Dianlhus armeria was formerly considered to be a characteristic species of the Trifolio-Geranietea in the Netherlands. Its (syn-)ecology at two new localities described in this paper differs strongly from that. At the Veermansplaat in the Grevelingen estuary (province of Zeeland) it grows in Nanocyperion flavescentis and Caricion davallianae vegetation types (table 1) in increasing numbers (table 2). In Twente (eastern part of the Netherlands) it grows in an Arrhenatherion-Violion caninae vegetation. The synecological position of the species in western Europe is discussed. It is concluded that it occurs in gradient-rich grasslands belonging to quite different vegetation types. It is probably important that its localities in the Netherlands are managed by means of low-density grazing to keep the vegetation permanently open and to maintain the present low rate of primary production.