Viewed from afar, the fossils take the form of tree trunks, spreading slightly near their base in a fashion that suggests a connection to unpreserved root-like structures.

[5] Concentric growth rings, sometimes containing embedded plant material,[6] suggest that the organism grew sporadically by the addition of external layers.

It is probable that the preserved trunk-like structures represent the fruiting body, or sporophore, of a fungus, which would have been fuelled by a mycelium, a net of dispersed filaments (hyphae).

[8] First collected in 1843,[9] it was not until 14 years later that John William Dawson, a Canadian scientist, studied Prototaxites fossils, which he described as partially rotten giant conifers, containing the remains of the fungi which had been decomposing them.

[12] Such was his fervour that he rebuked the name Prototaxites (loosely translated as "first yew"[13]) and insisted that the name Nematophycus ("stringy alga"[14]) be adopted,[6] a move strongly against scientific convention.

[15] Dawson fought adamantly to defend his original interpretation until studies of the microstructure made it clear that his position was untenable, whence he promptly attempted to rename the genus himself, calling it Nematophyton ("stringy plant"), and denying with great vehemence that he had ever considered it to be a tree.

[18] The lack of any characters diagnostic of any extant group made the presentation of a firm hypothesis difficult;[6] the fossil remained an enigmatic mystery and subject of debate.

It was not until 2001, after 20 years of research, that Francis Hueber, of the National Museum of Natural History in Washington, D.C., published a long-awaited paper which attempted to put Prototaxites in its place.

[26] It was the tallest living organism in its day by far; in comparison, the contemporary plant Cooksonia only reached 6 centimetres (2.4 in) in height and itself towered over the "moss forests" that grew beneath it, and invertebrates were the only other land-dwelling multi-cellular life.

[6] However, evidence of arthropod boreholes in Prototaxites has been found from the early and late Devonian, suggesting the organism survived the stress of boring for many millions of years.