Numerical Taxonomic Studies of Hybridization in Quercus. II. Populations with Wide Areal Distributions and High Taxonomic Diversity

Abstract

Two populations of Quercus subgenus Erythrobalanus, one from Tennessee and the other from Ohio, were analyzed by cluster analysis and principal component analysis. Each contained one or more putative hybrids and exhibited high diversity in the number of included taxa and in the areal distributtion of the inclutded individ- uals. The results indicate that in sutch poputlations the nutmerical methods employed may not provide accurate estimates of the origin of putative hybrids. narrow areal distributions and low taxonomic diversity. Each population contained, in addition to various species of Erythrobalanus, several opera- tional taxonomic units (OTU's) identified in the field as putative hybrids. The studies were designed to analyze the putative hybrids with respect to all species of Erythrobalanus that might be possible parental taxa. Unlike earlier studies of oak hybrids (e.g., Stebbins et al., 1947; Cooperrider, 1957), in which the putative hybrids were compared only with two species assumed a priori to represent the parental taxa, our analyses were based on com- parisons of putative hybrids with all species of Erythrobalanus growing in the immediate area. Furthermore, our analyses were based on 63 characters as opposed to the restricted data sets used in previous studies. We believe that analyses using large sets of characters and including all species in the area provide a better estimation of the probable parentage of naturally occurring putative hybrids. The analyses presented earlier were almost ideal because of the nature of the populations. Each population was confined to a small area and was composed of a few species and, except for the New Jersey population, only two species appeared to have been involved in the production of the putative hybrids. This relative homogeneity greatly facilitated the analyses and allowed fairly precise identifications of the parentage of the putative hybrids.