Spongiophyton was a thallose fossil of the early to mid Devonian, which is notoriously difficult to classify. Spongiophyton displayed dichotomous branching, and a flattened/elliptical cross section with a thick (20–80 μm) upper cuticular surface. It is also perforated with pores resembling those of some liverworts. It probably grew on the banks of rivers. Spongiophyton has been mistakenly interpreted as tree resin and lycopod cuticle, and was later identified as the cuticle of a thalloid plant. It has most recently been interpreted on morphological and isotopic grounds as a lichen - which would make it the earliest known representative of this group.