Identification of Mucilage Cavity as a Significant Microscopic Characteristic Existing in Phloem Instead of Pith of Radix et Rhizoma Rhei

The morphologic and microscopic features of Radix et Rhizoma Rhei were studied. The study verified that the mucilage cavities did exist in phloem of rhizomes and roots or abnormal vascular bundles. Also, they were in similar distribution in three species of Radix et Rhizoma Rhei. The diagnostic characteristic for microscopic identification was found to be the similar distribution of abnormal vascular bundles in pith of rhizomes in all three species. And the appearance of the crude drug varied more depending on the plants＇ geographical origin and different preliminary treatment on the spot of collection than on the species differences. Our findings, having not been delineated clearly so far in the previous reports, are helpful for clarifying current descriptions in different literatures or standards and make a full understanding on microscopic and macroscopic identification of Radix et Rhizoma Rhei.