The amino acid permeases (AAPs) are a family of proton-coupled amino acid transporters that are found throughout the land plants but not in algae. Previously, the majority of research done on AAPs has been in Arabidopsis thaliana and other eudicots. There is a wide variation in the number of AAP genes between plant species, so some AAPs in non-eudicot species might have novel functions. The purpose of this thesis was to investigate the function of AAPs in rice, a model monocot, and liverwort, a basal land plant. The long-term goal of this project is to understand how differences in transport function in AAPs are related to differences in amino acid sequence. The main goal of this thesis work was to identify differences in AAP function. Electrophysiology was used to study the substrate specificity and substrate affinity of the rice and liverwort AAPs. Some of the rice and liverwort AAPs were found to have novel substrate specificities. Ancestral protein sequences were inferred and tested for function. Based on the results, the ability to transport basic amino acids is basal in AAPs. The inability to transport basic amino acids evolved independently at least twice in the AAP lineage.