Evolution is often equated with natural selection and is taught from a primarily functional perspective while comparative and historical approaches, which are critical for developing an appreciation of the power of evolutionary theory, are often neglected. This report describes a study of expert problem-solving in phylogenetic tree construction. Results from that study are then used to describe problems in this domain and factors that govern problem difficulty. A problem-based approach to the teaching and learning of evolution was considered. Three series of research problems were constructed that varied the numbers of solutions, taxa, and characters. Each problem consisted of a matrix of coded and polarized phylogenetic data organized by taxa and characters. Nine expert phylogenetic systematists participated in the research project by thinking aloud while constructing phylogenetic trees to account for the problem data matrices. All of the experts agreed that the problems were a realistic characterization of the concepts and processes central to their discipline. Simple tree construction problems such as these allow students to become familiar with the processes used by scientists to explain evolutionary history. The appendix contains a primer of phylogenetic assumptions, diagrammatic elements, and terms. Contains 15 references.(PVD)