Objective: To elucidate the composition structure of "annual rings" and the formation process of anomalous structures in Sophora flavescens, and further discuss the medicinal parts of S. flavescens.
Method: Based on investigation on S. flavescens in its producing areas, the morphology of root systems was observed, and the developmental anatomy of roots was researched.
Result: Creeping underground rhizomes of S. flavescen existed in some parts of the north place, there were many differences in appearance characters and microscopic features between these roots and rhizomes. Parenchyma cells in secondary xylem regained meristematic ability, became into anomalous cambia, and then developed into anomalous structures. "Annual rings" in transverse section of S. flavescens were not actually growth rings, they were made up of anomalous parenchyma girdle in secondary xylem and normal secondary structure.
Conclusion: Roots are the medicinal parts of S. flavescens. This paper suggests that "annual rings" in the decoction pieces of S. flavescens should be called "annular structure".