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Abstract

Student understanding of biological representations has not been well studied. Yet, we know that to be efficient problem solvers in evolutionary biology and systematics, college students must develop expertise in thinking with a particular type of representation, phylogenetic trees. The purpose of this study was to understand how undergraduates make sense of phylogenetic representations presented in a plant systematics course designed to promote student tree thinking expertise. The primary data sources were two-tiered pre/posttests and interviews with key informants. Using observations and document analysis as supporting data, we identified multiple misconceptions within students' knowledge of systematics not previously identified in the literature. Relying upon these misconceptions, students developed alternative types of reasoning that interfered with interpreting and using trees. We constructed a classification of student reasoning and identified a suite of varying levels of approaches that went beyond misreading the topology of phylogenetic trees to include the persistent use of nonevolutionary reasoning to address phylogenetic problems. We categorized student reasoning as extraneous, ecological, morphological, branch influenced, tree shape influenced, node influenced, limited phylogenetic, and phylogenetic. By better understanding our students reasoning by qualitative assessments, these findings have implications for curriculum, instruction, and assessment strategies. © 2011 Wiley Periodicals, Inc. Sci Ed95:794–823, 2011