SHAPE CHARACTERS IN NUMERICAL TAXONOMY AND PROBLEMS WITH RATIOS

Publisher Website
Google Scholar
Abstract
Summary: Systematists in general, and those applying numerical methods in particular, frequently use ratios to express the shape of plant organs in order to standardize for size. However, ratios may have undesirable statistical properties and do not accurately represent the change in shape that occurs during development. Because of changes in allometric growth during development, ratios are often highly correlated with size and thus may not be effective methods of standardization. The slope of the regression line is a better measure of certain aspects of shape, and the intercept of the line can in some cases provide additional valuable information for comparative purposes. Difficulties associated with using regression analysis include the requirement for a reasonable sample size, increased computational expenses, and the disposition of cases where a low regression coefficient is obtained. Shape characters defined by regression analysis for cladistic inference may also be more suitable than ratios.