Digitalis leaves are adulterated with the following:

1. The leaves of Verbascum thapsuse (Scrophulariaceae) are mixed with genuine drug and can be distinguished microscopically by the presence of large woolly branched trichomes.
2. The primrose leaves: The leaves of primrose are added to digitalis. They can be detected microscopically by the presence of uniseriate covering trichomes.
3. Comfrey leaves: It can be detected by the presence of multicellular trichomes forming hook at the top.