According to the Chinese Pharmacopoeia, the Chinese medicinal material (Asari Radix et Rhizoma) Xixin is derived from the species Asarum heterotropoides var. mandshuricum, A. sieboldii, and A. sieboldii var. seoulense. However, many species of the genus Asarum are labeled as "Xixin", "Tu-Xixin" or "Nan-Xixin" for sale in producing areas. To distinguish Chinese Asarum species and to ensure their safety and efficacy, we examined the microscopic characteristics of subg. Asarum plants in China (including subg. Asarum plants in the classification system of Flora Reipublicae Popularis Sinicae and the later published Asarum yunnanense) using a hand microtome and a microscopic digital imaging system based on our previous research. Microscopic features of the blades, petioles, and roots of A. yunnanense were investigated for the first time. Moreover, we compared nine species and one variety of the subg. Asarum (i.e. , A. yunnanense, A. caudigerellum, A. himalaicum, A. pulchellum, A. debile, A. caulescens, A. renicordatum, A. caudigerum, A. caudigerum var. cardiophyllum and A. geophilum) in China based on microscopic characteristics of the blades. Several parameters, such as morphological characteristics and distribution of hairs on both upper and lower leaf epidermises; morphological characteristics of hair cells; anticlinal walls of lower epidermal cells; size relationship between outer periclinal walls and cavity outlines of oil cells on lower leaf epidermis; presence or absence of the irregular cells containing red to brown substances among mesophyll cells; and the diameter of the largest vessels in midribs of the blades, were used for discrimination among species. To the best of our knowledge, we provided the first identification key for the 10 taxa based on blade microscopic characteristics that could be used to distinguish these taxa. Based on the key, 23 commercial samples collected from seven provinces of China were authenticated as whole dried herbs of A. himalaicum, A. caudigerellum, A. caudigerum, A. pulchellum and A. caulescens. These findings indicated that microscopic approach and related techniques were convenient and feasible and could be used for the authentication of crude drugs from Chinese subg. Asarum species.
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