Highlight: Although large differences in metabolism exist between C 3 and CAM species, we find that many CAM genes have shared expression patterns regardless of photosynthetic pathway, suggesting ancestral propensity for CAM. Abstract: Crassulacean acid metabolism (CAM) is a carbon-concentrating mechanism that has evolved numerous times across flowering plants and is thought to be an adaptation to water limited environments. CAM has been investigated from physiological and biochemical perspectives, but little is known about how plants evolve from C 3 to CAM at the genetic or metabolic level. Here we take a comparative approach in analyzing time-course data of C 3 , CAM, and C 3 +CAM intermediate Yucca (Asparagaceae) species. RNA samples were collected over a 24-hour period from both well-watered and drought-stressed plants and were clustered based on time-dependent expression patterns. Metabolomic data reveals differences in carbohydrate metabolism and antioxidant response between the CAM and C 3 species, suggesting changes to metabolic pathways are important for CAM evolution and function. However, all three species share expression profiles of canonical CAM pathway genes, regardless of photosynthetic pathway. Despite differences in transcript and metabolite profiles between the C 3 and CAM species, shared time-structured expression of CAM genes in both CAM and C 3 Yucca species suggests ancestral expression patterns required for CAM may have predated its origin in Yucca .