Which chemicals would best indicate that an unknown substance is a plant?

To indicate that an unknown substance is a plant, the presence of chlorophyll, which is essential for photosynthesis, would be a key indicator. Additionally, detecting compounds such as cellulose, a primary component of plant cell walls, and various secondary metabolites like flavonoids or alkaloids can further confirm its plant origin. The presence of specific phytochemicals, such as terpenes, may also provide insights into the plant's species or family.