[in Dutch with English summary: ] Monitoring of lichens on veteran trees in the Wolfheze area (Gelderland province) led to the discovery of Microcalicium ahlneri, an ancient woodland indicator never recorded before in the Netherlands. Habitat, ecology and characteristics of the three European Microcalicium-species are briefly discussed. Microcalicium ahlneri forms mono-specific stands on large decorticated trunks of Quercus robur. The discovery of this minute coniocarp is surprising. According to international literature, the species is restricted to ancient woodland. In the Netherlands, however, its only known site is a clump of veteran oaks on the banks of an artificial stream, surrounded by a rather young mixed stand of Betula pendula, Pinus sylvestris and Sorbus aucuparia.