This paper presents a series of researches conducted on two species belonging to the Equisetum genus, Equisetum arvense L. and Equisetum telmateia Ehrh., by establishing the amount of flavonoids, phenolic acids, antioxidant capacity and histo-anatomical characters. In the Romanian Pharmacopoeia 10th edition and in the European Pharmacopoeia (Ph. Eur. 7) only Equisetum arvense L. is mentioned as a source for Equiseti herba. The investigations showed differences regarding the histo-anatomical structures and the level of substances with antioxidant capacity which could be considered as a criterion for identifying possible substitutions.