Gregarious in needle bed under Douglas fir. Known only from the type locality in Belgium, province de Namur.
Mycena flagellata is characterized by cheilocystidia terminated by a long and fine, tortuous, flagellum-like outgrowth. The cap is 3-4 mm wide, and it looks like species in sect. Polyadelphia. Molecular analysis on the ITS marker places M. flagellata in the vicinity of the blue-footed Mycenas (M. cyanorhiza and M. amicta).
Thanks to H. Cochard for the loan of his beautiful photo.