The Süderlügum inland dunes were already known in the past to be rich in lichens. The dune area, designated as a nature reserve, still has a large number of lichen species, some of which are rare and highly endangered in Schleswig-Holstein, in its remaining heathland and nutrient-poor dry grassland habitats. During several excursions in the years 2018-2022, the lichen flora of the area was recorded; 92 taxa could be detected. The results of the current mapping are compared with the records of the north German lichen expert C. F. E. Erichsen from the first decades of the 20th century, with those of P. Jacobsen and of S. Paus from the 1990s. It turns out that although some species previously found here have disappeared over time, some rarities of the native lichen flora that were previously unknown from here have now been documented for the first time. The rapidly progressing succession, eutrophication due to atmospheric nutrient inputs and the spread of the neophytic cactus moss (Campylopus introflexus) are identified as significant threats to the lichen flora in the area.