New information is given on the habitats, distribution, population status and dynamics of 9 rare vascular plant species. The material was collected through floristic surveys carried out by the author in the Leningrad Region and St. Petersburg, mainly in 2018-2020. One of the species (Dactylorhiza baltica) is listed in the Red Data Book of the Russian Federation, three species (Alisma gramineum, A. juzepczukii, Persicaria mitis) are red-listed in Saint Petersburg, and two species (Carex arenaria, Viola persicifolia) are red-listed in the Leningrad Region. Most of the rare species records were made in the Zapadnyi Kotlin Nature Reserve. In addition, the article presents new information on rare alien species - Ambrosia artemisiifolia, Bidens frondosa, and Erigeron annuus. The invasive status of Bidens frondosa and the dynamics of its distribution in the region are discussed.