Also known as Lyomyces sambuci. The common name is a bit misleading as this common species occurs on many other decaying wood species

References: 
Hugill & Lucas (2019) The Resupinates of Hampshire
Læssøe & Petersen (2019) Fungi of Temperate Europe, Volume 2
Bernicchia & Gorjon (2010) Fungi Europaei 12: Corticiaceae s.l.