Objective The complex evolutionary history of the origin of medicinal blue herbs might result in the presence of adulterants, affecting the accuracy and safety of clinical medication. To provide a reference basis for the identification of medicinal blue herbs with leaves as the medicinal part, based on the leaf epidermis microstructure. Methods The species belonging to medicinal blue herbs and their close relatives (10 species from 4 genera) were systematically investigated. The leaf epidermis microstructure of these species was observed and analyzed by optical microscopy and scanning electron microscopy. A species retrieval table was established based on the microstructure characteristics. Results By combining the distribution of stomata, types of subsidiary cells, stomatal index, stomatal density, characteristics of the periclinal walls of epidermal cells, and epidermal appendages, the species Clerodendrum cyrtophyllum, Polygonum tinctorium, Isatis indigotica, I. violascens, I. costata, I. minima, Strobilanthes wallichii, S. dalzielii, S. pentstemonoides, and S. cusia can be accurately distinguished. Conclusion Microscopic characteristics of leaf epidermis can provide reference data for accurately differentiating the botanical origins of medicinal blue herbs.