The Chinese materia medica "Nanshasheng" (Radix Adenophorae) specified in Chinese Pharmacopoeia (1995) is the dried root of Adenophora tetraphylla (Thunb.) Fisch. or A. stricta Miq. (Fam. Campanulaceae). Results of an investigation on the botanical origin of the drug showed that the roots of 30 species (subspecies, varieties) of the genus Adenophora are also used in certain districts in China. Thus, it is necessary to study and compare the histological characters of these roots. In this paper, the root structure of 18 species from Sect. Microdiscus are reported, viz. Adenophora brevidiscifera Hong, A. coelestis Diels, A. stricta Miq., A. stricta Miq. var. qinglongshanica P. F. Tu et G. J. Xu, A. stricta Miq. var. nanjingensis P. F. Tu et G. J. Xu, A. stricta Miq. subsp. henanica P. F. Tu et G. J. Xu, A. stricta Miq. subsp. sessilifolia Hong, A. longipedicellata Hong, A. gmelinii (Spreng.) Fisch., A. polyantha Nakai, A. micrantha Hong, A. stenophylla Hemsl., A. potaninii Korsh., A. bockiana Diels, A. wawreana Zahlbr., A. tricuspidata (Fisch. ex Roem. et Schult.) A. DC., A. pereskiifolia (Fisch. ex Roem. et Schult.) G. Don and A. divaricata Franch. et Sav.. According to the presence, arrangement and thickening of cell walls of sclerified cork cell (SCC) in cork tissue and the rate of secondary and anomalous structures, the histological structures of Adenophora roots are classified into types A, B and C. In type A, SCC are arranged in ring shape. Type A can be further classified into subtypes A1 and A2. Only the outer and anticlinal walls of SCC are thickened in subtype A1, and all cell walls of SCC are thickened in subtype A2. In type B, SCC are arranged scatteredly, not in ring shape. In type C, there is no SCC. Type C can be classified into subtypes C1, C2 and C3. In type C1, the secondary structure occupies more than 50% of the root diameter. In type C2, the anomalous structure is more than 50% of the root diameter, and the anomalous vascular bundles are in band form. The anomalous structure occupies more than 50% of the root diameter in subtype C3, and the anomalous vascular bundles are branched.