Prototaxites

Prototaxites /ˌproʊtoʊˈtæksɪtiːz/ is an extinct genus of large macroscopic eukaryote dating from the Late Silurian until the Late Devonian periods. Prototaxites formed large trunk-like structures up to 1 metre (3 ft) wide, reaching 8 metres (26 ft) in length, made up of tiny interwoven tubules around 50 micrometres (0.0020 in) in diameter, making it by far the largest land-dwelling organism of its time.

The taxonomy of Prototaxites has long been the subject of debate. It is widely considered a fungus, but the debate is ongoing. Its exact relationship with extant fungus lineages is uncertain. It was almost certainly a perennial organism that grew over multiple years. Several ecologies have been proposed, including that it was saprotrophic like many modern fungi, or that it was a lichenised autotroph.