Distinguishing the medicinal herb Oldenlandia diffusa from similar species of the same genus using fluorescence microscopy

The light microscope is routinely used for microscopic identification of Chinese Materia Medica (CMM). However, the fluorescence microscope has not been used for this purpose until now. The CMM, Baihuasheshecao, mostly used as a component of herb tea, is a well known folk-medicine in China. According to the Chinese Pharmacopoeia, its source is the species Oldenlandia diffusa (Willd.) Roxb. Two other species of the same genus, namely O. corymbosa (L.) Lam and O. tenelliflora Bl., had been found in use as Baihuasheshecao. To find a quick and easy method to distinguish O. diffusa from these similar species of the same genus, the fluorescence microscope was used to investigate the fluorescence emission characteristics of the three tissues, which were compared with light microscopy images of the same material. The results showed that some tissues of the three herbs emit autofluorescence. Specially, the wall of endoderm cells of O. diffusa and O. tenelliflora emit autofluorescence, while similar tissue of O. corymbosa does not. Hence, fluorescence microscopy can be helpful in the identification of CMM.