This fungus is always found with Common Alder Alnus glutinosa in particularly wet habitats, often in trooping groups

References: 
Breitenbach & Kranzlin (2000) Fungi of Switzerland, Volume 5, Agarics, 3rd Part
Overall (2017) Fungi: Mushroom & Toadstools of parks, gardens, heaths and woodlands
Hedger & George (2018) Lundy Fungi: a Photographic Guide