WHO monographs on selected medicinal plants Organoleptic properties Odour, slight; taste, slightly sweet at first, followed by a sour or astringent taste and a slight bitterness (1, 2). Microscopic characteristics Literature description not available; to be established in accordance with national requirements. Powdered plant material Light greyish brown powder; masses of gelatinized starch granules fairly abundant, 5–25µm in diameter; clusters of calcium oxalate 11–35µm in diameter, packed in parenchyma cells in rows or singly; bordered, pitted, or reticulate vessels 20–65µm in diameter, walls thickened and slightly lignified (1, 2). Geographical distribution China, India, and Japan (6). General identity tests Macroscopic, microscopic, and microchemical examinations; thin-layer chromatographic analysis for the presence of the monoterpene glycoside paeoniflorin (1, 2). Purity tests Microbiology The test for Salmonella spp. in Radix Paeoniae products should be negative. The maximum acceptable limits of other microorganisms are as follows (9–11). For preparation of decoction: aerobic bacteria—not more than 107/g; fungi—not more than 105/g; Escherichia coli—not more than 102/g. Preparations for internal use: aerobic bacteria—not more than 105/g or ml; fungi—not more than 104/g or ml; enterobacteria and certain Gram-negative bacteria—not more than 103/g or ml; Escherichia coli—0/g or ml. Total ash Not more than 6.5% (1, 2). Acid-insoluble ash Not more than 0.5% (1). Pesticide residues To be established in accordance with national requirements. Normally, the maximum residue limit of aldrin and dieldrin for Radix Paeoniae is not more