A Middle Devonian Callixylon (Archaeopteridales) from Ronquières, Belgium

► We describe a Middle Devonian (mid to late Givetian) Callixylon from Belgium. ► The specimen is an 80 cm long, partially permineralized trunk. ► This Callixylon is one of the earliest representatives of the genus. ► It coexists at the locality with Crossia and an arborescent cladoxylopsid. ► The specimen shows that archaeopterids had evolved the tree habit by the Givetian.