually only those characters assumed to be important for phyletic consideration are chosen. For each such "important" character, additional assumptions have to be made on the primitive or advanced stage of character states. Since the degrees of importance and primitiveness of characters are usually based on the worker's subjective perception and cannot be proven objectively, systematic arrangements of organisms based on these procedures have often been criticized as more art than science. Following Gilmour (1937, 1951), Sneath (1957) proposed that, since a true phylogenetic classification is unobtainable in most cases, a natural classification should be one which contains the greatest amount of information and, therefore, as many characters as possible should be employed. Since the appearance of numerical taxonomy, a number of articles have been published on the 1 Received for publication 20 November 1972. This paper is based on a portion of a thesis submitted in partial fulfillment of the requirements for the Ph.D. degree at the University of Pennsylvania. The author is grateful to Dr. H. L. Li, the major advisor on this study, for encouragement and guidance, to Dr. J. Mears for his guidance in carrying out the biochemical part of this investigation, and to Dr. W. W. Moss for his guidance on the numerical taxonomic study. classification of the flowering plants, employing numerical taxonomic approaches based on morphological characters (e.g., Morishima and Oka, 1960; Heiser, Soria, and Burton, 1965; Solbrig, 1970). Numerical taxonomic approaches have also been employed in the presentation of biochemical data by several workers, e.g., Parups et al. (1966) on the flavonoids of Trifolium; Stone, Adrouny, and Flake (1969) on the nut oils of Carya; Adams and Turner (1970) on the terpenoids of the populations of Juniperus ashei; and Adams (1972) on the populations of Juniperus pinchotii. Employing both chemical (terpenoid) and morphological characters, Adams and Turner (1970) and Adams (1972) demonstrated some correlation between relationships of populations based on terpenoid characters and those on morphological characters. As far as I am aware, no numerical taxonomic studies on flowering plants have been published employing both morphological and phenolic (or flavonoid) characters. This report is such a study of the genus Platanus (Plane trees or Sycamores, Platanaceae). Its main purpose is to compute and compare phenetic relationships based on morphological characters with that based on phenolic characters. The results of the numerical study, especially from morphological data, are used for a systematic consideration of the genus. MATERIALS AND METHODS-The OTUs-As this study was aimed at an assessment of phenetic relationships at the species and variety levels, populations at these levels were chosen as the Operational Taxonomic Units, OTUs (Sokal and Sneath, 1963). The total number of OTUs was ten for morphological characters, whereas nine