The peat bog areas in southeastern Poland are a habitat for many interesting, often endangered, and rare or even new diatom species for Poland. Research conducted in the years 2022–2023 in three landscape parks (Pogórze Przemyskie Landscape Park, Południoworoztoczański Landscape Park, and Janowskie Forests Landscape Park) has allowed the identification of numerous rare and endangered species from the Pinnularia genus, including some that are new to Poland. The paper provides a detailed morphological and ecological characterization of six rare or endangered Pinnularia species, among which two were found to be new for Poland (Pinnularia lokana and P. esoxiformangusta).