Iridoids from Euphrasia genargentea, a rare Sardinian endemism.

The phytochemical study of Euphrasia genargentea, a rare species only present in Sardinia, led to the identification of iridoid glucosides, i.e. aucubin, catalpol, mussaenosidic acid and melampyroside, which allowed chemotaxonomic considerations on the genus. On the basis of iridoid distribution in the genus, E. genargentea does not show any particular analogy with other Italian Euphrasia spp. This study is also important considering the severe risk of extinction of E. genargentea.