An Estimate of Phylogenetic Relationships within the Genus Crusea (Rubiaceae) Using Character Compatibility Analysis

Abstract

The seventeen taxa (thirteen species and four varieties) in the genus Crusea, as recognized by W. R. Anderson, are described with fifty-eight qualitative characters. A priori estimates of the directions of evolutionary trends among the character states of each character are made. The patterns of agreement and disagreement among these fifty-eight cladistic characters were revealed using Character Compatibility analysis. A large collection of mutually compatible characters was chosen to form the basis foran estimate of phylogenetic r-elationships. This estimate was then further refined within the major phyletic lines suggested, by fur-ther studying the patterns of agreement among characters within these lines to enlarge the collection of mutually compatible characters with compatible secondary characters. Finally, characters of special interest such as annual vs. perennial, and flower color are discussed in the context of this estimate of phylogenetic relationships. The estimation of evolutionary relationships has long been a part of comparative biology. Recently, the interest of plant systematists in meeting this challenge has increased. Takhtajan (1969), Boulter et al. (1972), and Sporne (1975) provide three recent examples of estimates of evolutionary relationships for the angiosperms as a whole. Examples at the level of genus or family (except as suggested by the recognition of sections, subfamilies etc.) are not yet common. This is perhaps explained in part by our realization that such estimates usually contain a large component of uncertainty. Indeed, Hughes (1976) argues that estimates based on neobotanical data are nearly worthless. In contrast, we feel that the best estimate of a specialist may be better than no estimate at all, especially when the data, principles, and procedures with which this estimate was achieved are clearly presented. Several principles and procedures for estimating evolutionary relationships have been presented and discussed in the recent literature. Some of these are explained by Estabrook (this volume) and reviewed by Funk and Stuessy (this number). Here we wish to provide an example of the application of compatibility analysis to the estimation of evolutionary relationships among the taxa of the genus Crusea. A technical explanation of the procedures is given by Estabrook (et al. 1975, 1976a, b), an application in zoology is presented by Estabrook et al. (1977), and other related discussions are made by McMorris (1975, 1977) and Estabrook and McMorris (1977). l University Her-barium and Botany, University of Michigan, Ann Arbor, MI 48109.