Building a Twig Phylogeny

In this classroom activity, students build a phylogeny for woody plant species based on the morphology of their twigs. Using any available twigs, students can practice the process of cladistics to test evolutionary hypotheses for real organisms. They identify homologous characters, determine polarity through outgroup comparison, and construct a parsimonious tree based on synapomorphies (shared derived characters). This activity efficiently demonstrates many systematics concepts, including homology, homoplasy (convergence and reversal), polarity, synapomorphy, symplesiomorphy, autapomorphy, polytomy, and parsimony. It also engages students in inquiry, promotes student collaboration, raises awareness of plant structure, and exposes students to the diversity of common local trees.