Variation of the antimicrobial activity of Pseudognaphalium vira vira (Asteraceae): isolation and X-ray structure of ent-3β-hydroxy-16-kauren-19-oic acid - Rezende,M.C.; Urzúa,A.; Bortoluzzi,A.J.; Vásquez,L. (J Ethnopharmacol, 2000)