Prototaxites

The genus Prototaxites ( /ˌproʊtɵˈtæksɨtiːz/) describes terrestrial organisms known only from fossils dating from the Silurian and Devonian, approximately 420 to 370 million years ago. Prototaxites formed large trunk-like structures up to 1 metre (3 ft) wide, reaching 8 metres (26 ft) in height, made up of interwoven tubes just 50 micrometres (0.0020 in) in diameter. Whilst traditionally very difficult to assign to an extant group of organisms, current opinion is converging to a fungal placement for the genus. It might have had an algal symbiont, which would make it a lichen rather than a fungus in the strict sense.

An opposing view has been presented that Prototaxites was not a fungus but consisted of enrolled liverwort mats with associated cyanobacteria and fungal tubular elements.