[in Dutch with English summary: ] In 2020, lichenometric research was performed on Elegant sunburst lichen (Rusavskia elegans) to reconstruct the colonization of Maastricht (Netherlands). Maastricht, in the southernmost tip of the Netherlands, lies in a hilly countryside and borders the Meuse (‘Maas’ in Dutch), a rain river. To be able to estimate the age of the populations, the first step was calibrating the growth rate. That was not an unnecessary action, as the growth rate of 1.9 mm per year turned out to be four times higher than the current standard. The moderate climate and nitrogen deposition may play a role in this. The lichenometric research shows that colonization started around the year 1980 from the Meuse valley. Only from the year 2000 onward a clear increase in the number of branches has been noticeable. An accurate trend has also been determined for each location by measuring and dating each thallus. There appears to be a positive relationship between growth peaks and warm years. 47 locations have now been discovered within an area of 6 by 10 kilometres. Not only the oldest but also the largest populations – with hundreds of specimens – are situated in the Meuse valley. The urban centre is avoided, the conditions here may be too dry. From an ecological point of view, Elegant sunburst lichen follows the books. In our regions, this kind of lichen also prefers acidic to basic, warm, and sunny rocks of both natural and anthropogenic origin. The number of sites is enormous and varies from boulders, tombstones, brick walls, concrete bridges and posts to roof tiles and even iron. It is unusual that no clear relationship has been found with natural fertilization. It is possible that nitrogen deposition provides the necessary nutrients.