Despite the relevance of ecosystem services (ES) to society and modern ecological research, current methods of measurement and mapping remain inconsistent and often lack primary data in estimating and modeling ES. A key player in our understanding of ES and their measurements are plant functional traits—chemical and physical aspects of plants—which are often cited as one of the drivers of ecosystem processes and functions. In order to better quantify the ES–plant functional trait indicators, we outline existing evidence of this relationship and identify gaps between the best predicted ES and the most valued ES. This study offers an up-to-date review of plant functional traits’ direct or indirect relationships with ecosystem service provision and discusses the quantitative evidence these traits might hold as indicators. With this review, we seek to (1) offer a current summary of the quantitative evidence on ecosystem service–plant functional trait relationships, (2) identify which traits have been used to successfully indicate ecosystem services, and (3) identify research gaps, and ecosystem services or traits that receive little attention or have weak criteria as indicators. In a comprehensive literature review of the 19 services that were searched for, genetic materials, medicine, and cultural services had no relevant plant functional trait indicators, while the remaining 16 services had a range of traits associated with them. We found that functional traits showed varying relationships to ES, with some depending on the ecosystem type they were found in, while others appeared to remain consistent across ecosystems and conditions. This indicates that there could exist a subset of traits that are “universal” indicators across all ecosystem types, while others are ecosystem dependent. Our review suggests the need for more research on less clearly defined ES (such as cultural, educational, and refugium services) both by more careful definitions to make quantitative measures more applicable, and through increased quantitative and qualitative studies to better understand the nature of ES indicators for these services. This summary shows how plant functional traits can quantitatively and reliably predict and provide details on a subset of ES.