Selected species of the genus Veronica (speedwells, family Plantaginaceae) - V. saturejoides ssp. saturejoides, V. austriaca ssp. jacquinii and V. officinalis, were collected in natural habitats in the Republic of Croatia. For these species, the phytochemical composition of free volatile compounds of essential oils and hydrosols was investigated by gas chromatography-mass spectrometry. The predominant compounds were hexahydrofarnesyl acetone and hexadecanoic acid. The same species were tested for antioxidant, antiproliferative and antiphytoviral activity. The species V. saturejoides ssp. saturejoides and V. officinalis showed stronger effects than V. austriaca ssp. jacquinii in most tests. Micromorphological research in all three species identified the glandular trichomes in which the synthesis of the investigated compounds primarily occurs. In the second part of the dissertation, the ITS regions and free volatile compounds of 18 species of speedwells were genetically analyzed. In addition to the above mentioned species, the material was collected and analyzed for: V. longifolia, V. acinifolia, V. anagallis-aquatica, V. beccabunga, V. catenata, V. serpyllifolia, V. anagalloides, V. montana, V. arvensis, V. chamaedrys, V. dalmatica, V. persica, V. polita, V. cymbalaria and V. hederifolia. By comparing the clusters obtained from genetic research with the phytochemical distribution of various volatile substances, a conclusion was reached about the possibility of using certain volatile components as chemophenetic markers for the genus Veronica.