As a result of the expeditions carried out in 2018-2019 the research team has discovered a monocotyledonous plant (Ruppia maritima L., Ruppiaceae) from the bottom of Lake Sevan. This taxa is a new family, genus and species for the flora of the Republic of Armenia. The plant is quite widespread throughout the lake: it has been found from two points of Small Sevan and from four points of Big Sevan. This plant has been massively flowering and fruiting over the past two years, which was probably the reason for discovery and identify of this species.