Methods using liquid chromatography with UV detection (LC-UV), thin-layer chromatography (TLC), and digital photomicroscopy were developed to distinguish between the different species of Scutellaria lateriflora L. and its adulterants Teucrium canadense L. and T. chamaedrys L. Chemically, the 70% ethanol extract of S. lateriflora is characterized by the presence of flavonoids--predominantly baicalin, lateriflorin, dihydrobaicalin, and baicalein. The major compounds of the 70% ethanol extract of T. canadense are phenylpropanoids, with verbascoside as the most prominent, and a variable amount of teucrioside. Teucrioside is the major compound in T. chamaedrys, but it is not present in S. lateriflora. The presence of phenylpropane glycosides can therefore be used to distinguish between the S. lateriflora L. and the two Teucrium species by LC-UV and TLC. The abundant strap-shaped trichomes on the stem, as well as bristle-like trichomes on the leaf, are typically seen microscopically for T. canadense, whereas the waxy cuticle with numerous glandular scales is found in T. chamaedrys. These cell structures were used to determine the adulteration of S. lateriflora crude herb with either of the two Teucrium species.